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| features ? utilizes the avr ? risc architecture ? avr ? high-performance and low-power risc architecture ? 120 powerful instructions ? most single clock cycle execution ? 32 x 8 general purpose working registers ? fully static operation ? up to 20 mips throughput at 20 mhz ? data and non-volatile program and data memories ? 2k bytes of in-system self programmable flash endurance 10,000 write/erase cycles ? 128 bytes in-system programmable eeprom endurance: 100,000 write/erase cycles ? 128 bytes internal sram ? programming lock for flash pr ogram and eeprom data security ? peripheral features ? one 8-bit timer/counter with separate prescaler and compare mode ? one 16-bit timer/counter with separate prescaler, compare and capture modes ? four pwm channels ? on-chip analog comparator ? programmable watchdog timer with on-chip oscillator ? usi ? universal serial interface ? full duplex usart ? special microcontroller features ? debugwire on-chip debugging ? in-system programmable via spi port ? external and internal interrupt sources ? low-power idle, power-down, and standby modes ? enhanced power-on reset circuit ? programmable brown-out detection circuit ? internal calibrated oscillator ? i/o and packages ? 18 programmable i/o lines ? 20-pin pdip, 20-pin soic, 20-pad qfn/mlf ? operating voltages ? 1.8 ? 5.5v (attiny2313v) ? 2.7 ? 5.5v (attiny2313) ? speed grades ? attiny2313v: 0 ? 4 mhz @ 1.8 - 5.5v, 0 ? 10 mhz @ 2.7 ? 5.5v ? attiny2313: 0 ? 10 mhz @ 2.7 - 5.5v, 0 ? 20 mhz @ 4.5 ? 5.5v ? typical power consumption ? active mode 1 mhz, 1.8v: 230 a 32 khz, 1.8v: 20 a (including oscillator) ? power-down mode < 0.1 a at 1.8v 8-bit microcontroller with 2k bytes in-system programmable flash attiny2313/v preliminary rev. 2543l?avr?08/10
2 2543l?avr?08/10 attiny2313 pin configurations figure 1. pinout attiny2313 overview the attiny2313 is a low-power cmos 8-bit mi crocontroller based on the avr enhanced risc architecture. by executing powerful instructions in a single clo ck cycle, the attiny2313 achieves throughputs approaching 1 mips per mhz allowing the system designer to optimize power con- sumption versus processing speed. (reset/dw) pa2 (rxd) pd0 (txd) pd1 (xtal2) pa1 (xtal1) pa0 (ckout/xck/int0) pd2 (int1) pd3 (t0) pd4 (oc0b/t1) pd5 gnd 20 19 18 17 16 15 14 13 12 11 1 2 3 4 5 6 7 8 9 10 vcc pb7 (ucsk/scl/pcint7) pb6 (miso/do/pcint6) pb5 (mosi/di/sda/pcint5) pb4 (oc1b/pcint4) pb3 (oc1a/pcint3) pb2 (oc0a/pcint2) pb1 (ain1/pcint1) pb0 (ain0/pcint0) pd6 (icp) pdip/soic 1 2 3 4 5 mlf 15 14 13 12 11 20 19 18 17 16 6 7 8 9 10 (txd) pd1 xtal2) pa1 (xtal1) pa0 ( ckout/xck/int0) pd2 (int1) pd3 (t0) pd4 (oc0b/t1) pd5 gnd (icp) pd6 (ain0/pcint0) pb0 pb5 (mosi/di/sda/pcint 5) pb4 (oc1b/pcint4) pb3 (oc1a/pcint3) pb2 (oc0a/pcint2) pb1 (ain1/pcint1) pd0 (rxd) pa2 (reset/dw) vcc pb7 (ucsk/sck/pcint7) pb6 (miso/do/pcint6) note: bottom pad should be soldered to ground. 3 2543l?avr?08/10 attiny2313 block diagram figure 2. block diagram program counter program flash instruction register gnd vcc instruction decoder control lines stack pointer sram general purpose register alu status register programming logic spi 8-bit data bus xtal1 xtal2 reset internal oscillator oscillator watchdog timer timing and control mcu control register mcu status register timer/ counters interrupt unit eeprom usi usart analog comparator data register portb data dir. reg. portb data register porta data dir. reg. porta portb drivers pb0 - pb7 porta drivers pa0 - pa2 data register portd data dir. reg. portd portd drivers pd0 - pd6 on-chip debugger internal calibrated oscillator 4 2543l?avr?08/10 attiny2313 the avr core combines a rich instruction set wit h 32 general purpose working registers. all the 32 registers are directly connected to the arit hmetic logic unit (alu), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. the resulting architecture is more code efficient while achiev ing throughputs up to ten times faster than con- ventional cisc microcontrollers. the attiny2313 provides the following features: 2k bytes of in-system programmable flash, 128 bytes eeprom, 128 bytes sram, 18 general purpose i/o lines, 32 general purpose work- ing registers, a single-wire interface for on-c hip debugging, two flexib le timer/counters with compare modes, internal and external interrupts, a serial programmable usart, universal serial interface with start condition detect or, a programmable watchdog timer with internal oscillator, and three software selectable power saving modes. the idle mode stops the cpu while allowing the sram, timer/counters, and interrupt system to continue functioning. the power-down mode saves the regist er contents but free zes the oscillator, di sabling all other chip functions until the next interrupt or hardware re set. in standby mode, the crystal/resonator oscil- lator is running while the rest of the device is sleeping. this allows very fast start-up combined with low-power consumption. the device is manufactured using atmel?s high density non-volatile memory technology. the on-chip isp flash allows the program memory to be reprogrammed in-system through an spi serial interface, or by a conventional non-vol atile memory programmer. by combining an 8-bit risc cpu with in-system self-programmable fl ash on a monolithic chip, the atmel attiny2313 is a powerful microcontroller that provides a hi ghly flexible and cost effective solution to many embedded control applications. the attiny2313 avr is supported with a full suit e of program and system development tools including: c compilers, macro as semblers, program debugger/simu lators, in-circu it emulators, and evaluation kits. 5 2543l?avr?08/10 attiny2313 pin descriptions vcc digital supply voltage. gnd ground. port a (pa2..pa0) port a is a 3-bit bi-directional i/o port with inte rnal pull-up resistors (selected for each bit). the port a output buffers have symmetrical drive characteristics with both high sink and source capability. as inputs, port a pins that are externally pulled low will source current if the pull-up resistors are activated. the port a pins are tri-stated when a reset condition becomes active, even if the clock is not running. port a also serves the functions of various spec ial features of the attiny2313 as listed on page 53 . port b (pb7..pb0) port b is an 8-bit bi-directional i/o port with inte rnal pull-up resistors (selected for each bit). the port b output buffers have symmetrical drive characteristics with both high sink and source capability. as inputs, port b pins that are externally pulled low will source current if the pull-up resistors are activated. the port b pins are tri-stated when a reset condition becomes active, even if the clock is not running. port b also serves the functions of various spec ial features of the attiny2313 as listed on page 53 . port d (pd6..pd0) port d is a 7-bit bi-directional i/o port with inte rnal pull-up resistors (selected for each bit). the port d output buffers have symmetrical drive c haracteristics with bot h high sink and source capability. as inputs, port d pins that are exte rnally pulled low will source current if the pull-up resistors are activated. the port d pins are tri-stated when a reset condition becomes active, even if the clock is not running. port d also serves the functions of various special features of the attiny2313 as listed on page 56 . reset reset input. a low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running. the minimum pulse length is given in table 15 on page 34 . shorter pulses are not guaranteed to generate a reset. the reset input is an alternate func- tion for pa2 and dw. xtal1 input to the inverting oscillator amplifier and input to the internal clock operating circuit. xtal1 is an alternate function for pa0. xtal2 output from the inverting osc illator amplifier. xtal2 is an alternate func tion for pa1. 6 2543l?avr?08/10 attiny2313 general information resources a comprehensive set of development tools, appl ication notes and datashee ts are available for downloadon http: //www.atmel.com/avr. code examples this documentation contains simple code examples that briefly show how to use various parts of the device. these code examples assume that the part specific header file is included before compilation. be aware that not all c compiler vendors include bit definitions in the header files and interrupt handling in c is compiler dependent. please confirm with the c compiler documen- tation for more details. disclaimer typical values contained in this data sheet are based on simulations and characterization of other avr microcontrollers manufactured on th e same process technology. min and max values will be available after the device is characterized. 7 2543l?avr?08/10 attiny2313 avr cpu core introduction this section discusses the avr core architecture in general. the main function of the cpu core is to ensure correct program execution. the cpu must therefore be able to access memories, perform calculations, control peri pherals, and handle interrupts. architectural overview figure 3. block diagram of the avr architecture in order to maximize performance and parallelism, the avr uses a harvard architecture ? with separate memories and buses for program and data. instructions in the program memory are executed with a single level pipe lining. while one instruction is being executed, the next instruc- tion is pre-fetched from the program memory. this concept enables instructions to be executed in every clock cycle. the program memory is in-system reprogrammable flash memory. the fast-access register file contains 32 x 8-bit general purpose working registers with a single clock cycle access time. this allows single-cycle ar ithmetic logic unit (alu ) operation. in a typ- ical alu operation, two operands are output from the register file, the operation is executed, and the result is stored back in the register file ? in one clock cycle. flash program memory instruction register instruction decoder program counter control lines 32 x 8 general purpose registrers alu status and control i/o lines eeprom data bus 8-bit data sram direct addressing indirect addressing interrupt unit spi unit watchdog timer analog comparator i/o module 2 i/o module1 i/o module n 8 2543l?avr?08/10 attiny2313 six of the 32 registers can be used as three 16 -bit indirect address register pointers for data space addressing ? enabling efficient address calculations. one of the these address pointers can also be used as an address pointer for look up tables in flash program memory. these added function registers are the 16-bit x-, y-, and z-register, described later in this section. the alu supports arithmetic and logic operations between registers or between a constant and a register. single register operations can also be executed in the alu. after an arithmetic opera- tion, the status register is up dated to reflect information about the result of the operation. program flow is provided by conditional and uncon ditional jump and call instructions, able to directly address the whole addres s space. most avr instructions have a single 16-bit word for- mat. every program memory address co ntains a 16- or 32-bit instruction. during interrupts and subroutine calls, the return address program counter (pc) is stored on the stack. the stack is effectively allocated in th e general data sram, and consequently the stack size is only limited by the total sram size an d the usage of the sram. all user programs must initialize the sp in the reset routine (before subroutines or interrupts are executed). the stack pointer (sp) is read/write accessible in the i/o space. the data sram can easily be accessed through the five different addressing mo des supported in the avr architecture. the memory spaces in the avr architecture are all linear and regular memory maps. a flexible interrupt module has its control r egisters in the i/o spac e with an additional global interrupt enable bit in the status register. all interrupts have a s eparate interrupt vector in the interrupt vector table. the interrupts have priority in accordance with their interrupt vector posi- tion. the lower the interr upt vector address, the higher the priority. the i/o memory space contains 64 addresses for cpu peripheral functi ons as control regis- ters, and other i/o functions. the i/o memory can be accessed directly, or as the data space locations following those of the register file, 0x20 - 0x5f. alu ? arithmetic logic unit the high-performance avr alu operates in dire ct connection with all the 32 general purpose working registers. within a single clock cycle, arithmetic operations between general purpose registers or between a register and an immedi ate are executed. the alu operations are divided into three main categories ? arithmetic, logical, and bit-functions. some implementations of the architecture also provide a powerful multip lier supporting both signed/unsigned multiplication and fractional format. see the ?instruction set? section for a detailed description. status register the status register contains information about th e result of the most recently executed arithme- tic instruction. this information can be used for altering program flow in order to perform conditional operations. note that the status re gister is updated after all alu operations, as specified in the instructio n set reference. this will in many cases remove the need for using the dedicated compare instructions, resulting in faster and more compact code. the status register is not automatically st ored when entering an interrupt routine and restored when returning from an interrupt. this must be handled by software. 9 2543l?avr?08/10 attiny2313 the avr status register ? sreg ? is defined as: ? bit 7 ? i: global interrupt enable the global interrupt enable bit must be set for th e interrupts to be enabled. the individual inter- rupt enable control is then performed in separate control registers. if the global interrupt enable register is cleared, none of t he interrupts are enabled independent of the individual interrupt enable settings. the i-bit is cleared by hardware after an interrupt has occurred, and is set by the reti instruction to enable subsequent interr upts. the i-bit can also be set and cleared by the application with the sei and cli instructions, as described in the instructio n set reference. ? bit 6 ? t: bit copy storage the bit copy instructions bld (bit load) and bst (b it store) use the t-bi t as source or desti- nation for the operated bit. a bit from a register in the register file can be copied into t by the bst instruction, and a bit in t can be copied into a bit in a register in the register file by the bld instruction. ? bit 5 ? h: half carry flag the half carry flag h indicates a half carry in so me arithmetic operations. half carry is useful in bcd arithmetic. see the ?instruction set description? for detailed information. ? bit 4 ? s: sign bit, s = n v the s-bit is always an exclusive or between the negative flag n and the two?s complement overflow flag v. see the ?instruction set description? for detailed information. ? bit 3 ? v: two?s complement overflow flag the two?s complement overflow flag v suppor ts two?s complement arithmetics. see the ?instruction set description? for detailed information. ? bit 2 ? n: negative flag the negative flag n indicates a negative result in an arithmetic or logic operation. see the ?instruction set description? for detailed information. ? bit 1 ? z: zero flag the zero flag z indicates a zero result in an arithmetic or logic operation. see the ?instruction set description? for detailed information. ? bit 0 ? c: carry flag the carry flag c indicates a carry in an arithmetic or logic operation. see the ?instruction set description? for de tailed information. general purpose register file the register file is optimized for the avr enhanc ed risc instruction set. in order to achieve the required performance and flex ibility, the following in put/output schemes ar e supported by the register file: ? one 8-bit output operand and one 8-bit result input ? two 8-bit output operands and one 8-bit result input ? two 8-bit output operands and one 16-bit result input ? one 16-bit output operand and one 16-bit result input figure 4 shows the structure of the 32 genera l purpose working registers in the cpu. bit 76543210 i t h s v n z c sreg read/write r/w r/w r/ wr/wr/wr/wr/wr/w initial value 0 0 0 0 0 0 0 0 10 2543l?avr?08/10 attiny2313 figure 4. avr cpu general purpose working registers most of the instructions operating on the register file have direct access to all registers, and most of them are single cycle instructions. as shown in figure 4 , each register is also assigned a data memory address, mapping them directly into the first 32 loca tions of the user data space. although not being physically imple- mented as sram locations, this memory organizati on provides great flexibility in access of the registers, as the x-, y- and z-pointer registers can be set to index any register in the file. the x-register, y- register, and z-register the registers r26..r31 have some added functi ons to their general purpose usage. these reg- isters are 16-bit address pointers for indirect addressing of the data space. the three indirect address registers x, y, and z are defined as described in figure 5 . figure 5. the x-, y-, and z-registers in the different addressing modes these address registers have functions as fixed displacement, automatic increment, and automatic decrement (s ee the instruction set reference for details). 7 0 addr. r0 0x00 r1 0x01 r2 0x02 ? r13 0x0d general r14 0x0e purpose r15 0x0f working r16 0x10 registers r17 0x11 ? r26 0x1a x-register low byte r27 0x1b x-register high byte r28 0x1c y-register low byte r29 0x1d y-register high byte r30 0x1e z-register low byte r31 0x1f z-register high byte 15 xh xl 0 x-register 7 0 7 0 r27 (0x1b) r26 (0x1a) 15 yh yl 0 y-register 7 0 7 0 r29 (0x1d) r28 (0x1c) 15 zh zl 0 z-register 7 0 7 0 r31 (0x1f) r30 (0x1e) 11 2543l?avr?08/10 attiny2313 stack pointer the stack is mainly used for storing temporary data, for storing local variables and for storing return addresses after interrupts and subroutine calls. the stack pointer register always points to the top of the stack. note that the stack is implemented as growing from higher memory loca- tions to lower memory location s. this implies that a stack push command decreases the stack pointer. the stack pointer points to the data sram stack area where the subroutine and interrupt stacks are located. this stack space in the da ta sram must be defined by the program before any subroutine calls are executed or interrupt s are enabled. the stack pointer must be set to point above 0x60. the stack pointer is decrement ed by one when data is pushed onto the stack with the push instruction, and it is decremented by two when the return address is pushed onto the stack with subroutine call or interrupt. the st ack pointer is incremented by one when data is popped from the stack with the pop instruction, and it is incremented by two when data is popped from the stack with return from subr outine ret or return from interrupt reti. the avr stack pointer is implemented as two 8- bit registers in the i/o space. the number of bits actually used is implementation dependent. no te that the data space in some implementa- tions of the avr architecture is so small that only spl is needed. in this case, the sph register will not be present. instruction execution timing this section describes the general access timing concepts for instructi on execution. the avr cpu is driven by the cpu clock clk cpu , directly generated from the selected clock source for the chip. no internal clo ck division is used. figure 6 shows the parallel instruction fetches and instruction executions enabled by the har- vard architecture and the fast-acc ess register file concept. this is the basic pipelining concept to obtain up to 1 mips per mhz with the corr esponding unique results for functions per cost, functions per clocks, and functions per power-unit. figure 6. the parallel instruction fetches and instruction executions figure 7 shows the internal timing concept for the register file. in a single clock cycle an alu operation using two register operands is executed, and the result is stored back to the destina- tion register. bit 151413121110 9 8 ????????sph sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0 spl 76543210 read/writerrrrrrrr r/w r/w r/w r/w r/w r/w r/w r/w initial value ramend ramend ramend ramend ramend ramend ramend ramend ramend ramend ramend ramend ramend ramend ramend ramend clk 1st instruction fetch 1st instruction execute 2nd instruction fetch 2nd instruction execute 3rd instruction fetch 3rd instruction execute 4th instruction fetch t1 t2 t3 t4 cpu 12 2543l?avr?08/10 attiny2313 figure 7. single cycle alu operation reset and interrupt handling the avr provides several different interrupt sources. these interrupts and the separate reset vector each have a separate program vector in the program memory space. all interrupts are assigned individual enable bits which must be writ ten logic one together with the global interrupt enable bit in the status register in order to enable the interrupt. the lowest addresses in the program memory space are by default defined as the reset and interrupt vectors. the complete list of vectors is shown in ?interrupts? on page 44 . the list also determines the priority levels of the different interrupts. the lower the address the higher is the priority level. reset has the highest priority, and next is int0 ? the external interrupt request 0. refer to ?interrupts? on page 44 for more information. when an interrupt occurs, the global interrupt enable i-bit is cleared and all interrupts are dis- abled. the user software can write logic one to the i-bit to enable nested interrupts. all enabled interrupts can then interrupt the current interrupt routine. the i-bit is automatically set when a return from interrupt instru ction ? reti ? is executed. there are basically two types of interrupts. the fi rst type is triggered by an event that sets the interrupt flag. for these interrup ts, the program counter is vector ed to the actual interrupt vector in order to execute the interrupt handling rout ine, and hardware clears the corresponding inter- rupt flag. interrupt flags can also be cleared by wr iting a logic one to the flag bit position(s) to be cleared. if an interrupt condition occurs while the corresponding interrupt enable bit is cleared, the interrupt flag will be set and re membered until the inte rrupt is enabled, or the flag is cleared by software. similarly, if one or more interrupt condit ions occur while the global interrupt enable bit is cleared, the corresponding interrupt flag(s) w ill be set and remembered until the global interrupt enable bit is set, and will th en be executed by order of priority. the second type of interrupts will trigger as long as the interrupt condition is present. these interrupts do not necessarily have interrupt flags. if the interrupt condition disappears before the interrupt is enabled, the in terrupt will not be triggered. when the avr exits from an inte rrupt, it will always retu rn to the main pr ogram and execute one more instruction before any pending interrupt is served. note that the status register is not automatically stored when entering an interrupt routine, nor restored when returning from an interrupt routine. this must be handled by software. when using the cli instruction to disable interrupts, the interrup ts will be immediately disabled. no interrupt will be ex ecuted after the cli instru ction, even if it occurs simultaneously with the total execution time register operands fetch alu operation execute result write back t1 t2 t3 t4 clk cpu 13 2543l?avr?08/10 attiny2313 cli instruction. the following example shows how th is can be used to avoid interrupts during the timed eeprom write sequence.. when using the sei instruction to enable interr upts, the instruction following sei will be exe- cuted before any pending interrupts, as shown in this example. interrupt response time the interrupt execution response for all the enabled avr interrupts is four clock cycles mini- mum. after four clock cycles the program vector address for the actual interrupt handling routine is executed. during this four clock cycle perio d, the program counter is pushed onto the stack. the vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. if an interrupt occurs during execution of a multi- cycle instruction, this in struction is completed before the interrupt is served. if an interrupt occurs when the mcu is in sleep mode, the interrupt execution response time is increased by four clo ck cycles. this increase co mes in addition to the start-up time from the selected sleep mode. a return from an interrupt handling routine take s four clock cycles. during these four clock cycles, the program counter (two bytes) is po pped back from the stack, the stack pointer is incremented by two, and the i-bit in sreg is set. assembly code example in r16, sreg ; store sreg value cli ; disable interrupts during timed sequence sbi eecr, eempe ; start eeprom write sbi eecr, eepe out sreg, r16 ; restore sreg value (i-bit) c code example char csreg; csreg = sreg; /* store sreg value */ /* disable interrupts during timed sequence */ __disable_interrupt(); eecr |= (1< 15 2543l?avr?08/10 attiny2313 sram data memory figure 9 shows how the attiny2313 sram memory is organized. the lower 224 data memory locations address bot h the register file, the i/o memory, extended i/o memory, and the internal data sram. the firs t 32 locations address the register file, the next 64 location the standard i/o memory, and the next 128 locations address the internal data sram. the five different addressing modes for the data memory cover: direct, indirect with displace- ment, indirect, indirect with pre-decrement, and indirect with post-increment. in the register file, registers r26 to r31 feature the indirect addressing pointer registers. the direct addressing reaches the entire data space. the indirect with displacement mode reaches 63 address locations from the base address given by the y- or z-register. when using register indirect addressing modes with automatic pre-decrement and post-incre- ment, the address registers x, y, and z are decremented or incremented. the 32 general purpose working registers, 64 i/o registers, and the 128 bytes of internal data sram in the attiny2313 are all accessible th rough all these addressing modes. the register file is described in ?general purpose register file? on page 9 . figure 9. data memory map data memory access times this section describes the general access timi ng concepts for internal memory access. the internal data sram access is performed in two clk cpu cycles as described in figure 10 . 32 registers 64 i/o registers internal sram (128 x 8) 0x0000 - 0x001f 0x0020 - 0x005f 0x00df 0x0060 data memory 16 2543l?avr?08/10 attiny2313 figure 10. on-chip data sram access cycles eeprom data memory the attiny2313 contains 128 bytes of data eepro m memory. it is organized as a separate data space, in which single by tes can be read and wr itten. the eeprom has an endurance of at least 100,000 write/erase cycles. the access between the eeprom and the cpu is described in the following, specif ying the eeprom address registers, the eeprom data register, and the eeprom control register. for a detailed description of serial data downloading to the eeprom, see page 172 . eeprom read/write access the eeprom access registers are accessible in the i/o space. the write access time for the eeprom is given in table 1 . a self-timing func tion, however, lets the user software detect when the next byte can be written. if the user code contains instructions that write the eeprom, some precau tions must be taken. in heavily filtered power supplies, v cc is likely to rise or fall slowly on power-up/down. this causes the device for some period of time to run at a voltage lower than specified as minimum for the clock frequency used. see ?preventing eeprom corruption? on page 20. for details on how to avoid problems in these situations. in order to prevent unintentional eeprom writes, a specific write procedure must be followed. refer to the description of the eeprom control regist er for details on this. when the eeprom is read, the cpu is halted for fo ur clock cycles before the next in struction is executed. when the eeprom is written, the cpu is halte d for two clock cycles before the next instruction is executed. the eeprom address register ? bit 7 ? res: reserved bit this bit is reserved in the attiny 2313 and will always read as zero. clk wr rd data data address address valid t1 t2 t3 compute address read write cpu memory access instruction next instruction bit 76543210 ? eear6 eear5 eear4 eear3 eear2 eear1 eear0 eear read/write r r/w r/w r/w r/w r/w r/w r/w initial value 0 x x x x x x x 17 2543l?avr?08/10 attiny2313 ? bits 6..0 ? eear6..0: eeprom address the eeprom address register ? eear spec ify the eeprom address in the 128 bytes eeprom space. the eeprom da ta bytes are addressed linearly between 0 and 127. the ini- tial value of eear is undefi ned. a proper value must be wr itten before the eeprom may be accessed. the eeprom data register ? eedr ? bits 7..0 ? eedr7..0: eeprom data for the eeprom write operation, the eedr register contains the data to be written to the eeprom in the address given by the eear regi ster. for the eeprom read operation, the eedr contains the data read out from the eeprom at the add ress given by eear. the eeprom control register ? eecr ? bits 7..6 ? res: reserved bits these bits are reserved bits in the attiny2313 and will a lways read as zero. ? bits 5, 4 ? eepm1 and eepm0: eeprom programming mode bits the eeprom programming mode bits setting def ines which programming action that will be triggered when writing eepe. it is possible to program data in one atomic operation (erase the old value and program the new value) or to split the erase and write operations in two different operations. the programming times for the different modes are shown in table 1 . while eepe is set, any write to eepmn will be ignored. during reset, the eepmn bits will be reset to 0b00 unless the eeprom is busy programming. ? bit 3 ? eerie: eeprom ready interrupt enable writing eerie to one enables the eeprom ready interrupt if the i-bit in sreg is set. writing eerie to zero disables the interrupt. the eep rom ready interrupt gener ates a constant inter- rupt when non-volatile memory is ready for programming. bit 76543210 msb lsb eedr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 ? ? eepm1 eepm0 eerie eempe eepe eere eecr read/write r r r/w r/w r/w r/w r/w r/w initial value 0 0 x x 0 0 x 0 table 1. eeprom mode bits eepm1 eepm0 programming time operation 0 0 3.4 ms erase and write in one operation (atomic operation) 0 1 1.8 ms erase only 1 0 1.8 ms write only 1 1 ? reserved for future use 18 2543l?avr?08/10 attiny2313 ? bit 2 ? eempe: eeprom master program enable the eempe bit determines whether writing eepe to o ne will have effect or not. when eempe is set, setting eepe within four cl ock cycles will program the eeprom at the selected address. if eempe is zero, setting eepe will have no effect. when eempe has been written to one by software, hardware clears the bit to zero after four clock cycles. ? bit 1 ? eepe: eeprom program enable the eeprom program enable signal eepe is th e programming enable signal to the eeprom. when eepe is written, the ee prom will be programmed accord ing to the eepmn bits setting. the eempe bit must be written to one before a logical one is written to eepe, otherwise no eeprom write takes place. when the write access time has elapsed, the eepe bi t is cleared by hardware. wh en eepe has been set, the cpu is halted for two cycles be fore the next instruction is executed. ? bit 0 ? eere: eeprom read enable the eeprom read enable signal ? eere ? is t he read strobe to the eeprom. when the cor- rect address is set up in the eear register, the eere bit must be written to one to trigger the eeprom read. the eeprom read access takes one instruction, and the requ ested data is available immediately. when t he eeprom is read, the cpu is ha lted for four cycles before the next instruction is executed. th e user should poll the eepe bit be fore starting the read opera- tion. if a write operation is in progress, it is neither possible to read the eeprom, nor to change the eear register. atomic byte programming using atomic byte programming is the simplest mode. when writing a by te to the eeprom, the user must write the address into the eear regi ster and data into ee dr register. if the eepmn bits are zero, writing eepe (within four cycles af ter eempe is written) will trigger the erase/write operation. both the erase and write cycle are done in one operation and the total programming time is given in table 1. the eepe bit remains set until the erase and write operations are com- pleted. while the device is busy with programmin g, it is not possible to do any other eeprom operations. split byte programming it is possible to split the erase and write cycle in two different operations. this may be useful if the system requires short access time for some limited period of ti me (typically if the power sup- ply voltage falls). in order to take advantage of th is method, it is required that the locations to be written have been erased before the write oper ation. but since the erase and write operations are split, it is possible to do the erase operatio ns when the system allows doing time-consuming operations (typically after power-up). erase to erase a byte, the address must be written to eear. if the eepmn bits are 0b01, writing the eepe (within four cycles after eempe is written) will trigger the er ase operation on ly (program- ming time is given in table 1). the eepe bit remains set until the erase operation completes. while the device is busy prog ramming, it is not po ssible to do any othe r eeprom operations. write to write a location, the user must write the address into eear and the data into eedr. if the eepmn bits are 0b10, writing the eepe (within four cycles after eempe is written) will trigger the write operation only (programming time is given in t able 1). the eepe bit remains set until the write operation completes. if the location to be written has not been erased before write, the data that is stored must be cons idered as lost. while the device is busy with programming, it is not possible to do any other eeprom operations. the calibrated oscillator is used to time the eeprom accesses. make sure the oscillator fre- quency is within the requirements described in ?oscillator calibration register ? osccal? on page 26 . 19 2543l?avr?08/10 attiny2313 the following code examples show one assembly and one c function for writing to the eeprom. the examples assume that interrupts are controlled (e.g. by dis abling interrupts glob- ally) so that no interrupts will occu r during execution of these functions. assembly code example eeprom_write: ; wait for completion of previous write sbic eecr,eepe rjmp eeprom_write ; set up address (r17) in address register out eear, r17 ; write data (r16) to data register out eedr,r16 ; write logical one to eempe sbi eecr,eempe ; start eeprom write by setting eepe sbi eecr,eepe ret c code example void eeprom_write( unsigned int uiaddress, unsigned char ucdata) { /* wait for completion of previous write */ while(eecr & (1< 22 2543l?avr?08/10 attiny2313 system clock and clock options clock systems and their distribution figure 11 presents the principal clock systems in the avr and their distribution. all of the clocks need not be active at a given time. in order to reduce power consumption, the clocks to modules not being used can be halted by using different sleep modes, as described in ?power manage- ment and sleep modes? on page 30 . the clock systems are detailed below. figure 11. clock distribution cpu clock ? clk cpu the cpu clock is routed to parts of the syst em concerned with operat ion of the avr core. examples of such modules are the general pur pose register file, the status register and the data memory holding the stack po inter. halting the cpu clock inhi bits the core from performing general operations and calculations. i/o clock ? clk i/o the i/o clock is used by the majority of the i/o modules, like timer/counters, and usart. the i/o clock is also used by the external interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such interrupts to be detected even if the i/o clock is halted. also note that start condition detectio n in the usi module is carried out asynchronously when clk i/o is halted, enabling usi start condition detection in all sleep modes. flash clock ? clk flash the flash clock controls operation of the flash interface. the flash clock is usually active simul- taneously with the cpu clock. general i/o modules cpu core ram clk i/o avr clock control unit clk cpu flash and eeprom clk flash source clock watchdog timer watchdog oscillator reset logic clock multiplexer watchdog clock calibrated rc oscillator crystal oscillator external clock 23 2543l?avr?08/10 attiny2313 clock sources the device has the following clock source options, selectable by flash fuse bits as shown below. the clock from the selected source is inpu t to the avr clock generator, and routed to the appropriate modules. note: 1. for all fuses ?1? means unprogrammed while ?0? means programmed. the various choices for each clocking option is given in the following sections. when the cpu wakes up from power-down, the se lected clock source is used to time the start-up, ensuring sta- ble oscillator operation before instruction execution starts. when the cpu starts from reset, there is an additional delay allowing the power to reach a stable level before commencing nor- mal operation. the watchdog osc illator is used for timi ng this real-time part of the start-up time. the number of wdt oscillator cycles us ed for each time- out is shown in table 3 . the frequency of the watchdog oscillator is voltage dependent as shown in ?attiny2313 typical characteris- tics? on page 181 . default clock source the device is shipped with cksel = ?0100?, sut = ?10?, and ckdiv8 programmed. the default clock source setting is the internal rc oscillator with longes t start-up time and an initial system clock prescaling of 8, resulting in 1.0 mhz syst em clock. this default setting ensures that all users can make their desired clock source setting using an in-system or parallel programmer. crystal oscillator xtal1 and xtal2 are input and output, respectively, of an inverting amplifier which can be con- figured for use as an on-chi p oscillator, as shown in figure 12 on page 24 . either a quartz crystal or a ceramic resonator may be used. c1 and c2 should always be equal for both crystals and resonators. the optimal value of the capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the env ironment. some initial guidelines for choosing capacitors for use with crystals are given in table 4 on page 24 . for ceramic resonators, the capacitor values given by the manufacturer should be used. table 2. device clocking select (1) device clocking option cksel3..0 external clock 0000 calibrated internal rc oscillator 4mhz 0010 calibrated internal rc oscillator 8mhz 0100 watchdog oscillator 128khz 0110 external crystal/ceramic resonator 1000 - 1111 reserved 0001/0011/0101/0111 table 3. number of watchdog oscillator cycles typ time-out (v cc = 5.0v) typ time-out (v cc = 3.0v) number of cycles 4.1 ms 4.3 ms 512 65 ms 69 ms 8k (8,192) 24 2543l?avr?08/10 attiny2313 figure 12. crystal oscillator connections the oscillator can operate in three different mo des, each optimized for a specific frequency range. the oper ating mode is selected by the fuses cksel3..1 as shown in table 4 . notes: 1. the frequency ranges are prelimin ary values. actual values are tbd. 2. this option should not be used with crystals, only with ceramic resonators. the cksel0 fuse together with the sut1..0 fuses select the start-up times as shown in table 5 . table 4. crystal oscillator operating modes cksel3..1 frequency range (1) (mhz) recommended range for capacitors c1 and c2 for use with crystals (pf) 100 (2) 0.4 - 0.9 ? 101 0.9 - 3.0 12 - 22 110 3.0 - 8.0 12 - 22 111 8.0 - 12 - 22 xtal2 xtal1 gnd c2 c1 25 2543l?avr?08/10 attiny2313 notes: 1. these options should only be used when not operating close to the maximum frequency of the device, and only if frequency stability at start-up is not important for the application. these options are not suitable for crystals. 2. these options are intended for use with cerami c resonators and will ensure frequency stability at start-up. they can also be used with crystals when not operating close to the maximum fre- quency of the device, and if frequency stability at start-up is not important for the application. calibrated internal rc oscillator the calibrated internal rc oscillator provides a fixed 8.0 mhz clock. the frequency is nominal value at 3v and 25 c. if 8 mhz frequency exceeds the spec ification of the device (depends on v cc ), the ckdiv8 fuse must be programmed in orde r to divide the internal frequency by 8 dur- ing start-up. the device is shipped with t he ckdiv8 fuse programmed. this clock may be selected as the system cl ock by programming the cksel fuses as shown in table 6 . if selected, it will operate with no external com ponents. during reset, hardware loads the calibra- tion byte into the osccal register and thereby automatically calibrates the rc oscillator. at 3v and 25 c, this calibration gives a frequency with in 10% of the nominal frequency. using calibration methods as described in application no tes available at www.atmel.com/avr it is possi- ble to achieve 2% accuracy at any given v cc and temperature. when this oscillator is used as the chip clock, the watchdog oscillator will still be used for the watchdog timer and for the reset time-out. for more information on the pre-programmed calibration value, see the section ?calibration byte? on page 160 . note: 1. the device is shipped with this option selected. table 5. start-up times for the cryst al oscillator clock selection cksel0 sut1..0 start-up time from power-down and power-save additional delay from reset (v cc = 5.0v) recommended usage 0 00 258 ck (1) 14ck + 4.1 ms ceramic resonator, fast rising power 0 01 258 ck (1) 14ck + 65 ms ceramic resonator, slowly rising power 010 1k ck (2) 14ck ceramic resonator, bod enabled 011 1k ck (2) 14ck + 4.1 ms ceramic resonator, fast rising power 100 1k ck (2) 14ck + 65 ms ceramic resonator, slowly rising power 1 01 16k ck 14ck crystal oscillator, bod enabled 1 10 16k ck 14ck + 4.1 ms crystal oscillator, fast rising power 1 11 16k ck 14ck + 65 ms crystal oscillator, slowly rising power table 6. internal calibrated rc os cillator operating modes cksel3..0 nominal frequency 0010 - 0011 4.0 mhz 0100 - 0101 8.0 mhz (1) 26 2543l?avr?08/10 attiny2313 when this oscillator is select ed, start-up times are determined by the sut fuses as shown in table 7 . note: 1. the device is shipped with this option selected. oscillator calibration register ? osccal ? bits 6..0 ? cal6..0: oscillator calibration value writing the calibration byte to this address will trim the internal oscillator to remove process vari- ations from the oscillator frequency. this is done automatically during chip reset. when osccal is zero, the lowest available frequency is chosen. writing non-zero values to this regis- ter will increase the frequency of the internal oscillator. writing 0x7f to the register gives the highest available freque ncy. the calibrated oscillator is used to time eeprom and flash access. if eeprom or flash is wr itten, do not calibrate to more than 10% above the nominal fre- quency. otherwise, the eeprom or flash write may fail. note that the oscillator is intended for calibration to 8.0/4.0 mhz. tuning to other values is not guaranteed, as indicated in table 8 . avoid changing the calibration value in large steps when calibrating the calibrated internal rc oscillator to ensure stable operation of the mcu. a variation in fr equency of more than 2% from one cycle to the next can lead to unpredict able behavior. changes in osccal should not exceed 0x20 for ea ch calibration. table 7. start-up times for the internal calib rated rc oscillator clock selection sut1..0 start-up time from power- down and power-save additional delay from reset (v cc = 5.0v) recommended usage 00 6 ck 14ck bod enabled 01 6 ck 14ck + 4.1 ms fast rising power 10 (1) 6 ck 14ck + 65 ms slowly rising power 11 reserved bit 76543210 ? cal6 cal5 cal4 cal3 cal2 cal1 cal0 osccal read/write r r/w r/w r/w r/w r/w r/w r/w initial value device spec ific calibration value table 8. internal rc oscillator frequency range. osccal value min frequency in percentage of nominal frequency max frequency in percentage of nominal frequency 0x00 50% 100% 0x3f 75% 150% 0x7f 100% 200% 27 2543l?avr?08/10 attiny2313 external clock to drive the device from an external clock source, xtal1 should be driven as shown in figure 13 . to run the device on an external clock, th e cksel fuses must be programmed to ?0000?. figure 13. external clock drive configuration when this clock source is sele cted, start-up times are determi ned by the sut fuses as shown in table 10 . when applying an external clock, it is required to avoid sudden changes in the applied clock fre- quency to ensure stable operation of the mcu. a variation in frequency of more than 2% from one clock cycle to the next can lead to unpredictable behavior. it is required to en sure that the mcu is kept in reset during such changes in the clock frequency. note that the system clock prescaler can be used to implement run-time changes of the internal clock frequency while still en suring stable operation. table 9. crystal oscillator clock frequency cksel3..0 frequency range 0000 - 0001 0 - 16 mhz table 10. start-up times for the external clock selection sut1..0 start-up time from power- down and power-save additional delay from reset (v cc = 5.0v) recommended usage 00 6 ck 14ck bod enabled 01 6 ck 14ck + 4.1 ms fast rising power 10 6 ck 14ck + 65 ms slowly rising power 11 reserved nc external clock signal xtal2 xtal1 gnd 28 2543l?avr?08/10 attiny2313 128 khz internal oscillator the 128 khz internal oscillator is a low power os cillator providing a clock of 128 khz. the fre- quency is nominal at 3 v and 25 c. this clock may be selected as the system clock by programming the cksel fuses to 0110. when this clock source is sele cted, start-up times are determi ned by the sut fuses as shown in table 11 . system clock prescalar the attiny2313 has a system clock prescaler, and the system clock can be divided by setting the ?clkpr ? clock prescale register? on page 28 . this feature can be used to decrease the system clock frequency and the power consumption when the requirement for processing power is low. this can be used with all clock source options, and it will affect t he clock frequency of the cpu and all synchronous peripherals. clk i/o , clk cpu , and clk flash are divided by a factor as shown in table 12 on page 29 . when switching between prescaler settings, the system clock prescaler ensures that no glitches occurs in the clock system. it also ensu res that no intermediate frequency is higher than neither the clock frequency corresponding to th e previous setting, nor the clock frequency corre- sponding to the new setting. the ripple counter that implements the prescale r runs at the frequency of the undivided clock, which may be faster than the cpu' s clock frequency. hence, it is not possible to determine the state of the prescaler - even if it were readable, and the exact time it takes to switch from one clock division to the other cann ot be exactly predicted. from the time the clkps values are writ- ten, it takes between t1 + t2 and t1 + 2 * t2 before the new clock frequency is active. in this interval, two active clock edges are produced. here, t1 is the previous clock period, and t2 is the period corresponding to the new prescaler setting. to avoid unintentional changes of clock frequency, a special write procedure must be followed to change the clkps bits: 1. write the clock prescaler change enable (clkpce) bit to one and all other bits in clkpr to zero. 2. within four cycles, write the desired valu e to clkps while writing a zero to clkpce. interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted. clkpr ? clock prescale register ? bit 7 ? clkpce: clock prescaler change enable the clkpce bit must be written to logic one to enable ch ange of the clkps bits. the clkpce bit is only updated when the other bits in cl kpr are simultaneously wr itten to zero. clkpce is table 11. start-up times for the 128 khz internal oscillator sut1..0 start-up time from power- down and power-save additional delay from reset recommended usage 00 6 ck 14ck bod enabled 01 6 ck 14ck + 4 ms fast rising power 10 6 ck 14ck + 64 ms slowly rising power 11 reserved bit 76543210 clkpce ? ? ? clkps3 clkps2 clkps1 clkps0 clkpr read/write r/w r r r r/w r/w r/w r/w initial value 0 0 0 0 see bit description 29 2543l?avr?08/10 attiny2313 cleared by hardware four cycles af ter it is written or when clkps bits are written. rewriting the clkpce bit within this time-out period does neit her extend the time-out period, nor clear the clkpce bit. ? bits 3:0 ? clkps3:0: clock prescaler select bits 3:0 these bits define the division factor between th e selected clock source and the internal system clock. these bits can be written run-time to va ry the clock frequency to suit the application requirements. as the divider divides the master cl ock input to the mcu, the speed of all synchro- nous peripherals is reduced when a division fact or is used. the division factors are given in table 12 on page 29 . the ckdiv8 fuse determines the initial value of the clkps bits. if ckdiv8 is unprogrammed, the clkps bits will be reset to ?0000?. if ck div8 is programmed, clkps bits are reset to ?0011?, giving a division factor of 8 at start up. this feature should be used if the selected clock source has a higher frequency than the maximum frequency of the device at the present operat- ing conditions. note that any value can be wri tten to the clkps bits regardless of the ckdiv8 fuse setting. the application software must ensure that a sufficient division factor is chosen if the selected clock source has a higher frequen cy than the maximum frequency of the device at the present operating conditions. the device is shipped with the ckdiv8 fuse programmed. table 12. clock prescaler select clkps3 clkps2 clk ps1 clkps0 clock di vision factor 0000 1 0001 2 0010 4 0011 8 0100 16 0101 32 0110 64 0111 128 1000 256 1001 reserved 1010 reserved 1011 reserved 1100 reserved 1101 reserved 1110 reserved 1111 reserved 30 2543l?avr?08/10 attiny2313 power management and sleep modes sleep modes enable the application to shut down unused modules in the mcu, thereby saving power. the avr provides various sleep modes allowing the user to tailor the power consump- tion to the application?s requirements. to enter any of the three sleep modes, the se bit in mcucr must be written to logic one and a sleep instruction must be executed. the sm1 and sm0 bits in the mcucr register select which sleep mode (idle, power-down, or standby ) will be activated by the sleep instruction. see table 13 for a summary. if an enabled interrupt occurs while the mcu is in a sleep mode, the mcu wakes up. the mcu is then halted for four cycles in addition to the start-up time, exe- cutes the interrupt routine, an d resumes execution from the instruction following sleep. the contents of the register file and sram are unal tered when the device wakes up from sleep. if a reset occurs during sleep mode, the mcu wakes up and executes from the reset vector. figure 11 on page 22 presents the different clock systems in the attiny2313, and their distribu- tion. the figure is helpful in se lecting an appropriate sleep mode. mcu control register ? mcucr the sleep mode control register contai ns control bits for power management. ? bits 6, 4 ? sm1..0: sleep mode select bits 1 and 0 these bits select between the five available sleep modes as shown in table 13 . note: 1. standby mode is only recommended for use with external crystals or resonators. ? bit 5 ? se: sleep enable the se bit must be written to logic one to make the mcu enter the sleep mode when the sleep instruction is executed. to avoid the mcu entering the sleep mode unless it is the programmer?s purpose, it is recommended to wr ite the sleep enable (se) bit to one just before the execution of the sleep instruction and to clear it immediately af ter waking up. idle mode when the sm1..0 bits are wri tten to 00, the sleep instruction makes the mcu enter idle mode, stopping the cpu but al lowing the uart, analog comparat or, adc, usi, timer/counters, watchdog, and the interrupt system to continue operating. this sleep mode basically halts clk cpu and clk flash , while allowing the other clocks to run. idle mode enables the mcu to wake up from external triggered interrupts as well as internal ones like the timer overflow and uart transmit complete interrupts. if wake-up from the ana- log comparator interrupt is not required, the analog comparator can be powered down by setting the acd bit in the analog comparator control and status regist er ? acsr. this will reduce power consumption in idle mode. bit 76543210 pud sm1 se sm0 isc11 isc10 isc01 isc00 mcucr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 table 13. sleep mode select sm1 sm0 sleep mode 00idle 0 1 power-down 1 0 standby 1 1 power-down 31 2543l?avr?08/10 attiny2313 power-down mode when the sm1..0 bits are wri tten to 01 or 11, the sleep instruction makes the mcu enter power-down mode. in this mode, th e external oscilla tor is stopped, while th e external interrupts, the usi start condition detection, and the wa tchdog continue operating (if enabled). only an external reset, a watchdog reset, a brown-out rese t, usi start condition interrupt, an external level interrupt on int0, or a pin change interrupt can wake up the mcu. this sleep mode basi- cally halts all generated clocks, allowing operation of asynchronous modules only. note that if a level triggered interrupt is used for wake-up from power-down mode, the changed level must be held for some time to wake up the mcu. refer to ?external interrupts? on page 59 for details. when waking up from power-down mode, there is a delay from the wake-up condition occurs until the wake-up becomes effectiv e. this allows the clock to restart and become stable after having been stopped. the wake-up period is defined by the same cksel fuses that define the reset time-out period, as described in ?clock sources? on page 23 . standby mode when the sm1..0 bits are 10 and an external crystal/resonator clock option is selected, the sleep instruction makes the mcu enter standby mode. this mode is identical to power-down with the exception that the oscillator is kept running. fr om standby mode, the device wakes up in six clock cycles. notes: 1. only recommended with external crystal or resonator selected as clock source. 2. for int0, only level interrupt. minimizing power consumption there are several issues to consider when tryi ng to minimize the power consumption in an avr controlled system. in general, sleep modes shoul d be used as much as possible, and the sleep mode should be selected so that as few as possi ble of the device?s func tions are operating. all functions not needed should be disabled. in parti cular, the following modules may need special consideration when trying to achieve th e lowest possible power consumption. analog comparator when entering idle mode, the analog comparator should be disabled if not used. in other sleep modes, the analog comparator is automatically disabled. however, if the analog comparator is set up to use the internal voltage reference as input, the analog comp arator should be dis- abled in all sleep modes. ot herwise, the internal volt age reference will be enabled, independent of sleep mode. refer to ?analog comparator? on page 149 for details on how to configure the analog comparator. brown-out detector if the brown-out detector is not needed by the application, this module should be turned off. if the brown-out detector is enabled by the bo dlevel fuses, it will be enabled in all sleep modes, and hence, always consume pow er. in the deeper sl eep modes, this will contribute sig- table 14. active clock domains and wake-up sources in the different sleep modes. active clock domains oscillators wake-up sources sleep mode clk cpu clk flash clk io enabled int0, int1 and pin change usi start condition spm/eeprom ready other i/o wdt idle x x xxxxx power-down x (2) xx standby (1) xx (2) xx 32 2543l?avr?08/10 attiny2313 nificantly to the total current consumption. refer to ?brown-out detect ion? on page 35 for details on how to configure the brown-out detector. internal voltage reference the internal voltage re ference will be enabled when needed by the brown-out detection or the analog comparator. if these modules are disabled as described in the sections above, the inter- nal voltage reference will be disabled and it will not be consuming power. when turned on again, the user must allow the reference to start up before the output is used. if the reference is kept on in sleep mode, the output can be used immediately. refer to ?internal voltage reference? on page 38 for details on the start-up time. watchdog timer if the watchdog timer is not neede d in the application, the module should be turn ed off. if the watchdog timer is enabled, it will be enabled in all sleep modes, and hence, always consume power. in the deeper slee p modes, this will contribute signific antly to the total current consump- tion. refer to ?interrupts? on page 44 for details on how to configure the watchdog timer. port pins when entering a sleep mode, all port pins should be configured to use minimum power. the most important is then to ensure that no pins drive resistive loads. in sleep modes where the i/o clock (clk i/o ) is stopped, the input buff ers of the device will be dis abled. this ensures that no power is consumed by the input logic when not ne eded. in some cases, the input logic is needed for detecting wake-up conditions, and it will then be enabled. refer to the section ?digital input enable and sleep modes? on page 50 for details on which pins are enabled. if the input buffer is enabled and the input signal is left floati ng or have an analog signal level close to v cc /2, the input buffer will use excessive power. for analog input pins, the digital input buffer should be disabled at all times. an analog signal level close to v cc /2 on an input pin can cause significant current even in active mode. digital input buffers can be disabled by writing to the digital input di sable registers (didr). refer to ?digital input disable register ? didr? on page 150 . 33 2543l?avr?08/10 attiny2313 system control and reset resetting the avr during reset, all i/o registers are set to their initial values, and the pr ogram starts execution from the reset vector. the instruction placed at the reset vector must be an rjmp ? relative jump ? instruction to the reset handling routine. if the program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed at these locations. the circuit diagram in figure 14 shows the reset logic. table 15 defines the electrical parameters of th e reset circuitry. the i/o ports of the avr are immediately reset to their initial state when a reset source goes active. this does not require any clock source to be running. after all reset sources have gone inactive, a delay counter is invoked, stretching the internal reset. this allows the power to reach a stable level before normal operation starts. the time-out period of the delay counter is defined by the user through the sut and cksel fuses. the dif- ferent selections for the delay period are presented in ?clock sources? on page 23 . reset sources the attiny2313 has four sources of reset: ? power-on reset. the mcu is reset when the supply voltage is below the power-on reset threshold (v pot ). ? external reset. the mcu is reset wh en a low level is present on the reset pin for longer than the minimum pulse length. ? watchdog reset. the mcu is reset when the watchdog timer period expires, the watchdog is enabled, and watchdog interrupt is disabled. ? brown-out reset. the mcu is reset when the supply voltage v cc is below the brown-out reset threshold (v bot ) and the brown-out detector is enabled. figure 14. reset logic mcu status register (mcusr) brown-out reset circuit bodlevel [2..0] delay counters cksel[3:0] ck timeout wdrf borf extrf porf data b u s clock generator spike filter pull-up resistor watchdog oscillator sut [ 1:0 ] power-on reset circuit 34 2543l?avr?08/10 attiny2313 notes: 1. values are guidelines only. actual values are tbd. 2. the power-on reset will not work unless the supply voltage has been below v pot (falling) power-on reset a power-on reset (por) pulse is generated by an on-chip detection circuit. the detection level is defined in table 15 . the por is activated whenever v cc is below the detection level. the por circuit can be used to trigger the start-up reset, as well as to detect a failure in supply voltage. a power-on reset (por) circuit ensures that the device is reset from power-on. reaching the power-on reset threshold voltage invokes the delay counter, which determines how long the device is kept in reset after v cc rise. the reset signal is acti vated again, without any delay, when v cc decreases below the detection level. figure 15. mcu start-up, reset tied to v cc table 15. reset characteristics symbol parameter condition min (1) typ (1) max (1) units v pot power-on reset threshold voltage (rising) t a = -40 - to +85 c1.2 v power-on reset threshold voltage (falling) (2) t a = -40 to +85 c1.1 v v rst reset pin threshold voltage v cc = 1.8 - 5.5v 0.2 v cc 0.9 v cc v t rst minimum pulse width on reset pin v cc = 1.8 - 5.5v 2.5 s v reset time-out internal reset t tout v pot v rst cc 35 2543l?avr?08/10 attiny2313 figure 16. mcu start-up, reset extended externally external reset an external reset is generated by a low level on the reset pin. reset pulses longer than the minimum pulse width (see table 15 ) will generate a reset, even if the clock is not running. shorter pulses are not guaranteed to generate a reset. when the applied signal reaches the reset threshold voltage ? v rst ? on its positive edge, the delay counter starts the mcu after the time-out period ? t tout ? has expired. figure 17. external reset during operation brown-out detection attiny2313 has an on-chip brown-out detect ion (bod) circuit for monitoring the v cc level dur- ing operation by comparing it to a fixed trig ger level. the trigger level for the bod can be selected by the bodlevel fuses. the trigger level has a hysteresis to ensure spike free brown-out detection. the hysteresis on the detection level should be interpreted as v bot+ = v bot + v hyst /2 and v bot- = v bot - v hyst /2. reset time-out internal reset t tout v pot v rst v cc cc table 16. bodlevel fuse coding (1) bodlevel 2..0 fuses min v bot typ v bot max v bot units 111 bod disabled 110 1.8 v 101 2.7 100 4.3 36 2543l?avr?08/10 attiny2313 note: 1. v bot may be below nominal minimum operating voltage for some devices. for devices where this is the case, the de vice is tested down to v cc = v bot during the production test. this guar- antees that a brown-out reset will occur before v cc drops to a voltage where correct operation of the microcontroller is no longer guaranteed. the test is performed using bodlevel = 110 for attiny2313v and bodlevel = 101 for attiny2313l. when the bod is enabled, and v cc decreases to a value below the trigger level (v bot- in figure 18 ), the brown-out reset is i mmediately activated. when v cc increases above the trigger level (v bot+ in figure 18 ), the delay counter starts the mcu after the time-out period t tout has expired. the bod circuit will only detect a drop in v cc if the voltage stays below the trigger level for lon- ger than t bod given in table 15 . figure 18. brown-out reset during operation 011 reserved 010 001 000 table 17. brown-out characteristics symbol parameter min typ max units v hyst brown-out detector hysteresis 50 mv t bod min pulse width on brown-out reset 2 ns table 16. bodlevel fuse coding (1) bodlevel 2..0 fuses min v bot typ v bot max v bot units v cc reset time-out internal reset v bot- v bot+ t tout 37 2543l?avr?08/10 attiny2313 watchdog reset when the watchdog times out, it will generate a short reset pulse of one ck cycle duration. on the falling edge of this pulse, the delay ti mer starts counting the time-out period t tout . refer to page 44 for details on operation of the watchdog timer. figure 19. watchdog reset during operation mcu status register ? mcusr the mcu status register provides information on which reset source caused an mcu reset. ? bit 3 ? wdrf: watchdog reset flag this bit is set if a watchdog re set occurs. the bit is reset by a power-on reset, or by writing a logic zero to the flag. ? bit 2 ? borf: brown-out reset flag this bit is set if a brown-out reset occurs. the bi t is reset by a power-on reset, or by writing a logic zero to the flag. ? bit 1 ? extrf: external reset flag this bit is set if an external reset occurs. the bit is reset by a power-on reset, or by writing a logic zero to the flag. ? bit 0 ? porf: power-on reset flag this bit is set if a power-on reset occurs. the bit is reset only by writing a logic zero to the flag. to make use of the reset flags to identify a rese t condition, the user should read and then reset the mcusr as early as possible in the program. if the register is cleared before another reset occurs, the source of the reset can be found by examining the reset flags. ck cc bit 76543210 ? ? ? ? wdrf borf extrf porf mcusr read/write r r r r r/w r/w r/w r/w initial value 0 0 0 see bit description 38 2543l?avr?08/10 attiny2313 internal voltage reference attiny2313 features an internal bandgap reference. this reference is used for brown-out detec- tion, and it can be used as an input to the analog comparator. voltage reference enable signals and start-up time the voltage reference has a start-up time that may influence the way it should be used. the start-up time is given in table 18 . to save power, the reference is not always turned on. the ref- erence is on during the following situations: 1. when the bod is enabled (by pr ogramming the bodl evel [2..0] fuse). 2. when the bandgap reference is connected to the analog comparator (by setting the acbg bit in acsr). thus, when the bod is not enabled, after setting the acbg bit, the user must always allow the reference to start up before the output from t he analog comparator is used. to reduce power consumption in power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering power-down mode. note: 1. values are guidelines only. actual values are tbd. table 18. internal voltage reference characteristics (1) symbol parameter condi tion min typ max units v bg bandgap reference voltage v cc = 2.7v, t a = 25c 1.0 1.1 1.2 v t bg bandgap reference start-up time v cc = 2.7v, t a = 25c 40 70 s i bg bandgap reference current consumption v cc = 2.7v, t a = 25c 15 a 39 2543l?avr?08/10 attiny2313 watchdog timer attiny2313 has an enhanced watchdog ti mer (wdt). the main features are: ? clocked from separate on-chip oscillator ? 3 operating modes ? interrupt ? system reset ? interrupt and system reset ? selectable time-out period from 16ms to 8s ? possible hardware fuse watchdog al ways on (wdton) for fail-safe mode figure 20. watchdog timer the watchdog timer (wdt) is a timer counting cycles of a separa te on-chip 128 khz oscillator. the wdt gives an interrupt or a system reset when the counter reaches a given time-out value. in normal operation mode, it is required that the system uses the wdr - watchdog timer reset - instruction to restart the count er before the time-out value is reached. if the system doesn't restart the counter, an interrupt or system reset will be issued. in interrupt mode, the wdt gives an interrupt when the timer expires. this interrupt can be used to wake the device from sleep-modes, and also as a general system timer. one example is to limit the maximum time allowed for certain opera tions, giving an interrupt when the operation has run longer than expected. in system reset mode, the wdt gives a reset when the timer expires. this is typically used to prevent sys tem hang-up in case of runaway code. the third mode, interrupt and system reset mode, combines the other two modes by first giving an inter- rupt and then switch to system reset mode. th is mode will for instance allow a safe shutdown by saving critical parameters before a system reset. the watchdog always on (wdton ) fuse, if programmed, will forc e the watchdog timer to sys- tem reset mode. with the fuse programmed the system reset mode bit (wde) and interrupt mode bit (wdie) are locked to 1 and 0 respectively. to further ensure program security, alterations to the watchdog set-up must follow timed sequences. the sequence for clearing wde and ch anging time-out configur ation is as follows: 1. in the same operation, write a logic one to the watchdog change enable bit (wdce) and wde. a logic one must be written to wde re gardless of the previous value of the wde bit. 2. within the next four clock cycles, write the wde and watchdog prescaler bits (wdp) as desired, but with the wdce bit cleared. this must be done in one operation. 128khz oscillator osc/2k osc/4k osc/8k osc/16k osc/32k osc/64k osc/128k osc/256k osc/512k osc/1024k wdp0 wdp1 wdp2 wdp3 watchdog reset wde wdif wdie mcu reset interrupt 40 2543l?avr?08/10 attiny2313 the following code example shows one assembly and one c function for turning off the watch- dog timer. the example assumes that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during th e execution of these functions. note: 1. the example code assumes that the part specific header file is included. note: if the watchdog is accident ally enabled, for example by a runaway pointer or brown-out condition, the device will be reset and the watchdog timer will stay enabled. if the code is not set up to handle the watchdog, this might lead to an eternal loop of time-out resets. to avoid this situation, the application software should a lways clear the watchdog system reset flag (wdrf) and the wde control bit in the initialisatio n routine, even if the watchdog is not in use. assembly code example (1) wdt_off: ; turn off global interrupt cli ; reset watchdog timer wdr ; clear wdrf in mcusr in r16, mcusr andi r16, (0xff & (0< 43 2543l?avr?08/10 attiny2313 table 20. watchdog timer prescale select wdp3 wdp2 wdp1 wdp0 number of wdt oscillator cycles typical time-out at v cc = 5.0v 0 0 0 0 2k (2048) cycles 16 ms 0 0 0 1 4k (4096) cycles 32 ms 0 0 1 0 8k (8192) cycles 64 ms 0 0 1 1 16k (16384) cycles 0.125 s 0 1 0 0 32k (32768) cycles 0.25 s 0 1 0 1 64k (65536) cycles 0.5 s 0 1 1 0 128k (131072) cycles 1.0 s 0 1 1 1 256k (262144) cycles 2.0 s 1 0 0 0 512k (524288) cycles 4.0 s 1 0 0 1 1024k (1048576) cycles 8.0 s 1010 reserved 1011 1100 1101 1110 1111 44 2543l?avr?08/10 attiny2313 interrupts this section describes the specifics of the inte rrupt handling as performed in attiny2313. for a general explanation of the avr in terrupt handling, refer to ?reset and interrupt handling? on page 12 . interrupt vectors in attiny2313 table 21. reset and interrupt vectors vector no. program address source interrupt definition 1 0x0000 reset external pin, power-on reset, brown-out reset, and watchdog reset 2 0x0001 int0 external interrupt request 0 3 0x0002 int1 external interrupt request 1 4 0x0003 timer1 capt timer/counter1 capture event 5 0x0004 timer1 compa timer/counter1 compare match a 6 0x0005 timer1 ovf timer/counter1 overflow 7 0x0006 timer0 ovf timer/counter0 overflow 8 0x0007 usart0, rx usart0, rx complete 9 0x0008 usart0, udre usart0 data register empty 10 0x0009 usart0, tx usart0, tx complete 11 0x000a analog comp analog comparator 12 0x000b pcint pin change interrupt 13 0x000c timer1 compb timer /counter1 compare match b 14 0x000d timer0 compa timer/counter0 compare match a 15 0x000e timer0 compb timer/counter0 compare match b 16 0x000f usi start usi start condition 17 0x0010 usi overflow usi overflow 18 0x0011 ee ready eeprom ready 19 0x0012 wdt overflow watchdog timer overflow 45 2543l?avr?08/10 attiny2313 the most typical and general program setup fo r the reset and interrupt vector addresses in attiny2313 is: address labels code comments 0x0000 rjmp reset ; reset handler 0x0001 rjmp int0 ; external interrupt0 handler 0x0002 rjmp int1 ; external interrupt1 handler 0x0003 rjmp tim1_capt ; timer1 capture handler 0x0004 rjmp tim1_compa ; timer1 comparea handler 0x0005 rjmp tim1_ovf ; timer1 overflow handler 0x0006 rjmp tim0_ovf ; timer0 overflow handler 0x0007 rjmp usart0_rxc ; usart0 rx complete handler 0x0008 rjmp usart0_dre ; usart0,udr empty handler 0x0009 rjmp usart0_txc ; usart0 tx complete handler 0x000a rjmp ana_comp ; analog comparator handler 0x000b rjmp pcint ; pin change interrupt 0x000c rjmp timer1_compb ; timer1 compare b handler 0x000d rjmp timer0_compa ; timer0 compare a handler 0x000e rjmp timer0_compb ; timer0 compare b handler 0x000f rjmp usi_start ; usi start handler 0x0010 rjmp usi_overflow ; usi overflow handler 0x0011 rjmp ee_ready ; eeprom ready handler 0x0012 rjmp wdt_overflow ; watchdog overflow handler ; 0x0013 reset: ldi r16, low(ramend); main program start 0x0014 out spl,r16 set stack pointer to top of ram 0x0015 sei ; enable interrupts 0x0016 46 2543l?avr?08/10 attiny2313 i/o-ports introduction all avr ports have true read-modi fy-write functionality when used as general digital i/o ports. this means that the dire ction of one port pin can be chan ged without unintentionally changing the direction of any other pin with the sbi and cbi instructions. the same applies when chang- ing drive value (if configured as output) or enab ling/disabling of pull-up resistors (if configured as input). each output buffer has symmetrical drive characteristics with both high sink and source capability. the pin driver is stro ng enough to drive led displays directly. all port pins have indi- vidually selectable pull-up resistors with a suppl y-voltage invariant resistance. all i/o pins have protection diodes to both v cc and ground as indicated in figure 21 . refer to ?electrical charac- teristics? on page 177 for a complete list of parameters. figure 21. i/o pin equivalent schematic all registers and bit references in this section are written in general form. a lower case ?x? repre- sents the numbering letter for the port, and a lower case ?n? represents the bit number. however, when using the register or bit defines in a progr am, the precise form must be used. for example, portb3 for bit no. 3 in port b, here document ed generally as portxn. the physical i/o regis- ters and bit locations are listed in ?register description for i/o-ports? on page 58 . three i/o memory address locations are allocated for each port, one each for the data register ? portx, data direction register ? ddrx, and th e port input pins ? pi nx. the port input pins i/o location is read only, while th e data register and the data direction register are read/write. however, writing a logic one to a bit in the pinx register, will result in a toggle in the correspond- ing bit in the data register. in addition, the pull-up disable ? pud bit in mcuc r disables the pull-up function for all pins in all ports when set. using the i/o port as general digital i/o is described in ?ports as general digital i/o? on page 47 . most port pins are multiplexed with alternate functions for the peripheral features on the device. how each alternate function interferes with the port pin is described in ?alternate port functions? on page 51 . refer to the individual module sectio ns for a full description of the alter- nate functions. note that enabling the alternate function of some of the port pins does not affect the use of the other pins in the port as general digital i/o. c pin logic r pu see figure "general digital i/o" for details pxn 47 2543l?avr?08/10 attiny2313 ports as general digital i/o the ports are bi-directional i/o ports with optional internal pull-ups. figure 22 shows a functional description of one i/o-port pin, here generically called pxn. figure 22. general digital i/o (1) note: 1. wrx, wpx, wdx, rrx, rpx, and rdx are co mmon to all pins within the same port. clk i/o , sleep, and pud are common to all ports. configuring the pin each port pin consists of three register bits: ddxn, portxn, and pinxn. as shown in ?register description for i/o-ports? on page 58 , the ddxn bits are accessed at the ddrx i/o address, the portxn bits at the portx i/o address, and the pinxn bits at the pinx i/o address. the ddxn bit in the ddrx register selects the direct ion of this pin. if ddxn is written logic one, pxn is configured as an output pin. if ddxn is written logic ze ro, pxn is configured as an input pin. if portxn is written logic one w hen the pin is configured as an i nput pin, the pull-up resistor is activated. to switch the pull-up re sistor off, portxn has to be wr itten logic zero or the pin has to be configured as an output pin. the port pins are tri-stated when reset condition becomes active, even if no clocks are running. if portxn is written logic one when the pin is configured as an ou tput pin, the port pin is driven high (one). if portxn is writte n logic zero when the pin is config ured as an output pin, the port pin is driven low (zero). toggling the pin writing a logic one to pinxn toggles the value of portxn, independent on the value of ddrxn. note that the sbi instruction can be us ed to toggle one single bit in a port. clk rpx rrx rdx wdx pud synchronizer wdx: write ddrx wrx: write portx rrx: read portx register rpx: read portx pin pud: pullup disable clk i/o : i/o clock rdx: read ddrx d l q q reset reset q q d q q d clr portxn q q d clr ddxn pinxn data b u s sleep sleep: sleep control pxn i/o wpx 0 1 wrx wpx: write pinx register 48 2543l?avr?08/10 attiny2313 switching between input and output when switching between tri-state ({ddxn, port xn} = 0b00) and output high ({ddxn, portxn} = 0b11), an intermediate state with either pull-up enabled {ddxn, portxn} = 0b01) or output low ({ddxn, portxn} = 0b10) must occur. norma lly, the pull-up enabled state is fully accept- able, as a high-impedant enviro nment will not notice the differenc e between a strong high driver and a pull-up. if this is not the case, the pud bit in the mcucr register can be set to disable all pull-ups in all ports. switching between input with pull-up and output low generates the same problem. the user must use either the tri-state ({ddxn, portxn} = 0b00) or the output high state ({ddxn, portxn} = 0b11) as an intermediate step. table 22 summarizes the control signals for the pin value. reading the pin value independent of the setting of data direction bit ddxn, the port pin can be read through the pinxn register bit. as shown in figure 22 , the pinxn register bit and the preceding latch consti- tute a synchronizer. this is needed to avoid me tastability if the physical pin changes value near the edge of the internal clock, but it also introduces a delay. figure 23 shows a timing diagram of the synchronization when reading an externally applied pin val ue. the maximum and minimum propagation delays are denoted t pd,max and t pd,min respectively. figure 23. synchronization when reading an externally applied pin value table 22. port pin configurations ddxn portxn pud (in mcucr) i/o pull-up comment 0 0 x input no tri-state (hi-z) 0 1 0 input yes pxn will source current if ext. pulled low. 0 1 1 input no tri-state (hi-z) 1 0 x output no output low (sink) 1 1 x output no output high (source) xxx in r17, pinx 0x00 0xff instructions sync latch pinxn r17 xxx system clk t pd, max t pd, min 49 2543l?avr?08/10 attiny2313 consider the clock period starting shortly after the first falling edge of the system cl ock. the latch is closed when the clock is low, and goes transpa rent when the clock is high, as indicated by the shaded region of the ?sync latch? signal. the signal value is latched when the system clock goes low. it is clocked into the pinxn register at the succeeding positive clock edge. as indi- cated by the two arrows tpd,max and tpd,min, a single signal tr ansition on the pin will be delayed between ? and 1? system clock period depending upon the time of assertion. when reading back a software assigned pin value, a nop instruction must be inserted as indi- cated in figure 24 . the out instruction sets the ?sync latc h? signal at the positive edge of the clock. in this case, the delay tpd through the synchronizer is 1 system clock period. figure 24. synchronization when reading a software assigned pin value out portx, r16 nop in r17, pinx 0xff 0x00 0xff system clk r16 instructions sync latch pinxn r17 t pd 50 2543l?avr?08/10 attiny2313 the following code example shows how to set port b pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 7 as input with pull-ups as signed to port pins 6 and 7. the resulting pin values are read back again, but as previously di scussed, a nop instruction is included to be able to read back the value recently assigned to some of the pins. note: 1. for the assembly program, two temporary re gisters are used to minimize the time from pull- ups are set on pins 0, 1, 6, and 7, until the dire ction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as strong high drivers. digital input enable and sleep modes as shown in figure 22 , the digital input signal can be clam ped to ground at the input of the schmitt trigger. the signal deno ted sleep in the figure, is set by the mcu sleep controller in power-down mode, and standby mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to v cc /2. sleep is overridden for port pins enabled as ex ternal interrupt pins. if the external interrupt request is not e nabled, sleep is active also for these pi ns. sleep is also over ridden by various other alternate functions as described in ?alternate port functions? on page 51 . if a logic high level (?one?) is present on an asyn chronous external interrupt pin configured as ?interrupt on rising edge, falling edge, or any logic change on pin? while the external interrupt is not enabled, the corresponding external interrupt flag will be set when resuming from the above mentioned sleep mode, as the clamping in these sleep mode produces the requested logic change. assembly code example (1) ... ; define pull-ups and set outputs high ; define directions for port pins ldi r16,(1< 52 2543l?avr?08/10 attiny2313 the following subsections shortly describe the alte rnate functions for each port, and relate the overriding signals to the alternate function. refer to the alternate function description for further details. table 23. generic description of overriding signals for alternate functions signal name full name description puoe pull-up override enable if this signal is set, the pull-up enable is controlled by the puov signal. if this signal is cleared, the pull-up is enabled when {ddxn, portxn, pud} = 0b010. puov pull-up override value if puoe is set, the pull-up is enabled/disabled when puov is set/cleared, regardless of the setting of the ddxn, portxn, and pud register bits. ddoe data direction override enable if this signal is set, the outp ut driver enable is controlled by the ddov signal. if this si gnal is cleared, the output driver is enabled by the ddxn register bit. ddov data direction override value if ddoe is set, the output driver is enabled/disabled when ddov is set/cleared, regardless of the setting of the ddxn register bit. pvoe port value override enable if this signal is set and the output driver is enabled, the port value is controlled by the pvov signal. if pvoe is cleared, and the output driver is enabled, the port value is controlled by the portxn register bit. pvov port value override value if pvoe is set, the port val ue is set to pvov, regardless of the setting of the portxn register bit. ptoe port toggle override enable if ptoe is set, the portxn register bit is inverted. dieoe digital input enable override enable if this bit is set, the digital input enable is controlled by the dieov signal. if this signal is cleared, the digital input enable is determined by mcu state (normal mode, sleep mode). dieov digital input enable override value if dieoe is set, the digital input is enabled/disabled when dieov is set/cleared, regardless of the mcu state (normal mode, sleep mode). di digital input this is the digital i nput to alternate functions. in the figure, the signal is connected to the output of the schmitt trigger but before the synchronizer. unless the digital input is used as a clock source, the module with the alternate function will use its own synchronizer. aio analog input/output this is the analog input/output to/from alternate functions. the signal is connected directly to the pad, and can be used bi-directionally. 53 2543l?avr?08/10 attiny2313 mcu control register ? mcucr ? bit 7 ? pud: pull-up disable when this bit is written to one, the pull-ups in the i/o ports are disabled even if the ddxn and portxn registers are configured to enable the pull-ups ({ddxn, portxn} = 0b01). see ?con- figuring the pin? on page 47 for more details about this feature. alternate functions of port a the port a pins with alternat e functions are as shown in table 5 . alternate functions of port b the port b pins with altern ate functions are shown in table 25 . the alternate pin configuration is as follows: ? usck/scl/pcint7 - port b, bit 7 usck: three-wire mode univer sal serial interface clock. scl: two-wire mode serial clock for usi two-wire mode. pcint7: pin change interrupt source 7. the pb7 pin can serve as an external interrupt source. ? do/pcint6 - port b, bit 6 do: three-wire mode universal serial interface data output. three-wire mode data output over- rides portb6 value and it is driven to the port when data direction bit ddb6 is set (one). however the portb6 bit still controls the pul l-up enabling pull-up, if direction is input and portb6 is set (one). pcint6: pin change interrupt source 6. the pb6 pin can serve as an external interrupt source. bit 7 6 5 4 3 2 1 0 pud sm1 se sm0 isc11 isc10 isc01 isc00 mcucr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 table 24. port a pins alternate functions port pin alternate function pa2 reset, dw pa1 xtal2 pa0 xtal1 table 25. port b pins alternate functions port pin alternate functions pb7 usck/scl/pcint7 pb6 do/pcint6 pb5 di/sda/pcint5 pb4 oc1b/pcint4 pb3 oc1a/pcint3 pb2 oc0a/pcint2 pb1 ain1/pcint1 pb0 ain0/pcint0 54 2543l?avr?08/10 attiny2313 ? di/sda/pcint5 - port b, bit 5 di: three-wire mode universal serial interface data input. three-wire mode does not override normal port functions, so pin must be configured as an input. sda: two-wire mode serial inter- face data. pcint5: pin change interrupt source 5. the pb5 pin can serve as an external interrupt source. ? oc1b/pcint4 ? port b, bit 4 oc1b: output compare match b output: the pb4 pi n can serve as an external output for the timer/counter1 output compare b. the pin has to be configured as an output (ddb4 set (one)) to serve this function. the oc1b pin is also the output pin for the pwm mode timer function. pcint4: pin change interrupt source 4. the pb4 pin can serve as an external interrupt source. ? oc1a/pcint3 ? port b, bit 3 oc1a: output compare match a output: the pb3 pi n can serve as an external output for the timer/counter1 output compare a. the pin has to be configured as an output (ddb3 set (one)) to serve this function. the oc1a pin is also the output pin for the pwm mode timer function. pcint3: pin change interrupt source 3: the pb3 pin can serve as an external interrupt source. ? oc0a/pcint2 ? port b, bit 2 oc0a: output compare match a output. the pb2 pi n can serve as an external output for the timer/counter0 output compare a. the pin has to be configured as an output (ddb2 set (one)) to serve this function. the oc0a pin is also the output pin for the pwm mode timer function. pcint2: pin change interrupt source 2. the pb2 pin can serve as an external interrupt source. ? ain1/pcint1 ? port b, bit 1 ain1: analog comparator negative input . configure the port pin as input with the internal pull-up switched off to avoid the digital port function fr om interfering with the function of the analog comparator. pcint1: pin change interrupt source 1. the pb1 pin can serve as an external interrupt source. ? ain0/pcint0 ? port b, bit 0 ain0: analog comparator positive input. configur e the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the analog comparator. pcint0: pin change interrupt source 0. the pb0 pin can serve as an external interrupt source. table 26 and table 27 relate the alternate functions of port b to the overriding signals shown in figure 25 on page 51 . spi mstr input and spi slave outp ut constitute t he miso signal, while mosi is divided into spi mstr output and spi slave input. 55 2543l?avr?08/10 attiny2313 table 26. overriding signals for altern ate functions in pb7..pb4 signal name pb7/usck/ scl/pcint7 pb6/do/pcint6 pb5/sda/ di/pcint5 pb4/oc1b/ pcint4 puoe usi_two_wire 0 0 0 puov 0 0 0 0 ddoe usi_two_wire 0 usi_two_wire 0 ddov (usi_scl_hold+ p ortb7 )?ddb7 0(sda + portb5 )? ddb5 0 pvoe usi_two_wire ? ddb7 usi_three_wire usi_two_wire ? ddb5 oc1b_pvoe pvov 0 do 0 0oc1b_pvov ptoe usi_ptoe 0 0 0 dieoe (pcint7?pcie) +usisie (pcint6?pcie) (pcint5?pcie) + usisie (pcint4?pcie) dieov 1 1 1 1 di pcint7 input usck input scl input pcint6 input pcint5 input sda input di input pcint4 input aio ? ? ? ? table 27. overriding signals for altern ate functions in pb3..pb0 signal name pb3/oc1a/ pcint3 pb2/oc0a/ pcint2 pb1/ain1/ pcint1 pb0/ain0/ pcint0 puoe 0 0 0 0 puov 0 0 0 0 ddoe 0 0 0 0 ddov 0 0 0 0 pvoe oc1a_pvoe oc0a_pvoe 0 0 pvov oc1a_pvov oc0a_pvov 0 0 ptoe 0 0 0 0 dieoe (pcint3 ? pcie) (pcint2 ? pcie ) (pcint1 ? pcie) (pcint0 ? pcie) dieov 1 1 1 1 di pcint7 input pcint6 input pcint5 input pcint4 input aio ? ? ain1 ain0 56 2543l?avr?08/10 attiny2313 alternate functions of port d the port d pins with alternate functions are shown in table 28 . the alternate pin configuration is as follows: ? icp ? port d, bit 6 icp: timer/counter1 input capture pin. the pd6 pin can act as an input capture pin for timer/counter1 ? oc0b/t1 ? port d, bit 5 oc0b: output compare match b output: the pd5 pin can serve as an external output for the timer/counter0 output compare b. the pin has to be configured as an output (ddd5 set (one)) to serve this function. the oc0b pin is also the output pin for the pwm mode timer function. t1: timer/counter1 external coun ter clock input is enabled by setting (one) the bits cs02 and cs01 in the timer/counter1 control register (tccr1). ? t0 ? port d, bit 4 t0: timer/counter0 external coun ter clock input is enabled by setting (one) the bits cs02 and cs01 in the timer/counter0 control register (tccr0). ? int1 ? port d, bit 3 int1: external interrupt source 1. the pd3 pin can serve as an external interrupt source to the mcu. ? int0/xck/ckout ? port d, bit 2 int0: external interrupt source 0. the pd2 pin can serve as en external interrupt source to the mcu. xck: usart transfer clock used on ly by synchronous transfer mode. ckout: system clock output ? txd ? port d, bit 1 txd: uart data transmitter. ? rxd ? port d, bit 0 rxd: uart data receiver. table 28. port d pins alternate functions port pin alternate function pd6 icp pd5 oc0b/t1 pd4 t0 pd3 int1 pd2 int0/xck/ckout pd1 txd pd0 rxd 57 2543l?avr?08/10 attiny2313 table 29 and table 30 relates the alternate functions of po rt d to the overriding signals shown in figure 25 on page 51 . table 29. overriding signals for alte rnate functions pd7..pd4 signal name pd6/icp pd5/oc1b/t1 pd4/t0 puoe000 puov000 ddoe 0 0 0 ddov 0 0 0 pvoe 0 oc1b_pvoe 0 pvov 0 oc1b_pvov 0 ptoe000 dieoe icp enable t1 enable t0 enable dieov111 di icp input t1 input t0 input aio??ain1 table 30. overriding signals for altern ate functions in pd3..pd0 signal name pd3/int1 pd2/int0/xck/ ckout pd1/txd pd0/rxd puoe 0 0 txd_oe rxd_oe puov 0 0 0 portd0 ? pud ddoe 0 0 txd_oe rxd_en ddov 0 0 1 0 pvoe 0 xcko_pvoe txd_oe 0 pvov 0 xcko_pvov txd_pvov 0 ptoe 0 0 0 0 dieoe int1 enable int0 enable/ xck input enable 00 dieov 1 1 0 0 di int1 input int0 input/ xck input ? rxd input aio ? ? ? ? 58 2543l?avr?08/10 attiny2313 register description for i/o-ports port a data register ? porta port a data direction register ? ddra port a input pins address ? pina port b data register ? portb port b data direction register ? ddrb port b input pins address ? pinb port d data register ? portd port d data direction register ? ddrd port d input pins address ? pind bit 76543210 ?????porta2porta1porta0 porta read/writerrrrrr/wr/wr/w initial value00000000 bit 76543210 ????? dda2 dda1 dda0 ddra read/writerrrrrr/wr/wr/w initial value00000000 bit 76543210 ????? pina2 pina1 pina0 pina read/writerrrrrr/wr/wr/w initial value n/a n/a n/a n/a n/a n/a n/a n/a bit 76543210 portb7 portb6 portb5 portb4 portb3 portb2 portb1 portb0 portb read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 ddb7 ddb6 ddb5 ddb4 ddb3 ddb2 ddb1 ddb0 ddrb read/writer/wr/wr/wr/wr/wr/wr/wr/w initial value00000000 bit 76543210 pinb7 pinb6 pinb5 pinb4 pi nb3 pinb2 pinb1 pinb0 pinb read/writer/wr/wr/wr/wr/wr/wr/wr/w initial value n/a n/a n/a n/a n/a n/a n/a n/a bit 76543210 ? portd6 portd5 portd4 portd3 portd2 portd1 portd0 portd read/write r r/wr/wr/wr/wr/wr/wr/w initial value00000000 bit 76543210 ? ddd6 ddd5 ddd4 ddd3 ddd2 ddd1 ddd0 ddrd read/write r r/wr/wr/wr/wr/wr/wr/w initial value00000000 bit 76543210 ? pind6 pind5 pind4 pind3 pind2 pind1 pind0 pind read/write r r/wr/wr/wr/wr/wr/wr/w initial value n/a n/a n/a n/a n/a n/a n/a n/a 59 2543l?avr?08/10 attiny2313 external interrupts the external interrupts are triggered by the int0 pin, int1 pin or any of the pcint7..0 pins. observe that, if enabled, the interr upts will trigger even if the in t0, int1 or pcint7..0 pins are configured as outputs. this feat ure provides a way of generating a software interrupt. the pin change interrupt pcif will trigger if any enabled pcint7..0 pin toggles. the pcmsk register control which pins contribute to the pin change interrupts. pin change interrupts on pcint7..0 are detected asynchronously. this implies that these interrupts can be used for waking the part also from sleep modes other than idle mode. the int0 and int1 interrupts can be triggered by a falling or rising edge or a low level. this is set up as indicated in the specification for the ?mcu control register ? mcucr? on page 30 . when the int0 or int1 interrupt is enabled and is configured as level triggered, the interrupt will trigger as long as the pin is held low. note that recognition of fa lling or rising edge interrupts on int0 and int1 requires the presence of an i/o clock, described in ?clock systems and their dis- tribution? on page 22 . low level interrupt on int0 and int1 is detected asynchronously. this implies that this interrupt can be used for waking the part from sleep modes other than idle mode. the i/o clock is halted in all sleep modes except idle mode. note that if a level triggered interrupt is used for wake-up from power-down, the required level must be held long enough for the mcu to complete t he wake-up to trigger the level interrupt. if the level disappears before the end of the start-up ti me, the mcu will still wake up, but no inter- rupt will be generated. the start- up time is defined by the su t and cksel fuses as described in ?system clock and clock options? on page 22 . pin change interrupt timing an example of timing of a pin change interrupt is shown in figure 26 . figure 26. mcu control register ? mcucr the external interrupt control register contai ns control bits for interrupt sense control. clk pcint(n) pin_lat pin_sync pcint_in_(n) pcint_syn p cint_setflag pcif pcint(0) pin_sync pcint_syn pin_lat d q le pcint_setflag pc if clk clk pcint(0) in pcmsk(x) pcint_in_(0) 0 x bit 76543210 pud sm1 se sm0 isc11 isc10 isc01 isc00 mcucr 60 2543l?avr?08/10 attiny2313 ? bit 3, 2 ? isc11, isc10: interrupt sense control 1 bit 1 and bit 0 the external interrupt 1 is activated by the exte rnal pin int1 if the sr eg i-flag and the corre- sponding interrupt mask are set. the level and edges on the external int1 pin that activate the interrupt are defined in table 32 . the value on the int1 pin is sampled before detecting edges. if edge or toggle interrupt is selected, pulses that last longer than one clock period will generate an interrupt. shorter pulses are not guaranteed to generate an interrupt. if low level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. ? bit 1, 0 ? isc01, isc00: interrupt sense control 0 bit 1 and bit 0 the external interrupt 0 is activated by the exte rnal pin int0 if the sr eg i-flag and the corre- sponding interrupt mask are set. the level and edges on the external int0 pin that activate the interrupt are defined in table 32 . the value on the int0 pin is sampled before detecting edges. if edge or toggle interrupt is selected, pulses that last longer than one clock period will generate an interrupt. shorter pulses are not guaranteed to generate an interrupt. if low level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. general interrupt mask register ? gimsk ? bit 7 ? int1: external interrupt request 1 enable when the int1 bit is set (one) and the i-bit in th e status register (sreg) is set (one), the exter- nal pin interrupt is enabled. the interrupt sense control1 bits 1/0 (isc11 and isc10) in the mcu control register ? mcucr ? define whether the ex ternal interrupt is activated on rising and/or falling edge of the int1 pin or level sensed. activity on the pin will cause an interrupt request even if int1 is configured as an output. the corresponding interrupt of external interrupt request 1 is executed from the int1 interrupt vector. ? bit 6 ? int0: external interrupt request 0 enable read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 table 31. interrupt 1 sense control isc11 isc10 description 0 0 the low level of int1 generates an interrupt request. 0 1 any logical change on int1 generates an interrupt request. 1 0 the falling edge of int1 generates an interrupt request. 1 1 the rising edge of int1 generates an interrupt request. table 32. interrupt 0 sense control isc01 isc00 description 0 0 the low level of int0 generates an interrupt request. 0 1 any logical change on int0 generates an interrupt request. 1 0 the falling edge of int0 generates an interrupt request. 1 1 the rising edge of int0 generates an interrupt request. bit 76543210 int1 int0 pcie ? ? ? ? ?gimsk read/write r/w r/w r/w r r r r r initial value 0 0 0 0 0 0 0 0 61 2543l?avr?08/10 attiny2313 when the int0 bit is set (one) and the i-bit in th e status register (sreg) is set (one), the exter- nal pin interrupt is enabled. the interrupt sense control0 bits 1/0 (isc01 and isc00) in the mcu control register ? mcucr ? define whether the ex ternal interrupt is activated on rising and/or falling edge of the int0 pin or level sensed. activity on the pin will cause an interrupt request even if int0 is configured as an output. the corresponding interrupt of external interrupt request 0 is executed from the int0 interrupt vector. ? bit 5 ? pcie: pin change interrupt enable when the pcie bit is set (one) and the i-bit in the status register (sreg) is set (one), pin change interrupt 1 is enabled. any change on any enabl ed pcint7..0 pin will cause an interrupt. the corresponding interrupt of pin change interr upt request is executed from the pci interrupt vector. pcint7..0 pins are enabled individually by the pcmsk register. external interrupt flag register ? eifr ? bit 7 ? intf1: external interrupt flag 1 when an edge or logic change on the int1 pin triggers an interrupt request, intf1 becomes set (one). if the i-bit in sreg and the int1 bit in gimsk are set (o ne), the mcu will jump to the cor- responding interrupt vector. the flag is cleared when the interrupt routine is executed. alternatively, the flag can be clea red by writing a logical one to it. this flag is always cleared when int1 is configured as a level interrupt. ? bit 6 ? intf0: external interrupt flag 0 when an edge or logic change on the int0 pin triggers an interrupt request, intf0 becomes set (one). if the i-bit in sreg and the int0 bit in gimsk are set (o ne), the mcu will jump to the cor- responding interrupt vector. the flag is cleared when the interrupt routine is executed. alternatively, the flag can be clea red by writing a logical one to it. this flag is always cleared when int0 is configured as a level interrupt. ? bit 5 ? pcif: pin change interrupt flag when a logic change on any pcint7..0 pin triggers an interrupt request, pcif becomes set (one). if the i-bit in sreg and the pcie bit in gimsk are set (one), the mcu will jump to the cor- responding interrupt vector. the flag is cleared when the interrupt routine is executed. alternatively, the flag can be cleared by writing a logical one to it. pin change mask register ? pcmsk ? bit 7..0 ? pcint7..0: pin change enable mask 7..0 each pcint7..0-bit selects whether pin change interrupt is enabled on the corresponding i/o pin. if pcint7..0 is set and the pcie bit in gim sk is set, pin change interrupt is enabled on the corresponding i/o pin. if pcint7 ..0 is cleared, pin change interrupt on the corresponding i/o pin is disabled. bit 76543210 intf1 intf0 pcif ? ? ? ? ?eifr read/write r/w r/w r/w r r r r r initial value 0 0 0 0 0 0 0 0 bit 76543210 pcint7 pcint6 pcint5 pcint4 pcint3 pcint2 pcint1 pcint0 pcmsk read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 62 2543l?avr?08/10 attiny2313 8-bit timer/counter0 with pwm timer/counter0 is a general purpose 8-bit time r/counter module, with two independent output compare units, and with pwm support. it allows accurate program execution timing (event man- agement) and wave generation. the main features are: ? two independent output compare units ? double buffered output compare registers ? clear timer on compare match (auto reload) ? glitch free, phase correct pulse width modulator (pwm) ? variable pwm period ? frequency generator ? three independent interrupt sources (tov0, ocf0a, and ocf0b) overview a simplified block diagram of the 8-bit timer/counter is shown in figure 27 . for the actual place- ment of i/o pins, refer to ?pinout attiny2313? on page 2 . cpu accessible i/o registers, including i/o bits and i/o pins, are shown in bold. the device-specific i/o register and bit loca- tions are listed in the ?8-bit timer/counter register description? on page 73 . figure 27. 8-bit timer/counter block diagram registers the timer/counter (tcnt0) and output compare registers (ocr0a and ocr0b) are 8-bit registers. interrupt request (abbreviated to int.req . in the figure) signals are all visible in the timer interrupt flag register (tifr). all interrup ts are individually masked with the timer inter- rupt mask register (timsk). tifr and timsk are not shown in the figure. the timer/counter can be clocked internally, via th e prescaler, or by an external clock source on the t0 pin. the clock select logic block contro ls which clock source and edge the timer/counter uses to increment (or decrement) its value. th e timer/counter is inactive when no clock source is selected. the output from th e clock select logic is referred to as the timer clock (clk t0 ). the double buffered output compare registers (ocr0a and ocr0b) is compared with the timer/counter value at all times. the result of the compare can be used by the waveform gen- erator to generate a pwm or variable frequency output on the output compare pins (oc0a and oc0b). see ?output compare unit? on page 64. for details. the comp are match event will also set the compare flag (ocf0a or ocf0b) which can be used to generate an output compare interrupt request. clock select timer/counter data bus ocrna ocrnb = = tcntn waveform generation waveform generation ocfna ocfnb = fixed top value control logic = 0 top bottom count clear direction tovn (int.req.) ocfna (int.req.) ocfnb (int.req.) tccrna tccrnb tn edge detector ( from prescaler ) clk tn 63 2543l?avr?08/10 attiny2313 definitions many register and bit references in this section are written in general form. a lower case ?n? replaces the timer/counter number, in this case 0. a lower case ?x? replaces the output com- pare unit, in this case compare unit a or comp are unit b. however, when using the register or bit defines in a program, the precise form must be used, i.e., tcnt0 for accessing timer/counter0 counter value and so on. the definitions in table 33 are also used extensively throughout the document. timer/counter clock sources the timer/counter can be clocked by an internal or an external clock source. the clock source is selected by the clock select logic which is controlled by the clock select (cs02:0) bits located in the timer/counter control register (tccr0b). for details on clock sources and pres- caler, see ?timer/counter0 and timer/counter1 prescalers? on page 80 . counter unit the main part of the 8-bit timer/counter is the programmable bi-directional counter unit. figure 28 shows a block diagram of the counter and its surroundings. figure 28. counter unit block diagram signal description (internal signals): count increment or decrement tcnt0 by 1. direction select between increment and decrement. clear clear tcnt0 (set all bits to zero). clk t n timer/counter clock, referred to as clk t0 in the following. top signalize that tcnt0 ha s reached maximum value. bottom signalize that tcnt0 has re ached minimum value (zero). table 33. definitions bottom the counter reaches the bottom when it becomes 0x00. max the counter reaches its maximum when it becomes 0xff (decimal 255). top the counter reaches the top when it becomes equal to the highest value in the count sequence. the top value can be assigned to be the fixed value 0xff (max) or the value stored in the ocr0a register. the assignment is dependent on the mode of operation. data b u s tcntn control logic count tovn (int.req.) clock select top tn edge detector ( from prescaler ) clk tn bottom direction clear 64 2543l?avr?08/10 attiny2313 depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clk t0 ). clk t0 can be generated from an external or internal clock source, selected by the clock select bits (cs02:0). w hen no clock source is selected (cs02:0 = 0) the timer is stopped. however, the tcnt0 value can be accessed by the cpu, regardless of whether clk t0 is present or not. a cpu write overrides (has priority over) all counter clear or count operations. the counting sequence is determined by the se tting of the wgm01 and wgm00 bits located in the timer/counter control regist er (tccr0a) and the wgm02 bit located in the timer/counter control register b (tccr0b). there are clos e connections between how the counter behaves (counts) and how waveforms are generated on the output compare output oc0a. for more details about advanced counting s equences and waveform generation, see ?modes of opera- tion? on page 94 . the timer/counter overflow flag (tov0) is set a ccording to the mode of operation selected by the wgm01:0 bits. tov0 can be us ed for generating a cpu interrupt. output compare unit the 8-bit comparator continuously compares tcnt0 with the output compare registers (ocr0a and ocr0b). whenever tcnt0 equals ocr0 a or ocr0b, the comparator signals a match. a match will set the output compare flag (ocf0a or ocf0 b) at the next timer clock cycle. if the corresponding interrupt is enabled, the output compare flag generates an output compare interrupt. the output compare flag is aut omatically cleared when the interrupt is exe- cuted. alternatively, the flag can be cleared by software by writing a logical one to its i/o bit location. the waveform generator uses the matc h signal to generate an output according to operating mode set by the wgm02:0 bits and compare output mode (com0x1:0) bits. the max and bottom signals are used by the waveform generator for handling the special cases of the extreme values in some modes of operation (see ?modes of operation? on page 94 ). figure 29 shows a block diagram of the output compare unit. figure 29. output compare unit, block diagram ocfn x (int.req.) = (8-bit comparator ) ocrnx ocnx data bus tcntn wgmn1:0 waveform generator top focn comnx1:0 bottom 65 2543l?avr?08/10 attiny2313 the ocr0x registers are double buffered when using any of the pulse width modulation (pwm) modes. for the normal and clear timer on compare (ctc) modes of operation, the dou- ble buffering is disabled. the double buffering synchronizes the update of the ocr0x compare registers to either top or bottom of the counting sequence. the synchronization prevents the occurrence of odd-length, non-symmetrical pwm pulses, thereby making the output glitch-free. the ocr0x register access may seem complex, but this is not case. when the double buffering is enabled, the cpu has access to the ocr0x buffer register, and if double buffering is dis- abled the cpu will access the ocr0x directly. force output compare in non-pwm waveform generation modes, the matc h output of the comparator can be forced by writing a one to the force outp ut compare (foc0x) bit. forcin g compare match will not set the ocf0x flag or reload/clear the timer, but the oc0x pin will be updated as if a real compare match had occurred (the com0x1:0 bits settings de fine whether the oc0x pin is set, cleared or toggled). compare match blocking by tcnt0 write all cpu write operations to the tcnt0 register will block any compare ma tch that occur in the next timer clock cycle, even when the timer is stopped. this feat ure allows ocr0x to be initial- ized to the same value as tcnt0 without trigge ring an interrupt when the timer/counter clock is enabled. using the output compare unit since writing tcnt0 in any mo de of operation will block all compare matches for one timer clock cycle, there are risks involved when ch anging tcnt0 when using the output compare unit, independently of whether the timer/counter is running or not. if the value written to tcnt0 equals the ocr0x value, the compare match will be missed, resulting in incorrect waveform generation. similarly, do not write the tcnt0 value equal to bottom when the counter is down-counting. the setup of the oc0x should be performed before setting the data direction register for the port pin to output. the easiest way of setting the oc0x value is to use the force output com- pare (foc0x) strobe bits in normal mode. the oc0x registers keep their values even when changing between waveform generation modes. be aware that the com0x1:0 bits are not doubl e buffered together with the compare value. changing the com0x1:0 bits will take effect immediately. compare match output unit the compare output mode (com0x1:0) bits ha ve two functions. the waveform generator uses the com0x1:0 bits for defining the output co mpare (oc0x) state at the next compare match. also, the com0x1:0 bi ts control the oc0x pin output source. figure 30 shows a simplified sche- matic of the logic affected by the com0x1:0 bit setting. the i/o registers, i/o bits, and i/o pins in the figure are shown in bold. only the parts of the general i/o port control registers (ddr and port) that are affected by the com0x1:0 bits are shown. when referring to the oc0x state, the reference is for the internal oc0x re gister, not the oc0x pin. if a system reset occur, the oc0x register is reset to ?0?. 66 2543l?avr?08/10 attiny2313 figure 30. compare match output unit, schematic the general i/o port function is overridden by the output compare (oc0x) from the waveform generator if either of the com0x1:0 bits are se t. however, the oc0x pin direction (input or out- put) is still controlled by the da ta direction register (ddr) for th e port pin. the data direction register bit for the oc0x pin (ddr_oc0x) must be set as output before th e oc0x value is visi- ble on the pin. the port over ride function is independent of the waveform generation mode. the design of the output compare pin logic allows initialization of the oc 0x state before the out- put is enabled. note that some com0x1:0 bi t settings are reserved for certain modes of operation. see ?8-bit timer/counter register description? on page 73. compare output mode and waveform generation the waveform generator uses the com0x1:0 bits differently in normal, ctc, and pwm modes. for all modes, setting the com0x1:0 = 0 tell s the waveform generator that no action on the oc0x register is to be perfo rmed on the next compare match. for compare output actions in the non-pwm modes refer to figure 29 on page 64 . for fast pwm mode, refer to table 26 on page 55 , and for phase correct pwm refer to table 27 on page 55 . a change of the com0x1:0 bits state will have effe ct at the first compare match after the bits are written. for non-pwm modes, the action can be fo rced to have immediate effect by using the foc0x strobe bits. modes of operation the mode of operation, i.e., t he behavior of the timer/counter and the output compare pins, is defined by the combination of the waveform generation mode (wgm02:0) and compare output mode (com0x1:0) bits. the compare output mode bits do not affect the counting sequence, while the waveform generation mode bits do. the com0x1:0 bits control whether the pwm out- put generated should be inverted or not (inverted or non-inverted pwm). for non-pwm modes the com0x1:0 bits control whether the output should be set, cleared, or toggled at a compare match ( see ?compare match output unit? on page 65. ). for detailed timing information refer to figure 34 , figure 35 , figure 36 and figure 37 in ?timer/counter timing diagrams? on page 71 . normal mode the simplest mode of operation is the normal mode (wgm02:0 = 0). in this mode the counting direction is always up (incre menting), and no counter clear is performed. the counter simply overruns when it passes its maxi mum 8-bit value (top = 0xff) and then restarts from the bot- tom (0x00). in normal o peration the timer/counter overflow flag (tov0) will be set in the same port ddr dq dq ocn pin ocnx dq waveform generator comnx1 comnx0 0 1 data bus focn clk i/o 67 2543l?avr?08/10 attiny2313 timer clock cycle as the tcnt0 becomes zero. the tov0 flag in this case behaves like a ninth bit, except that it is only set, not cleared. ho wever, combined with the timer overflow interrupt that automatically clears the tov0 flag, the timer resolution can be increased by software. there are no special cases to consider in the normal mode, a new counter value can be written anytime. the output compare unit can be used to generate interrupts at some given time. using the out- put compare to generate waveforms in normal mode is not recommended, since this will occupy too much of the cpu time. clear timer on compare match (ctc) mode in clear timer on compare or ctc mode (wgm 02:0 = 2), the ocr0a register is used to manipulate the counter resolution . in ctc mode the counter is cleared to zero when the counter value (tcnt0) matches the ocr0a. the ocr0a de fines the top value fo r the counter, hence also its resolution. this mode allows greater control of the compare match output frequency. it also simplifies the operation of counting external events. the timing diagram for the ctc mode is shown in figure 31 . the counter value (tcnt0) increases until a compare match occurs between tcnt0 and ocr0a, and then counter (tcnt0) is cleared. figure 31. ctc mode, timing diagram an interrupt can be generated each time the c ounter value reaches the top value by using the ocf0a flag. if the interrupt is enabled, the interrupt handler routine can be used for updating the top value. however, changing top to a va lue close to bottom when the counter is run- ning with none or a low prescaler value must be done with care since the ctc mode does not have the double buffering feature. if the new value written to ocr0a is lower than the current value of tcnt0, the counter will miss the compar e match. the counter will then have to count to its maximum value (0xff) and wrap around starting at 0x00 before the compare match can occur. for generating a waveform output in ctc mode, t he oc0a output can be set to toggle its logical level on each compare match by setting the compare output mode bits to toggle mode (com0a1:0 = 1). the oc0a value will not be visible on the port pin unless the data direction for the pin is set to output. the waveform ge nerated will have a ma ximum frequency of f oc0 = f clk_i/o /2 when ocr0a is set to zero (0x00). the waveform frequency is defined by the following equation: the n variable represents the prescale factor (1, 8, 64, 256, or 1024). t cntn o cn ( toggle) ocnx interrupt flag set 1 4 p eriod 2 3 (comnx1:0 = 1) f ocnx f clk_i/o 2 n 1 ocrnx + () ?? ------------------------------------------------- - = 68 2543l?avr?08/10 attiny2313 as for the normal mode of operat ion, the tov0 flag is set in the same timer clock cycle that the counter counts fr om max to 0x00. fast pwm mode the fast pulse width modulation or fast pwm mode (wgm02:0 = 3 or 7) provides a high fre- quency pwm waveform generation option. the fa st pwm differs from the other pwm option by its single-slope operation. the c ounter counts from bottom to top then restarts from bot- tom. top is defined as 0xff when wgm2:0 = 3, and ocr0a when wgm2:0 = 7. in non- inverting compare output mode, the output compare (oc0x) is cleared on the compare match between tcnt0 and ocr0x, and set at bottom. in inverting compare output mode, the out- put is set on compare match and cleared at bottom. due to the single-slope operation, the operating frequency of the fast pwm mode can be twice as high as the phase correct pwm mode that use dual-slope operation. this high frequency makes the fast pwm mode well suited for power regulation, rectification, and dac app lications. high frequency a llows physically small sized external components (coils, capacitors), and therefore reduces total system cost. in fast pwm mode, the counter is incremented until the counter value matches the top value. the counter is then cleared at the following timer clock cycle. the timing diagram for the fast pwm mode is shown in figure 30 . the tcnt0 value is in the timing diagram shown as a histo- gram for illustrating the single-s lope operation. the diagram includes non- inverted and inverted pwm outputs. the small horizontal line marks on the tcnt0 slopes represent compare matches between ocr0x and tcnt0. figure 32. fast pwm mode, timing diagram the timer/counter overflow flag (tov0) is set each time the counter re aches top. if the inter- rupt is enabled, the interrupt handler routi ne can be used for updating the compare value. in fast pwm mode, the compare unit allows generation of pwm waveforms on the oc0x pins. setting the com0x1:0 bits to two will produce a non-inverted pwm and an inverted pwm output can be generated by setting the com0x1:0 to th ree: setting the com0a1:0 bits to one allows the ac0a pin to toggle on compare matches if t he wgm02 bit is set. this option is not available for the oc0b pin (see table 26 on page 55 ). the actual oc0x value will only be visible on the port pin if the data direction fo r the port pin is set as output. the pwm waveform is generated by setting (or clearing) the oc0x register at the compare match between ocr0x and tcnt0, and clearing (or setting) the oc0x r egister at the timer clock c ycle the counter is cleared (changes from top to bottom). t cntn ocrnx update and tovn interrupt flag set 1 p eriod 2 3 o cn o cn (comnx1:0 = 2) (comnx1:0 = 3) ocrnx interrupt flag se t 4 5 6 7 69 2543l?avr?08/10 attiny2313 the pwm frequency for the output can be calculated by the following equation: the n variable represents the prescale factor (1, 8, 64, 256, or 1024). the extreme values for the ocr0a register represents special cases when generating a pwm waveform output in the fast pwm mode. if t he ocr0a is set equal to bottom, the output will be a narrow spike for each max+1 timer clock cycle. setting the ocr0a equal to max will result in a constantly high or low output (depending on the polarity of the out put set by the com0a1:0 bits.) a frequency (with 50% duty cycle) waveform out put in fast pwm mode can be achieved by set- ting oc0x to toggle its logical level on each compare match (com0x1:0 = 1). the waveform generated will have a maximum frequency of f oc0 = f clk_i/o /2 when ocr0a is set to zero. this feature is similar to the oc0a toggle in ctc mo de, except the double buff er feature of the out- put compare unit is enabled in the fast pwm mode. phase correct pwm mode the phase correct pwm mode (wgm02:0 = 1 or 5) provides a high resolution phase correct pwm waveform generation option. the phase correct pwm mode is based on a dual-slope operation. the counter counts repeatedly from bottom to top and then from top to bot- tom. top is defined as 0xff when wgm2:0 = 1, and ocr0a when wgm2:0 = 5. in non- inverting compare output mode, the output compare (oc0x) is cleared on the compare match between tcnt0 and ocr0x while upcounting, and set on the compare match while down- counting. in inverting output compare mode, the operation is inverted. the dual-slope operation has lower maximum operation frequency than single slope operation. however, due to the sym- metric feature of the dual-slope pwm modes, t hese modes are preferred for motor control applications. in phase correct pwm mode the counter is incremented until the counter value matches top. when the counter reaches top, it changes the count direction. the tcnt0 value will be equal to top for one timer clock cycle. the timing diagram for the phase correct pwm mode is shown on figure 33 . the tcnt0 value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. the diag ram includes non-inverted and in verted pwm outputs. the small horizontal line marks on the tcnt0 slopes represent compare matches between ocr0x and tcnt0. f ocnxpwm f clk_i/o n 256 ? ------------------ = 70 2543l?avr?08/10 attiny2313 figure 33. phase correct pwm mode, timing diagram the timer/counter overflow flag (tov0) is set each time the counter reaches bottom. the interrupt flag can be used to g enerate an interrupt each time the counter reaches the bottom value. in phase correct pwm mode, the compare unit allows generation of pwm waveforms on the oc0x pins. setting the com0x1:0 bits to two will produce a non-inverted pwm. an inverted pwm output can be generated by setting the com0x1:0 to three: setting the com0a0 bits to one allows the oc0a pin to toggle on compare ma tches if the wgm02 bit is set. this option is not available for the oc0b pin (see table 27 on page 55 ). the actual oc0x value will only be visible on the port pin if the data direction for the port pin is set as output. the pwm waveform is generated by clearing (or setting) the oc0x register at the compare match between ocr0x and tcnt0 when the counter increments, and setti ng (or clearing) the oc0x register at com- pare match between ocr0x and tcnt0 when the counter decrements. the pwm frequency for the output when using phase correct pwm c an be calculated by the following equation: the n variable represents the prescale factor (1, 8, 64, 256, or 1024). the extreme values for the ocr0a register represent special cases when generating a pwm waveform output in the phase correct pwm mo de. if the ocr0a is set equal to bottom, the output will be continuously low an d if set equal to max the output will be continuously high for non-inverted pwm mode. for in verted pwm the output will have the opposite logic values. at the very start of period 2 in figure 33 ocn has a transition from high to low even though there is no compare match. the point of this transition is to guarantee symmetry around bottom. there are two cases that give a transition without compare match. ? ocr0a changes its value from max, like in figure 33 . when the ocr0a value is max the ocn pin value is the same as the result of a down-counting compare match. to ensure symmetry around bottom the ocn value at max must correspond to the result of an up- counting compare match. tovn interrupt flag set ocnx interrupt flag set 1 2 3 tcntn period ocn ocn (comnx1:0 = 2) (comnx1:0 = 3) ocrnx update f ocnxpcpwm f clk_i/o n 510 ? ------------------ = 71 2543l?avr?08/10 attiny2313 ? the timer starts counting from a value higher than the one in ocr0a, and for that reason misses the compare match and hence the ocn change that would have happened on the way up. timer/counter timing diagrams the timer/counter is a synchronous design and the timer clock (clk t0 ) is therefore shown as a clock enable signal in the following figures. the figures include information on when interrupt flags are set. figure 34 contains timing data for basic timer/counter operation. the figure shows the count sequence close to the max value in all modes other than phase correct pwm mode. figure 34. timer/counter timing diagram, no prescaling figure 34 shows the same timing data, but with the prescaler enabled. figure 35. timer/counter timing diagram, with prescaler (f clk_i/o /8) figure 36 shows the setting of ocf0b in all mode s and ocf0a in all modes except ctc mode and pwm mode, where ocr0a is top. figure 36. timer/counter timing diagram, se tting of ocf0x, with prescaler (f clk_i/o /8) figure 37 shows the setting of ocf0a and the clearing of tcnt0 in ctc mode and fast pwm mode where ocr0a is top. clk tn (clk i/o /1) tovn clk i/o tcntn max - 1 max bottom bottom + 1 tovn tcntn max - 1 max bottom bottom + 1 clk i/o clk tn (clk i/o /8) ocfnx ocrnx tcntn ocrnx value ocrnx - 1 ocrnx ocrnx + 1 ocrnx + 2 clk i/o clk tn (clk i/o /8) 72 2543l?avr?08/10 attiny2313 figure 37. timer/counter timing diagra m, clear timer on compare match mode, with pres- caler (f clk_i/o /8) ocfnx ocrnx tcntn (ctc) top top - 1 top bottom bottom + 1 clk i/o clk tn (clk i/o /8) 73 2543l?avr?08/10 attiny2313 8-bit timer/counter register description timer/counter control register a ? tccr0a ? bits 7:6 ? com0a1:0: compare match output a mode these bits control the output compare pin (oc0a) behavior. if one or both of the com0a1:0 bits are set, the oc0a output overrides the normal po rt functionality of the i/o pin it is connected to. however, note that the data direction r egister (ddr) bit corresponding to the oc0a pin must be set in order to enable the output driver. when oc0a is connected to the pin, the function of the com0a1:0 bits depends on the wgm02:0 bit setting. table 34 shows the com0a1:0 bit functi onality when the wgm02:0 bits are set to a normal or ctc mode (non-pwm). table 35 shows the com0a1:0 bit functionality when the wgm01:0 bits are set to fast pwm mode. note: 1. a special case occurs when ocr0a equals top and com0a1 is set. in this case, the com- pare match is ignored, but the set or clear is done at top. see ?fast pwm mode? on page 68 for more details. bit 7 6 5 4 3 2 1 0 com0a1 com0a0 com0b1 com0b0 ? ? wgm01 wgm00 tccr0a read/write r/w r/w r/w r/w r r r/w r/w initial value 0 0 0 0 0 0 0 0 table 34. compare output mode, non-pwm mode com0a1 com0a0 description 0 0 normal port operation, oc0a disconnected. 0 1 toggle oc0a on compare match 1 0 clear oc0a on compare match 1 1 set oc0a on compare match table 35. compare output mode, fast pwm mode (1) com0a1 com0a0 description 0 0 normal port operation, oc0a disconnected. 0 1 wgm02 = 0: normal port o peration, oc0a disconnected. wgm02 = 1: toggle oc0a on compare match. 1 0 clear oc0a on compare match, set oc0a at top 1 1 set oc0a on compare match, clear oc0a at top 74 2543l?avr?08/10 attiny2313 table 36 shows the com0a1:0 bit functionality when the wgm02:0 bits are set to phase correct pwm mode. note: 1. a special case occurs when ocr0a equals top and com0a1 is set. in this case, the com- pare match is ignored, but the set or clear is done at top. see ?phase correct pwm mode? on page 69 for more details. ? bits 5:4 ? com0b1:0: compare match output b mode these bits control the output compare pin (oc0b) behavior. if one or both of the com0b1:0 bits are set, the oc0b output overrides the normal po rt functionality of the i/o pin it is connected to. however, note that the data direction r egister (ddr) bit corresponding to the oc0b pin must be set in order to enable the output driver. when oc0b is connected to the pin, the function of the com0b1:0 bits depends on the wgm02:0 bit setting. table 37 shows the com0a1:0 bit functi onality when the wgm02:0 bits are set to a normal or ctc mode (non-pwm). table 38 shows the com0b1:0 bit functionality when the wgm02:0 bits are set to fast pwm mode. note: 1. a special case occurs when ocr0b equals top and com0b1 is set. in this case, the com- pare match is ignored, but the set or clear is done at top. see ?fast pwm mode? on page 68 for more details. table 36. compare output mode, phase correct pwm mode (1) com0a1 com0a0 description 0 0 normal port operation, oc0a disconnected. 0 1 wgm02 = 0: normal port o peration, oc0a disconnected. wgm02 = 1: toggle oc0a on compare match. 1 0 clear oc0a on compare match when up-counting. set oc0a on compare match when down-counting. 1 1 set oc0a on compare match when up-counting. clear oc0a on compare match when down-counting. table 37. compare output mode, non-pwm mode com0b1 com0b0 description 0 0 normal port operation, oc0b disconnected. 0 1 toggle oc0b on compare match 1 0 clear oc0b on compare match 1 1 set oc0b on compare match table 38. compare output mode, fast pwm mode (1) com0b1 com0b0 description 0 0 normal port operation, oc0b disconnected. 01reserved 1 0 clear oc0b on compare match, set oc0b at top 1 1 set oc0b on compare match, clear oc0b at top 75 2543l?avr?08/10 attiny2313 table 39 shows the com0b1:0 bit functionality when the wgm02:0 bits are set to phase correct pwm mode. note: 1. a special case occurs when ocr0b equals top and com0b1 is set. in this case, the com- pare match is ignored, but the set or clear is done at top. see ?phase correct pwm mode? on page 69 for more details. ? bits 3, 2 ? res: reserved bits these bits are reserved bits in the attiny2313 and will a lways read as zero. ? bits 1:0 ? wgm01:0: waveform generation mode combined with the wgm02 bit found in the tccr0b register, these bits control the counting sequence of the counter, the source for maximu m (top) counter value, and what type of wave- form generation to be used, see table 40 . modes of operation suppor ted by the timer/counter unit are: normal mode (counter), clear time r on compare match (ctc) mode, and two types of pulse width modulation (pwm) modes (see ?modes of operation? on page 66 ). notes: 1. max = 0xff 2. bottom = 0x00 table 39. compare output mode, phase correct pwm mode (1) com0b1 com0b0 description 0 0 normal port operation, ocr0b disconnected. 01reserved 1 0 clear orc0b on compare match when up-counting. set ocr0b on compare match when down-counting. 1 1 set ocr0b on compare match when up-counting. clear ocr0b on compare match when down-counting. table 40. waveform generation mode bit description mode wgm2 wgm1 wgm0 timer/count er mode of operation top update of ocrx at tov flag set on (1)(2) 0 0 0 0 normal 0xff immediate max 1 0 0 1 pwm, phase correct 0xff top bottom 2 0 1 0 ctc ocr0a immediate max 3 0 1 1 fast pwm 0xff top max 4100reserved?? ? 5 1 0 1 pwm, phase correct ocr0a top bottom 6110reserved?? ? 7 1 1 1 fast pwm ocr0a top top 76 2543l?avr?08/10 attiny2313 timer/counter control register b ? tccr0b ? bit 7 ? foc0a: force output compare a the foc0a bit is only active when the wgm bits specify a non-pwm mode. however, for ensuring compatibility with future devices, this bit must be set to zero when tccr0b is written when operating in pwm mode. when writing a logical one to the foc0a bit, an immediate compare match is forced on the wa veform generation unit . the oc0a output is changed according to its com0a1:0 bits setting. note that the foc0a bit is implemented as a strobe. therefore it is the value present in the com0a1:0 bits that determines the effect of the forced compare. a foc0a strobe will not generate any interrupt, nor will it clear the timer in ctc mode using ocr0a as top. the foc0a bit is always read as zero. ? bit 6 ? foc0b: force output compare b the foc0b bit is only active when the wgm bits specify a non-pwm mode. however, for ensuring compatibility with future devices, this bit must be set to zero when tccr0b is written when operating in pwm mode. when writing a logical one to the foc0b bit, an immediate compare match is forced on the wa veform generation unit . the oc0b output is changed according to its com0b1:0 bits setting. note that the foc0b bit is implemented as a strobe. therefore it is the value present in the com0b1:0 bits that determines the effect of the forced compare. a foc0b strobe will not generate any interrupt, nor will it clear the timer in ctc mode using ocr0b as top. the foc0b bit is always read as zero. ? bits 5:4 ? res: reserved bits these bits are reserved bits in the attiny2313 and will a lways read as zero. ? bit 3 ? wgm02: waveform generation mode see the description in the ?timer/counter control register a ? tccr0a? on page 73 . ? bits 2:0 ? cs02:0: clock select the three clock select bits select the clock source to be used by the timer/counter. see table 41 on page 77 . bit 7 6 5 4 3 2 1 0 foc0a foc0b ? ? wgm02 cs02 cs01 cs00 tccr0b read/write w w r r r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 77 2543l?avr?08/10 attiny2313 if external pin modes are used for the timer/counter0, transitions on the t0 pin will clock the counter even if the pin is configured as an outpu t. this feature allows software control of the counting. timer/counter register ? tcnt0 the timer/counter register gives direct ac cess, both for read and write operations, to the timer/counter unit 8-bit counter. writing to the tcnt0 register blocks (removes) the compare match on the following timer clock. modifying t he counter (tcnt0) while the counter is running, introduces a risk of missing a compare match between tcnt0 and the ocr0x registers. output compare register a ? ocr0a the output compare register a contains an 8-bi t value that is conti nuously compared with the counter value (tcnt0). a match can be used to generate an output compare interrupt, or to generate a waveform output on the oc0a pin. output compare register b ? ocr0b the output compare register b contains an 8-bi t value that is conti nuously compared with the counter value (tcnt0). a match can be used to generate an output compare interrupt, or to generate a waveform output on the oc0b pin. table 41. clock select bit description cs02 cs01 cs00 description 0 0 0 no clock source (timer/counter stopped) 001clk i/o /(no prescaling) 010clk i/o /8 (from prescaler) 011clk i/o /64 (from prescaler) 100clk i/o /256 (from prescaler) 101clk i/o /1024 (from prescaler) 1 1 0 external clock source on t0 pin. clock on falling edge. 1 1 1 external clock source on t0 pin. clock on rising edge. bit 76543210 tcnt0[7:0] tcnt0 read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 ocr0a[7:0] ocr0a read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 ocr0b[7:0] ocr0b read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 78 2543l?avr?08/10 attiny2313 timer/counter interrupt mask register ? timsk ? bit 4 ? res: reserved bit this bit is reserved bit in the at tiny2313 and will always read as zero. ? bit 2 ? ocie0b: timer/counter0 output compare match b interrupt enable when the ocie0b bit is written to one, and the i-bit in the status register is set, the timer/counter compare match b interrupt is enab led. the corresponding interrupt is executed if a compare match in timer/counter occurs, i.e., when the ocf0b bi t is set in the timer/counter interrupt flag register ? tifr. ? bit 1 ? toie0: timer/counter0 overflow interrupt enable when the toie0 bit is written to one, and t he i-bit in the status register is set, the timer/counter0 overflow interr upt is enabled. the corresponding interrupt is executed if an overflow in timer/counter0 occu rs, i.e., when the tov0 bit is set in the timer/counter 0 inter- rupt flag register ? tifr. ? bit 0 ? ocie0a: timer/counter0 output compare match a interrupt enable when the ocie0a bit is written to one, and th e i-bit in the status register is set, the timer/counter0 compare match a interrupt is enabled. the corresponding interrupt is executed if a compare match in timer/counter0 occurs, i.e., when the ocf0a bit is set in the timer/counter 0 interrupt flag register ? tifr. timer/counter interrupt flag register ? tifr ? bit 4 ? res: reserved bit this bit is reserved bit in the at tiny2313 and will always read as zero. ? bit 2 ? ocf0b: output compare flag 0 b the ocf0b bit is set when a compare match occurs between the timer/counter and the data in ocr0b ? output compare register0 b. ocf0b is cleared by hardware when executing the cor- responding interrupt handling vector. alternatively, ocf0b is cleared by writing a logic one to the flag. when the i-bit in sreg, ocie0b (tim er/counter compare b match interrupt enable), and ocf0b are set, the timer/counter compare match interrupt is executed. ? bit 1 ? tov0: timer/counter0 overflow flag the bit tov0 is set when an overflow occurs in timer/counter0. tov0 is cleared by hardware when executing the corresponding interrupt handling vector. alternatively, tov0 is cleared by writing a logic one to the flag. when the sreg i-bit, toie0 (timer/count er0 overflow interrupt enable), and tov0 are set, the timer/co unter0 overflow interrupt is executed. the setting of this flag is dependent of the wgm02:0 bit setting. refer to table 40 , ?waveform generation mode bit description? on page 75 . ? bit 0 ? ocf0a: output compare flag 0 a the ocf0a bit is set when a compare match oc curs between the timer/counter0 and the data in ocr0a ? output compare register0 a. ocf0a is cleared by hardware when executing the corresponding interrupt handling vector. alternativ ely, ocf0a is cleared by writing a logic one to bit 76543210 toie1 ocie1a ocie1b ? icie1 ocie0b toie0 ocie0a timsk read/write r/w r/w r/w r r/w r/w r/w r/w initial value00000000 bit 76543210 tov1 ocf1a ocf1b ? icf1 ocf0b tov0 ocf0a tifr read/write r/w r/w r/w r r/w r/w r/w r/w initial value00000000 79 2543l?avr?08/10 attiny2313 the flag. when the i-bit in sreg, ocie0a (t imer/counter0 compare match interrupt enable), and ocf0a are set, the timer/counter0 co mpare match interrupt is executed. 80 2543l?avr?08/10 attiny2313 timer/counter0 and timer/counter1 prescalers timer/counter1 and time r/counter0 share the same prescale r module, but the timer/counters can have different prescaler settings. the description below applies to both timer/counter1 and timer/counter0. internal clock source the timer/counter can be clocked directly by the system clock (by setting the csn2:0 = 1). this provides the fastest operation, with a maximum timer/counter clock frequency equal to system clock frequency (f clk_i/o ). alternatively, one of four taps from the prescaler can be used as a clock source. the prescaled clock has a frequency of either f clk_i/o /8, f clk_i/o /64, f clk_i/o /256, or f clk_i/o /1024. prescaler reset the prescaler is free running, i.e., operates independently of the clock select logic of the timer/counter, and it is shared by timer/counter1 and timer/counter0. since the prescaler is not affected by the timer/counter? s clock select, the state of t he prescaler will have implications for situations where a prescaled clock is used. one example of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (6 > csn2:0 > 1). the number of system clock cycles from when the timer is enabled to the first count occurs can be from 1 to n+1 system clock cycles, where n equals the prescaler divisor (8, 64, 256, or 1024). it is possible to use the prescaler reset for synchronizing the timer/counter to program execu- tion. however, care must be taken if the othe r timer/counter that shares the same prescaler also uses prescaling. a prescaler reset will affect the prescaler period for all timer/counters it is connected to. external clock source an external clock source applied to the t1/t0 pin can be used as timer/counter clock (clk t1 /clk t0 ). the t1/t0 pin is sampled once every syst em clock cycle by the pin synchronization logic. the synchronized (s ampled) signal is then passed through the edge detector. figure 38 shows a functional equivalent block diagram of the t1/t0 synchronization and edge detector logic. the registers are clocked at the po sitive edge of the internal system clock ( clk i/o ). the latch is transparent in the high period of the internal system clock. the edge detector generates one clk t1 /clk t 0 pulse for each positive (csn2:0 = 7) or negative (csn2:0 = 6) edge it detects. figure 38. t1/t0 pin sampling the synchronization and e dge detector logic introduces a de lay of 2.5 to 3.5 system clock cycles from an edge has been applied to the t1/t0 pin to the counter is updated. enabling and disabling of the clock input must be done when t1/t0 has been stable for at least one system clock cycle, otherwise it is a risk t hat a false timer/counter clock pulse is generated. each half period of the exter nal clock applied must be longer than one system clock cycle to ensure correct sampling. the external clock must be guaranteed to have less than half the sys- tem clock frequency (f extclk < f clk_i/o /2) given a 50/50% duty cycle. since the edge detector uses sampling, the maximum frequency of an external clock it can detect is half the sampling fre- tn_sync (to clock select logic) edge detector synchronization dq dq le dq tn clk i/o 81 2543l?avr?08/10 attiny2313 quency (nyquist sampling theorem). however, due to variation of the system clock frequency and duty cycle caused by oscillator source (crystal, resonator, and capacitors) tolerances, it is recommended that maximum frequency of an external clock source is less than f clk_i/o /2.5. an external clock source can not be prescaled. figure 39. prescaler for timer/counter0 and timer/counter1 (1) note: 1. the synchronization logic on the input pins ( t1/t0) is shown in figure 38 . general timer/counter control register ? gtccr ? bits 7..1 ? res: reserved bits these bits are reserved bits in the attiny2313 and will a lways read as zero. ? bit 0 ? psr10: prescaler reset timer/counter1 and timer/counter0 when this bit is one, timer/co unter1 and timer/counter 0 prescaler will be reset. this bit is nor- mally cleared immediately by hardware. note that timer/counter1 and timer/counter0 share the same prescaler and a reset of th is prescaler will affect both timers. psr10 clear clk t1 clk t0 t1 t0 clk i/o synchronization synchronization bit 7 6 5 4 3 2 1 0 ? ? ? ? ? ? ? psr10 gtccr read/write r r r r r r r r/w initial value 0 0 0 0 0 0 0 0 82 2543l?avr?08/10 attiny2313 16-bit timer/counter1 the 16-bit timer/counter unit allows accurate program execution timing (event management), wave generation, and signal timing measurement. the main features are: ? true 16-bit design (i.e., allows 16-bit pwm) ? two independent output compare units ? double buffered output compare registers ? one input capture unit ? input capture noise canceler ? clear timer on compare match (auto reload) ? glitch-free, phase correct pulse width modulator (pwm) ? variable pwm period ? frequency generator ? external event counter ? four independent interrupt sources (tov1, ocf1a, ocf1b, and icf1) overview most register and bit references in this sect ion are written in general form. a lower case ?n? replaces the timer/counter number, and a lower case ?x? replaces the output compare unit channel. however, when using the register or bi t defines in a program, the precise form must be used, i.e., tcnt1 for accessing timer/counter1 counter value and so on. a simplified block diagram of the 16 -bit timer/counter is shown in figure 40 . for the actual placement of i/o pins, refer to ?pinout attiny2313? on page 2 . cpu accessible i/o registers, including i/o bits and i/o pins, are shown in bold. the device-specific i/o register and bit loca- tions are listed in the ?16-bit timer/counter register description? on page 104 . figure 40. 16-bit timer/counter block diagram (1) note: 1. refer to figure 1 on page 2 for timer/counter1 pin placement and description. clock select timer/counter data b u s ocrna ocrnb icrn = = tcntn waveform generation waveform generation ocna ocnb noise canceler icpn = fixed top values edge detector control logic = 0 top bottom count clear direction tovn (int.req.) ocna (int.req.) ocnb (int.req.) icfn (int.req.) tccrna tccrnb ( from analog comparator ouput ) tn edge detector ( from prescaler ) clk tn 83 2543l?avr?08/10 attiny2313 registers the timer/counter (tcnt1), output compare registers (ocr1a/b), and input capture regis- ter (icr1) are all 16-bit registers. special proc edures must be followed when accessing the 16- bit registers. these procedures are described in the section ?accessing 16-bit registers? on page 84 . the timer/counter co ntrol registers (tccr1a/b) are 8-bit registers and have no cpu access restrictions. interrup t requests (abbreviated to int.req. in the figure) signals are all visible in the timer interrupt flag register (tifr). all interrupts are in dividually masked with the timer interrupt mask register (timsk). tifr and timsk are not shown in the figure. the timer/counter can be clocked internally, via th e prescaler, or by an external clock source on the t1 pin. the clock select logic block contro ls which clock source and edge the timer/counter uses to increment (or decrement) its value. th e timer/counter is inactive when no clock source is selected. the output from th e clock select logic is referred to as the timer clock (clk t 1 ). the double buffered output compare registers (ocr1a/b) are compared with the timer/coun- ter value at all time. the result of the compare can be used by the waveform generator to generate a pwm or variable frequency output on the output compare pin (oc1a/b). see ?out- put compare units? on page 90. . the compare match event will also set the compare match flag (ocf1a/b) which can be used to generate an output compare interrupt request. the input capture register can c apture the timer/counter value at a given external (edge trig- gered) event on either the input capture pin (icp1) or on the analog comparator pins ( see ?analog comparator? on page 149. ) the input capture unit includes a digital filtering unit (noise canceler) for reducing the chance of capturing noise spikes. the top value, or maximum timer/counter valu e, can in some modes of operation be defined by either the ocr1a register, the icr1 regist er, or by a set of fixed values. when using ocr1a as top value in a pwm mode, the ocr1a register can not be used for generating a pwm output. however, the top value will in this case be do uble buffered allowing the top value to be changed in run time. if a fixed top value is required, the icr1 register can be used as an alternative, freeing the ocr1a to be used as pwm output. definitions the following definitions are used ex tensively throughout the section: compatibility the 16-bit timer/counter has been updated and impr oved from previous versions of the 16-bit avr timer/counter. this 16-bit timer/counter is fully compatible with the earlier version regarding: ? all 16-bit timer/counter related i/o register address locations, including timer interrupt registers. ? bit locations inside all 16-bit timer/counter registers, including timer interrupt registers. ? interrupt vectors. the following control bits have changed name, but have same functionality and register location: ? pwm10 is changed to wgm10. ? pwm11 is changed to wgm11. ? ctc1 is changed to wgm12. table 42. definitions bottom the counter reaches the bottom when it becomes 0x0000. max the counter reaches its max imum when it becomes 0xffff (decimal 65535). top the counter reaches the top when it becomes equal to the highest value in the count sequence. the top value can be assigned to be one of the fixed values: 0x00ff, 0x01ff, or 0x03ff, or to the value stored in the ocr1a or icr1 regis- ter. the assignment is dependent of the mode of operation. 84 2543l?avr?08/10 attiny2313 the following bits are added to the 16-bit timer/counter control registers: ? foc1a and foc1b are added to tccr1a. ? wgm13 is added to tccr1b. the 16-bit timer/counter has improvements that will affect the compatibility in some special cases. accessing 16-bit registers the tcnt1, ocr1a/b, and icr1 are 16-bit regist ers that can be accessed by the avr cpu via the 8-bit data bus. the 16-bit register must be byte accessed using two read or write operations. each 16-bit timer has a single 8-bit register for temporary storing of the high byte of the 16-bit access. the same temporary register is shared between all 16-bit registers within each 16-bit timer. accessing the low byte triggers the 16-bit read or write operation. when the low byte of a 16-bit register is written by the cpu, the high byte stored in the temporary register, and the low byte written are both copied into the 16-bit regist er in the same clock cycle. when the low byte of a 16-bit register is read by the cpu, the high by te of the 16-bit register is copied into the tempo- rary register in the same clock cycle as the low byte is read. not all 16-bit accesses uses the temporary regi ster for the high byte. reading the ocr1a/b 16- bit registers does not involve using the temporary register. to do a 16-bit write, the high byte must be written before the low byte. for a 16-bit read, the low byte must be read before the high byte. the following code examples show how to acce ss the 16-bit timer registers assuming that no interrupts updates the temporary register. the same principle can be used directly for accessing the ocr1a/b and icr1 registers. note that when using ?c?, the compiler handles the 16-bit access. 85 2543l?avr?08/10 attiny2313 note: 1. the example code assumes that t he part specific header file is included. for i/o registers located in ex tended i/o map, ?in?, ?out?, ? sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructions that allow access to extended i/o. typically ?lds? and ?sts? combined with ?sbr s?, ?sbrc?, ?sbr?, and ?cbr?. the assembly code example returns the t cnt1 value in the r17:r16 register pair. it is important to notice that accessing 16-bit registers are atomic operations. if an interrupt occurs between the two instructions accessing the 16-bit register, and the interrupt code updates the temporary register by accessing the sa me or any other of the 16-bit timer registers, then the result of the access outside the interrupt will be corrupted. therefore, when both the main code and the interrupt code update the temporary register, the main code must disable the interrupts during the 16-bit access. assembly code examples (1) ... ; set tcnt 1 to 0x01ff ldi r17,0x01 ldi r16,0xff out tcnt 1 h,r17 out tcnt 1 l,r16 ; read tcnt 1 into r17:r16 in r16,tcnt 1 l in r17,tcnt 1 h ... c code examples (1) unsigned int i; ... /* set tcnt 1 to 0x01ff */ tcnt 1 = 0x1ff; /* read tcnt 1 into i */ i = tcnt 1 ; ... 86 2543l?avr?08/10 attiny2313 the following code examples show how to do an atomic read of the tcnt1 register contents. reading any of the ocr1a/b or icr1 register s can be done by using the same principle. note: 1. the example code assumes that t he part specific header file is included. for i/o registers located in ex tended i/o map, ?in?, ?out?, ? sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructions that allow access to extended i/o. typically ?lds? and ?sts? combined with ?sbr s?, ?sbrc?, ?sbr?, and ?cbr?. the assembly code example returns the t cnt1 value in the r17:r16 register pair. assembly code example (1) tim16_readtcnt 1 : ; save global interrupt flag in r18,sreg ; disable interrupts cli ; read tcnt 1 into r17:r16 in r16,tcnt 1 l in r17,tcnt 1 h ; restore global interrupt flag out sreg,r18 ret c code example (1) unsigned int tim16_readtcnt 1 ( void ) { unsigned char sreg; unsigned int i; /* save global interrupt flag */ sreg = sreg; /* disable interrupts */ __disable_interrupt(); /* read tcnt 1 into i */ i = tcnt 1 ; /* restore global interrupt flag */ sreg = sreg; return i; } 87 2543l?avr?08/10 attiny2313 the following code examples show how to do an at omic write of the tcnt1 register contents. writing any of the ocr1a/b or icr1 register s can be done by using the same principle. note: 1. the example code assumes that t he part specific header file is included. for i/o registers located in ex tended i/o map, ?in?, ?out?, ? sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructions that allow access to extended i/o. typically ?lds? and ?sts? combined with ?sbr s?, ?sbrc?, ?sbr?, and ?cbr?. the assembly code example requires that the r17: r16 register pair contains the value to be writ- ten to tcnt1. reusing the temporary high byte register if writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte only needs to be written once. however, note that the same rule of atomic operation described previously also applies in this case. assembly code example (1) tim16_writetcnt 1 : ; save global interrupt flag in r18,sreg ; disable interrupts cli ; set tcnt 1 to r17:r16 out tcnt 1 h,r17 out tcnt 1 l,r16 ; restore global interrupt flag out sreg,r18 ret c code example (1) void tim16_writetcnt 1 ( unsigned int i ) { unsigned char sreg; unsigned int i; /* save global interrupt flag */ sreg = sreg; /* disable interrupts */ __disable_interrupt(); /* set tcnt 1 to i */ tcnt 1 = i; /* restore global interrupt flag */ sreg = sreg; } 88 2543l?avr?08/10 attiny2313 timer/counter clock sources the timer/counter can be clocked by an internal or an external clock source. the clock source is selected by the clock select logic which is controlled by the clock select (cs12:0) bits located in the timer/counter control register b (tccr1b). for details on clock sources and prescaler, see ?timer/counter0 and timer/counter1 prescalers? on page 80 . counter unit the main part of the 16-bit timer/counter is th e programmable 16-bit bi-directional counter unit. figure 41 shows a block diagram of the counter and its surroundings. figure 41. counter unit block diagram signal description (internal signals): count increment or decrement tcnt1 by 1. direction select between increment and decrement. clear clear tcnt1 (set all bits to zero). clk t 1 timer/counter clock. top signalize that tcnt1 ha s reached maximum value. bottom signalize that tcnt1 has re ached minimum value (zero). the 16-bit counter is mapped into two 8-bit i/o memory locations: counter high (tcnt1h) con- taining the upper eight bits of the counter, and counter low (tcnt1l) containing the lower eight bits. the tcnt1h register can only be indirect ly accessed by the cpu. when the cpu does an access to the tcnt1h i/o location, the cpu accesses the high byte temporary register (temp). the temporary register is updated with the tcnt1h value when the tcnt1l is read, and tcnt1h is updated with the temporary register va lue when tcnt1l is written. this allows the cpu to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus. it is important to notice that there are special cases of writing to the tcnt1 register when the counter is counting that will gi ve unpredictable results. the s pecial cases are described in the sections where they are of importance. depending on the mode of operation used, the co unter is cleared, incremented, or decremented at each timer clock (clk t 1 ). the clk t 1 can be generated from an external or internal clock source, selected by the clock select bits (cs12:0). when no clock sour ce is selected (cs12:0 = 0) the timer is stopped. however, the tcnt1 value can be accessed by the cpu, independent of whether clk t 1 is present or not. a cpu write overrides (has priority over) all counter clear or count operations. the counting sequence is determined by the setting of the waveform generation mode bits (wgm13:0) located in the timer/counter control registers a and b (tccr1a and tccr1b). there are close connections between how the counter behaves (counts) and how waveforms are generated on the output compare outputs oc1x. for more details about advanced counting sequences and waveform generation, see ?modes of operation? on page 94 . temp (8-bit) data bus (8-bit) tcntn (16-bit counter) tcntnh (8-bit) tcntnl (8-bit) control logic count clear direction tovn (int.req.) clock select top bottom tn edge detector ( from prescaler ) clk tn 89 2543l?avr?08/10 attiny2313 the timer/counter overflow flag (tov1) is set a ccording to the mode of operation selected by the wgm13:0 bits. tov1 can be us ed for generating a cpu interrupt. input capture unit the timer/counter incorporates an input capture unit that can capture external events and give them a time-stamp indicating time of occurrence. the external signal indicating an event, or mul- tiple events, can be applied via the icp1 pin or al ternatively, via the analog-comparator unit. the time-stamps can then be used to calculate frequenc y, duty-cycle, and other features of the sig- nal applied. alternatively the time-stamps can be used for creating a log of the events. the input capture unit is illustrated by the block diagram shown in figure 42 . the elements of the block diagram that are not directly a part of the input capture unit are gray shaded. the small ?n? in register and bit names indicates the timer/counter number. figure 42. input capture unit block diagram when a change of the logic level (an event) occurs on the input capture pin (icp1), alternatively on the analog comparator output (aco), and this change confirms to the setting of the edge detector, a capture will be triggered. when a captur e is triggered, the 16-bit value of the counter (tcnt1) is written to the input capture register (icr1). the input capture flag (icf1) is set at the same system clock as the tcnt1 value is copi ed into icr1 register. if enabled (icie1 = 1), the input capture flag generates an input capt ure interrupt. the icf1 flag is automatically cleared when the interrupt is executed. alternativ ely the icf1 flag can be cleared by software by writing a logical one to its i/o bit location. reading the 16-bit value in the input capture register (icr1) is done by first reading the low byte (icr1l) and then the high byte (icr1h). when the low byte is read the high byte is copied into the high byte temporary regi ster (temp). when th e cpu reads the icr1h i/o location it will access the temp register. the icr1 register can only be written when using a waveform generation mode that utilizes the icr1 register for defining the counter?s top value. in these cases the waveform genera- tion mode (wgm13:0) bits must be set before t he top value can be written to the icr1 register. when writing the icr1 re gister the high byte must be written to the icr1h i/o location before the low byte is written to icr1l. icfn (int.req.) analog comparator write icrn (16-bit register) icrnh (8-bit) noise canceler icpn edge detector temp (8-bit) data bus (8-bit) icrnl (8-bit) tcntn (16-bit counter) tcntnh (8-bit) tcntnl (8-bit) acic* icnc ices aco* 90 2543l?avr?08/10 attiny2313 for more information on how to access the 16-bit registers refer to ?accessing 16-bit registers? on page 84 . input capture trigger source the main trigger source for the input capture unit is the input capture pin (icp1). timer/counter1 can alternatively use the analog comparator output as trigger source for the input capture unit. the analog comparator is selected as trigger source by setting the analog comparator input capture (acic) bit in the analog comparator control and status register (acsr). be aware that changing trigger source can trigger a capture. the input capture flag must therefore be cleared after the change. both the input capture pin (icp1) and the analog comparator output (aco) inputs are sampled using the same technique as for the t1 pin ( figure 38 on page 80 ). the edge detector is also identical. however, when the noise canceler is enabled, additional logic is inserted before the edge detector, which increases t he delay by four system clock cycles. note that the input of the noise canceler and edge detector is always enabl ed unless the timer/counter is set in a wave- form generation mode that uses icr1 to define top. an input capture can be trigger ed by software by controlling the port of the icp1 pin. noise canceler the noise canceler improves noise immunity by using a simple digita l filtering scheme. the noise canceler input is monitored over four samples, and all four must be equal for changing the output that in turn is used by the edge detector. the noise canceler is enabled by setting the input capture noise canceler (icnc1) bit in timer/counter control register b (tccr1b). when enabled the noise canceler introduces addi- tional four system clock cycles of delay from a change applied to the input, to the update of the icr1 register. the noise canceler uses the sy stem clock and is therefore not affected by the prescaler. using the input capture unit the main challenge when using the input capture unit is to assign enough processor capacity for handling the incoming events. the time between two events is critical. if the processor has not read the captured valu e in the icr1 register before th e next event occurs, the icr1 will be overwritten with a new value. in this case the result of the ca pture will be incorrect. when using the input capture in terrupt, the icr1 register shoul d be read as early in the inter- rupt handler routine as possible. even though the input capture interrupt has relatively high priority, the maximum interrupt response time is dependent on the maximum number of clock cycles it takes to handle any of the other interrupt requests. using the input capture unit in any mode of operation when the top value (resolution) is actively changed during operation, is not recommended. measurement of an external signal?s duty cycle requires that the trigger edge is changed after each capture. changing the edge sensing must be done as early as possible after the icr1 register has been read. after a change of the edge, the input capture flag (icf1) must be cleared by software (writing a logical one to the i/o bit location). for measuring frequency only, the clearing of the icf1 flag is not r equired (if an interrupt handler is used). output compare units the 16-bit comparator continuously compares tcnt1 with the output compare register (ocr1x). if tcnt equals ocr1x the comparator signals a match. a match will set the output compare flag (ocf1x) at the next timer clock cycle . if enabled (ocie1x = 1), the output com- pare flag generates an output compare interrup t. the ocf1x flag is automatically cleared when the interrupt is executed. al ternatively the ocf1x flag can be cleared by software by writ- ing a logical one to its i/o bit location. the waveform generator uses the match signal to generate an output according to operating mode set by the waveform generation mode (wgm13:0) bits and compare output mode (com1x1:0) bits. the top and bottom signals 91 2543l?avr?08/10 attiny2313 are used by the waveform generator for handling the special cases of the extreme values in some modes of operation ( see ?modes of operation? on page 94. ) a special feature of output comp are unit a allows it to define the timer/counter top value (i.e., counter resolution). in addition to the counter resolution, the top val ue defines the period time for waveforms generated by the waveform generator. figure 43 shows a block diagram of the output comp are unit. the small ?n? in the register and bit names indicates the device number (n = 1 for timer/counter 1), and the ?x? indicates output compare unit (a/b). the elements of the block di agram that are not directly a part of the output compare unit are gray shaded. figure 43. output compare unit, block diagram the ocr1x register is double buffered when using any of the twelve pulse width modulation (pwm) modes. for the normal and clear timer on compare (ctc) modes of operation, the double buffering is disabled. the double buff ering synchronizes the update of the ocr1x com- pare register to either top or bottom of the counting sequence. the synchronization prevents the occurrence of odd-length, non-symmetrical pwm pulses, thereby making the out- put glitch-free. the ocr1x register access may seem complex, but this is not case. when the double buffering is enabled, the cpu has access to the ocr1x buffer register, and if double buffering is dis- abled the cpu will access the ocr1x directly. the content of the ocr1x (buffer or compare) register is only changed by a write operation (the timer/counter does not update this register automatically as the tcnt1 and icr1 register). therefore ocr1x is not read via the high byte temporary register (temp). however, it is a good practice to read the low byte first as when accessing other 16-bit registers. writing the oc r1x registers must be done via the temp reg- ister since the compare of all 16 bits is done continuously. the high byte (ocr1xh) has to be written first. when the high byte i/o location is written by the cpu, the temp register will be updated by the value written. then when the low by te (ocr1xl) is written to the lower eight bits, the high byte will be copied into the upper 8-bits of either the ocr1x bu ffer or ocr1x compare register in the same system clock cycle. ocfnx (int.req.) = (16-bit comparator ) ocrnx buffer (16-bit register) ocrnxh buf. (8-bit) ocnx temp (8-bit) data bus (8-bit) ocrnxl buf. (8-bit) tcntn (16-bit counter) tcntnh (8-bit) tcntnl (8-bit) comnx1:0 wgmn3:0 ocrnx (16-bit register) ocrnxh (8-bit) ocrnxl (8-bit) waveform generator top bottom 92 2543l?avr?08/10 attiny2313 for more information of how to acce ss the 16-bit registers refer to ?accessing 16-bit registers? on page 84 . force output compare in non-pwm waveform generation modes, the match output of the comparator can be forced by writing a one to the force output compare (foc1x) bit. forcing compare match will not set the ocf1x flag or reload/clear the timer, but the oc1x pin will be updated as if a real compare match had occurred (the com11:0 bits settings define whether the oc1x pin is set, cleared or toggled). compare match blocking by tcnt1 write all cpu writes to the tcnt1 register will block any compare match that occurs in the next timer clock cycle, even when the timer is stopped. this feature allows ocr1x to be initialized to the same value as tcnt1 without triggering an inte rrupt when the timer/counter clock is enabled. using the output compare unit since writing tcnt1 in any mode of operation will block all comp are matches for one timer clock cycle, there are risks involved when changi ng tcnt1 when using any of the output compare channels, independent of whether the timer/counter is running or not. if the value written to tcnt1 equals the ocr1x value, the compare matc h will be missed, resulting in incorrect wave- form generation. do not write the tcnt1 equal to top in pwm modes with variable top values. the compare match for the top will be ignored and the counte r will continue to 0xffff. similarly, do not write the tcnt1 value equal to bottom when the counter is downcounting. the setup of the oc1x should be performed before setting the data direction register for the port pin to output. the easiest way of setting the oc1x value is to use the force output com- pare (foc1x) strobe bits in normal mode. the oc1x register keeps its value even when changing between waveform generation modes. be aware that the com1x1:0 bits are not doubl e buffered together with the compare value. changing the com1x1:0 bits will take effect immediately. 93 2543l?avr?08/10 attiny2313 compare match output unit the compare output mode (com1x1:0) bits have two func tions. the waveform generator uses the com1x1:0 bits for defining the output co mpare (oc1x) state at the next compare match. secondly the com1x1:0 bits control the oc1x pin output source. figure 44 shows a simplified schematic of the logic affected by the com1x1:0 bit setting. the i/o registers, i/o bits, and i/o pins in the figure are shown in bold. only the parts of the general i/o port control registers (ddr and port) that are affected by the com1x1:0 bits are shown. when referring to the oc1x state, the reference is for the internal oc1x re gister, not the oc1x pin. if a system reset occur, the oc1x register is reset to ?0?. figure 44. compare match output unit, schematic the general i/o port function is overridden by the output compare (oc1x) from the waveform generator if either of the com1x1:0 bits are se t. however, the oc1x pin direction (input or out- put) is still controlled by the data direction register (ddr) for the port pin. the data direction register bit for the oc1x pin (ddr_oc1x) must be set as output before th e oc1x value is visi- ble on the pin. the port overri de function is generally indep endent of the waveform generation mode, but there are some exceptions. refer to table 43 , table 44 and table 45 for details. the design of the output compare pin logic allows initialization of the oc 1x state before the out- put is enabled. note that some com1x1:0 bi t settings are reserved for certain modes of operation. see ?16-bit timer/counter regist er description? on page 104. the com1x1:0 bits have no effect on the input capture unit. port ddr dq dq ocnx pin ocnx dq waveform generator comnx1 comnx0 0 1 data b u s focnx clk i/o 94 2543l?avr?08/10 attiny2313 compare output mode and waveform generation the waveform generator uses the com1x1:0 bits differently in normal, ctc, and pwm modes. for all modes, setting the com1x1:0 = 0 tell s the waveform generator that no action on the oc1x register is to be performed on the next compare match. for compare output actions in the non-pwm modes refer to table 43 on page 104 . for fast pwm mode refer to table 44 on page 104 , and for phase correct and phase and frequency correct pwm refer to table 45 on page 105 . a change of the com1x1:0 bits st ate will have effect at the first compare match after the bits are written. for non-pwm modes, the action can be fo rced to have immediate effect by using the foc1x strobe bits. modes of operation the mode of operation, i.e., t he behavior of the timer/counter and the output compare pins, is defined by the combination of the waveform generation mode (wgm13:0) and compare output mode (com1x1:0) bits. the compare output mode bits do not affect the counting sequence, while the waveform generation mode bits do. the com1x1:0 bits control whether the pwm out- put generated should be inverted or not (inverted or non-inverted pwm). for non-pwm modes the com1x1:0 bits control whether the output should be set, cleared or toggle at a compare match ( see ?compare match output unit? on page 93. ) for detailed timing information refer to ?timer/counter timing diagrams? on page 102 . normal mode the simplest mode of operation is the normal mode (wgm13:0 = 0). in this mode the counting direction is always up (incre menting), and no counter clear is performed. the counter simply overruns when it passes its maximum 16-bit value (max = 0xffff) and then restarts from the bottom (0x0000). in normal operation the timer/counter overflow flag (tov1) will be set in the same timer clock cycle as the tcnt1 beco mes zero. the tov1 flag in this case behaves like a 17th bit, except that it is only set, not cleared. however, combined with the timer overflow interrupt that automatically clears the tov1 flag , the timer resolution ca n be increased by soft- ware. there are no special cases to consider in the normal mode, a new counter value can be written anytime. the input capture unit is easy to use in normal mode. however, observe that the maximum interval between the external events must not exceed the resolution of the counter. if the interval between events are too long, the timer overflow interrupt or the prescaler must be used to extend the resolution for the capture unit. the output compare units can be used to generat e interrupts at some given time. using the output compare to gene rate waveforms in norm al mode is not recommended, since this will occupy too much of the cpu time. clear timer on compare match (ctc) mode in clear timer on compare or ctc mode (wgm13:0 = 4 or 12), the ocr1a or icr1 register are used to manipulate the counter resolution. in ctc mode the counter is cleared to zero when the counter value (tcnt1) matches either the oc r1a (wgm13:0 = 4) or the icr1 (wgm13:0 = 12). the ocr1a or icr1 define the top value for the counter, hence also its resolution. this mode allows greater control of the compare match ou tput frequency. it also simplifies the opera- tion of counting external events. the timing diagram for the ctc mode is shown in figure 45 on page 95 . the counter value (tcnt1) increases until a compare match occurs with either ocr1a or icr1, and then counter (tcnt1) is cleared. 95 2543l?avr?08/10 attiny2313 figure 45. ctc mode, timing diagram an interrupt can be generated at each time the counter value reaches the top value by either using the ocf1a or icf1 flag according to the re gister used to define the top value. if the inter- rupt is enabled, the interrupt handler routine ca n be used for updating the top value. however, changing the top to a value close to bottom w hen the counter is running with none or a low prescaler value must be done with care since the ctc mode does not have the double buffering feature. if the new value written to ocr1a or icr1 is lowe r than the current value of tcnt1, the counter will miss the compare matc h. the counter will th en have to count to its maximum value (0xffff) and wrap around starting at 0x0000 before the compare match can occur. in many cases this feature is not desirable. an alternativ e will then be to use the fast pwm mode using ocr1a for defining top (wgm13:0 = 15) si nce the ocr1a then will be double buffered. for generating a waveform output in ctc mode, the ocfa output can be set to toggle its logical level on each compare match by setting the compare output mode bits to toggle mode (com1a1:0 = 1). the ocf1a value will not be visi ble on the port pin unless the data direction for the pin is set to output (ddr_ocf1a = 1). the waveform generated will have a maximum frequency of f oc 1 a = f clk_i/o /2 when ocr1a is set to zero (0x0000). the waveform frequency is defined by the following equation: the n variable represents the prescaler factor (1, 8, 64, 256, or 1024). as for the normal mode of operation, the tov1 flag is set in the same time r clock cycle that the counter counts from max to 0x0000. tcntn ocna (toggle) ocna interrupt flag set or icfn interrupt flag set (interrupt on top) 1 4 period 2 3 (comna1:0 = 1) f ocna f clk_i/o 2 n 1 ocrna + () ?? -------------------------------------------------- - = 96 2543l?avr?08/10 attiny2313 fast pwm mode the fast pulse width modulation or fast pwm mode (wgm13:0 = 5, 6, 7, 14, or 15) provides a high frequency pwm waveform generation option. the fast pwm differs from the other pwm options by its single-slope operation. the counter counts from bottom to top then restarts from bottom. in non-inverting compare output mode, the output compare (oc1x) is set on the compare match between tcnt1 and ocr1x, and cleared at top. in inverting compare output mode output is cleared on compare match and set at top. due to the single-slope oper- ation, the operating frequency of the fast pwm mo de can be twice as high as the phase correct and phase and frequency correct pwm modes that use dual-slope operation. this high fre- quency makes the fast pwm mode well suited fo r power regulation, re ctification, and dac applications. high frequency allows physically sm all sized external com ponents (coils, capaci- tors), hence reduces total system cost. the pwm resolution for fast pwm can be fixed to 8- , 9-, or 10-bit, or defined by either icr1 or ocr1a. the minimum resolution allowed is 2-bit (icr1 or ocr1a set to 0x0003), and the max- imum resolution is 16-bit (icr1 or ocr1a set to max). the pwm resolution in bits can be calculated by using the following equation: in fast pwm mode the co unter is incremented until the counter value matches either one of the fixed values 0x00ff, 0x01ff, or 0x03ff (wgm13:0 = 5, 6, or 7), the value in icr1 (wgm13:0 = 14), or the value in ocr1a (wgm13:0 = 15). th e counter is then cleared at the following timer clock cycle. the timing diagram for the fast pwm mode is shown in figure 46 . the figure shows fast pwm mode when ocr1a or icr1 is used to define top. the tcnt1 value is in the timing diagram shown as a histogram for illustrating t he single-slope operation. the diagram includes non-inverted and inverted pwm outputs. the small horizontal line marks on the tcnt1 slopes represent compare matches between ocr1x and tcnt1. the oc1x interrupt flag will be set when a compare match occurs. figure 46. fast pwm mode, timing diagram the timer/counter overflow flag (tov1) is set each time the counter reaches top. in addition the ocf1a or icf1 flag is set at the same timer clock cycle as tov1 is set when either ocr1a or icr1 is used for defining the top value. if o ne of the interrupts are enabled, the interrupt han- dler routine can be used for updating the top and compare values. when changing the top value the program must ensure that the new top value is higher or equal to the value of all of the compare registers. if the top value is lower than any of the compare registers, a compare match will never occur between the tcnt1 and the ocr1x. r fpwm top 1 + () log 2 () log ---------------------------------- - = tcntn ocrnx/top update and tovn interrupt flag set and ocna interrupt flag set or icfn interrupt flag set (interrupt on top) 1 7 period 2 3 4 5 6 8 ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) 97 2543l?avr?08/10 attiny2313 note that when using fixed top values the unused bits are masked to zero when any of the ocr1x registers are written. the procedure for updating icr1 differs from updating ocr1a when used for defining the top value. the icr1 register is not double buffered. this means that if icr1 is changed to a low value when the counter is running with none or a lo w prescaler value, there is a risk that the new icr1 value written is lower than the current va lue of tcnt1. the result will then be that the counter will miss the compare matc h at the top value. the counter will then have to count to the max value (0xffff) and wrap around starting at 0x0000 before the compare match can occur. the ocr1a register however, is double buffered. this feature allows the ocr1a i/o location to be written anytime. when the ocr1a i/o location is written the value written will be put into the ocr1a buffer register. th e ocr1a compare register will th en be updated with the value in the buffer register at the next timer clo ck cycle the tcnt1 matches top. the update is done at the same timer clock cycle as the tcnt 1 is cleared and the tov1 flag is set. using the icr1 register for defining top work s well when using fixed top values. by using icr1, the ocr1a register is free to be used for generating a pwm output on oc1a. however, if the base pwm frequency is actively change d (by changing the top value), using the ocr1a as top is clearly a better choice due to its double buffer feature. in fast pwm mode, the compare units allow generation of pwm waveforms on the oc1x pins. setting the com1x1:0 bits to two will produce a non-inverted pwm and an inverted pwm output can be generated by setting the com1x1:0 to three (see table 43 on page 104 ). the actual oc1x value will only be visible on the port pin if th e data direction for the po rt pin is set as output (ddr_oc1x). the pwm waveform is generated by setting (or clearing) the oc1x register at the compare match between ocr1x and tcnt1, and clearing (or setting) the oc1x register at the timer clock cycle the counter is cleared (changes from top to bottom). the pwm frequency for the output can be calculated by the following equation: the n variable represents the prescaler divider (1, 8, 64, 256, or 1024). the extreme values for the ocr1x register re presents special cases when generating a pwm waveform output in the fast pwm mode. if the ocr1x is set equal to bottom (0x0000) the out- put will be a narrow spike for eac h top+1 timer clock cycle. se tting the ocr1x equal to top will result in a const ant high or low output (depending on the polarity of the output set by the com1x1:0 bits.) a frequency (with 50% duty cycle) waveform out put in fast pwm mode can be achieved by set- ting ocf1a to toggle its logical level on each compare match (com1a1:0 = 1). the waveform generated will have a maximum frequency of f oc 1 a = f clk_i/o /2 when ocr1a is set to zero (0x0000). this feature is similar to the ocf1 a toggle in ctc mode, except the double buffer feature of the output compare unit is enabled in the fast pwm mode. f ocnxpwm f clk_i/o n 1 top + () ? ---------------------------------- - = 98 2543l?avr?08/10 attiny2313 phase correct pwm mode the phase correct pulse width modulation or phase correct pwm mode (wgm13:0 = 1, 2, 3, 10, or 11) provides a high resolution phase correct pwm waveform generation option. the phase correct pwm mode is, like the phase and frequency correct pwm mode, based on a dual- slope operation. the counter counts repeatedly from bottom (0x0000) to top and then from top to bottom. in non-inverting compare output mode, the output compare (oc1x) is cleared on the compare match between tcnt1 and ocr1x while upcounting, and set on the compare match while downcounting. in inverting output compare mode, the operation is inverted. the dual-slope operation has lower maximum operation frequency than single slope operation. however, due to the symmetric feat ure of the dual-slope pwm modes, these modes are preferred for motor control applications. the pwm resolution for the phase correct pwm mode can be fixed to 8-, 9-, or 10-bit, or defined by either icr1 or ocr1a. the minimum resolution allowed is 2-bit (icr1 or ocr1a set to 0x0003), and the maximum resolution is 16-bit (icr1 or ocr1a set to max). the pwm resolu- tion in bits can be calculated by using the following equation: in phase correct pwm mode the counter is incr emented until the counter value matches either one of the fixed values 0x00ff, 0x01ff, or 0x 03ff (wgm13:0 = 1, 2, or 3), the value in icr1 (wgm13:0 = 10), or the value in ocr1a (wgm13:0 = 11). the counter has then reached the top and changes the count direct ion. the tcnt1 value will be equa l to top for one timer clock cycle. the timing diagram for the ph ase correct pwm mode is shown on figure 47 . the figure shows phase correct pwm mode when ocr1a or icr1 is used to define top. the tcnt1 value is in the timing diagram shown as a histogram for illustrati ng the dual-slope operation. the diagram includes non-inverted and inverted pwm outputs. the small horizontal line marks on the tcnt1 slopes represent compare matches between ocr1x and tcnt1. the oc1x inter- rupt flag will be set when a compare match occurs. figure 47. phase correct pwm mode, timing diagram the timer/counter overflow flag (tov1) is se t each time the counter reaches bottom. when either ocr1a or icr1 is used for defining the to p value, the ocf1a or ic f1 flag is set accord- ingly at the same timer clock cycle as the ocr1x registers are updated with the double buffer r pcpwm top 1 + () log 2 () log ---------------------------------- - = ocrnx/top update and ocna interrupt flag set or icfn interrupt flag set (interrupt on top) 1 2 3 4 tovn interrupt flag set (interrupt on bottom) tcntn period ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) 99 2543l?avr?08/10 attiny2313 value (at top). the interr upt flags can be used to generate an interrupt each time the counter reaches the top or bottom value. when changing the top value the program must ensure that the new top value is higher or equal to the value of all of the compare registers. if the top value is lower than any of the compare registers, a compare match will never occur between the tcnt1 and the ocr1x. note that when using fixed top values, the unus ed bits are masked to zero when any of the ocr1x registers are written. as the third period shown in figure 47 illustrates, changing the top actively while the timer/counter is runni ng in the phase correct mode can result in an unsymmetrical output. the reason for this can be found in the time of update of the ocr1x reg- ister. since the ocr1x update occurs at top, the pwm period starts and ends at top. this implies that the length of the falling slope is determined by the previous top value, while the length of the rising slope is determined by th e new top value. when thes e two values differ the two slopes of the period will differ in length. the difference in length gives the unsymmetrical result on the output. it is recommended to use the phase and frequency correct mode instead of the phase correct mode when changing the top value while the timer/counter is running. when using a static top value there are practically no differ ences between the two modes of operation. in phase correct pwm mode, the compare units allow generation of pwm waveforms on the oc1x pins. setting the com1x1:0 bits to tw o will produce a non-inverte d pwm and an inverted pwm output can be generated by setting the com1x1:0 to three (see table 44 on page 104 ). the actual oc1x value will only be visible on the port pin if the data direction for the port pin is set as output (ddr_oc1x). the pwm waveform is generated by setting (or clearing) the oc1x register at the compare match between ocr1x and tcnt1 when the counter increments, and clearing (or setting) the oc1x register at compare match between ocr1x and tcnt1 when the counter decrements. the pw m frequency for the output when using phase correct pwm can be calculated by the following equation: the n variable represents the prescaler divider (1, 8, 64, 256, or 1024). the extreme values for the ocr1x register re present special cases when generating a pwm waveform output in the phase correct pwm mode. if the ocr1x is set equal to bottom the output will be continuously low and if set equal to top the output will be continuously high for non-inverted pwm mode. for in verted pwm the output will have the opposite logic values. f ocnxpcpwm f clk_i/o 2 ntop ?? --------------------------- - = 100 2543l?avr?08/10 attiny2313 phase and frequency correct pwm mode the phase and frequency correct pulse width modulation, or phase and frequency correct pwm mode (wgm13:0 = 8 or 9) provides a high reso lution phase and frequency correct pwm wave- form generation option. the phase and frequency correct pwm mode is, like the phase correct pwm mode, based on a dual-slope operation. the counter counts repeatedly from bottom (0x0000) to top and then from top to bottom. in non-inverting compare output mode, the output compare (oc1x) is cleared on the co mpare match between tcnt1 and ocr1x while upcounting, and set on the compare match while downcounting. in inverting compare output mode, the operation is inverted. the dual-slope operation gives a lower maximum operation fre- quency compared to the single-slope operation. howe ver, due to the symme tric feature of the dual-slope pwm modes, these modes are preferred for motor control applications. the main difference between the phase correct, and the phase and frequency correct pwm mode is the time the ocr1x register is u pdated by the ocr1x buffer register, (see figure 47 and figure 48 ). the pwm resolution for the phase and frequency correct pwm mode can be defined by either icr1 or ocr1a. the minimum resolution allowed is 2-bit (icr1 or ocr1a set to 0x0003), and the maximum resolution is 16-bit (icr1 or ocr1 a set to max). the pwm re solution in bits can be calculated using the following equation: in phase and frequency correct pwm mode the counter is incremented until the counter value matches either the value in icr1 (wgm13:0 = 8), or the value in ocr1a (wgm13:0 = 9). the counter has then reac hed the top and ch anges the count di rection. the tcnt1 value will be equal to top for one timer clock cycle. the timi ng diagram for the phase correct and frequency correct pwm mode is shown on figure 48 . the figure shows phase and frequency correct pwm mode when ocr1a or icr1 is used to define top. the tcnt1 value is in the timing diagram shown as a histogram for illustrating the dual- slope operation. the diagram incl udes non- inverted and inverted pwm outputs. the small hor izontal line marks on t he tcnt1 slopes repre- sent compare matches between oc r1x and tcnt1. the oc1x inte rrupt flag will be set when a compare match occurs. figure 48. phase and frequency correct pwm mode, timing diagram r pfcpwm top 1 + () log 2 () log ---------------------------------- - = ocrnx/top updateand tovn interrupt flag set (interrupt on bottom) ocna interrupt flag set or icfn interrupt flag set (interrupt on top) 1 2 3 4 tcntn period ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) 101 2543l?avr?08/10 attiny2313 the timer/counter overflow flag (tov1) is set at the same timer cloc k cycle as the ocr1x registers are updated with the double buffer value (at bottom). when either ocr1a or icr1 is used for defining the top value, the ocf1a or icf1 flag set when tcnt1 has reached top. the interrupt flags can then be used to generate an interrupt each time the counter reaches the top or bottom value. when changing the top value the program must ensure that the new top value is higher or equal to the value of all of the compare registers. if the top value is lower than any of the compare registers, a compare match will neve r occur between the tcnt1 and the ocr1x. as figure 48 shows the output generated is, in contra st to the phase correct mode, symmetrical in all periods. since the ocr1x registers are up dated at bottom, the length of the rising and the falling slopes will always be equal. this gives sy mmetrical output pulses and is therefore fre- quency correct. using the icr1 register for defining top work s well when using fixed top values. by using icr1, the ocr1a register is free to be used for generating a pwm output on oc1a. however, if the base pwm frequency is actively change d by changing the top value, using the ocr1a as top is clearly a better choice due to its double buffer feature. in phase and frequency correct pwm mode, the compare units allow generation of pwm wave- forms on the oc1x pins. settin g the com1x1:0 bits to two will produce a non-inverted pwm and an inverted pwm output can be generated by setting the com1x1:0 to three (see table 45 on page 105 ). the actual oc1fx value will only be visible on the port pin if th e data direction for the port pin is set as output ( ddr_ocf1x). the pwm waveform is gen erated by setting (or clearing) the ocf1x register at the compare match be tween ocr1x and tcnt1 when the counter incre- ments, and clearing (or setting) the ocf1x re gister at compare match between ocr1x and tcnt1 when the counter decrem ents. the pwm frequency for the output when using phase and frequency correct pwm can be calculated by the following equation: the n variable represents the prescaler divider (1, 8, 64, 256, or 1024). the extreme values for the ocr1x register re presents special cases when generating a pwm waveform output in the phase correct pwm mode. if the ocr1x is set equal to bottom the output will be continuously low and if set equal to top the output will be set to high for non- inverted pwm mode. for inverted pwm the ou tput will have the opposite logic values. f ocnxpfcpwm f clk_i/o 2 ntop ?? --------------------------- - = 102 2543l?avr?08/10 attiny2313 timer/counter timing diagrams the timer/counter is a synchronous design and the timer clock (clk t1 ) is therefore shown as a clock enable signal in the following figures. the figures include information on when interrupt flags are set, and when the ocr1x register is updated with the ocr1x buffer value (only for modes utilizing doub le buffering). figure 49 shows a timing diagram fo r the setting of ocf1x. figure 49. timer/counter timing diagram, setting of ocf1x, no prescaling figure 50 shows the same timing data, but with the prescaler enabled. figure 50. timer/counter timing diagram, se tting of ocf1x, with prescaler (f clk_i/o /8) figure 51 shows the count sequence close to top in various modes. when using phase and frequency correct pwm mode the ocr1x register is updated at bottom. the timing diagrams will be the same, but top should be replaced by bottom, top-1 by bottom+1 and so on. the same renaming applies for modes that set the tov1 flag at bottom. clk tn (clk i/o /1) ocfnx clk i/o ocrnx tcntn ocrnx value ocrnx - 1 ocrnx ocrnx + 1 ocrnx + 2 ocfnx ocrnx tcntn ocrnx value ocrnx - 1 ocrnx ocrnx + 1 ocrnx + 2 clk i/o clk tn (clk i/o /8) 103 2543l?avr?08/10 attiny2313 figure 51. timer/counter timing diagram, no prescaling figure 52 shows the same timing data, but with the prescaler enabled. figure 52. timer/counter timing diagram, with prescaler (f clk_i/o /8) tovn (fpwm) and icfn (if used as top) ocrnx (update at top) tcntn (ctc and fpwm) tcntn (pc and pfc pwm) top - 1 top top - 1 top - 2 old ocrnx value new ocrnx value top - 1 top bottom bottom + 1 clk tn (clk i/o /1) clk i/o tovn (fpwm) and icf n (if used as top) ocrnx (update at top) tcntn (ctc and fpwm) tcntn (pc and pfc pwm) top - 1 top top - 1 top - 2 old ocrnx value new ocrnx value top - 1 top bottom bottom + 1 clk i/o clk tn (clk i/o /8) 104 2543l?avr?08/10 attiny2313 16-bit timer/counter register description timer/counter1 control register a ? tccr1a ? bit 7:6 ? com1a1:0: compare output mode for channel a ? bit 5:4 ? com1b1:0: compare output mode for channel b the com1a1:0 and com1b1:0 control the out put compare pins (oc1a and oc1b respec- tively) behavior. if one or both of the com1a1:0 bits are written to one, the oc1a output overrides the normal port functionality of the i/o pin it is connected to. if one or both of the com1b1:0 bit are written to one, the oc1b output overrides the normal port functionality of the i/o pin it is connected to. however, note that the data direction register (ddr) bit correspond- ing to the oc1a or oc1b pin must be set in order to enable the output driver. when the oc1a or oc1b is connected to the pin, the function of the com1x1:0 bits is depen- dent of the wgm13: 0 bits setting. table 43 shows the com1x1:0 bit functionality when the wgm13:0 bits are set to a normal or a ctc mode (non-pwm). table 44 shows the com1x1:0 bit functionality when the wgm13:0 bits are set to the fast pwm mode. bit 7 6 5 4 3210 com1a1 com1a0 com1b1 com1b0 ? ? wgm11 wgm10 tccr1a read/write r/w r/w r/w r/w r r r/w r/w initial value 0 0 0 0 0 0 0 0 table 43. compare output mode, non-pwm com1a1/com1b1 com1a 0/com1b0 description 0 0 normal port operation, oc1a/oc1b disconnected. 0 1 toggle oc1a/oc1b on compare match. 1 0 clear oc1a/oc1b on compare match (set output to low level). 1 1 set oc1a/oc1b on compare match (set output to high level). table 44. compare output mode, fast pwm (1) com1a1/com1b1 com1a 0/com1b0 description 0 0 normal port operation, oc1a/oc1b disconnected. 0 1 wgm13=0: normal port operation, oc1a/oc1b disconnected. wgm13=1: toggle oc1a on compare match, oc1b reserved. 1 0 clear oc1a/oc1b on compare match, set oc1a/oc1b at top 1 1 set oc1a/oc1b on compare match, clear oc1a/oc1b at top 105 2543l?avr?08/10 attiny2313 note: 1. a special case occurs when ocr1a/ocr1b equals top and com1a1/com1b1 is set. in this case the compare match is ignored, but the set or clear is done at top. see ?fast pwm mode? on page 96. for more details. table 45 shows the com1x1:0 bit functionality when the wgm13:0 bits are set to the phase cor- rect or the phase and frequency correct, pwm mode. note: 1. a special case occurs when ocr1a/ocr1b equals top and com1a1/com1b1 is set. see ?phase correct pwm mode? on page 98. for more details. ? bit 1:0 ? wgm11:0: waveform generation mode combined with the wgm13:2 bits found in the tc cr1b register, these bits control the counting sequence of the counter, the source for maximu m (top) counter value, and what type of wave- form generation to be used, see table 46 . modes of operation suppor ted by the timer/counter unit are: normal mode (counter), clear timer on compare match (ctc) mode, and three types of pulse width modulation (pwm) modes. ( see ?modes of operation? on page 94. ). table 45. compare output mode, phase correct and phase and frequency correct pwm (1) com1a1/com1b1 com1a 0/com1b0 description 0 0 normal port operation, oc1a/oc1b disconnected. 0 1 wgm13=0: normal port operation, oc1a/oc1b disconnected. wgm13=1: toggle oc1a on compare match, oc1b reserved. 1 0 clear oc1a/oc1b on compare match when up- counting. set oc1a/oc1b on compare match when downcounting. 1 1 set oc1a/oc1b on compare match when up- counting. clear oc1a/oc1b on compare match when downcounting. 106 2543l?avr?08/10 attiny2313 note: 1. the ctc1 and pwm11:0 bit definition names are obsolete. use the wgm12:0 definitions. however, the functionality and location of these bits are compatible with previous versions of the timer. table 46. waveform generation mode bit description (1) mode wgm13 wgm12 (ctc1) wgm11 (pwm11) wgm10 (pwm10) timer/counter mode of operation top update of ocr1 x at tov1 flag set on 0 0 0 0 0 normal 0xffff immediate max 1 0 0 0 1 pwm, phase correct, 8-bit 0x00ff top bottom 2 0 0 1 0 pwm, phase correct, 9-bit 0x01ff top bottom 3 0 0 1 1 pwm, phase correct, 10-bit 0x03ff top bottom 4 0 1 0 0 ctc ocr1a immediate max 5 0 1 0 1 fast pwm, 8-bit 0x00ff top top 6 0 1 1 0 fast pwm, 9-bit 0x01ff top top 7 0 1 1 1 fast pwm, 10-bit 0x03ff top top 8 1 0 0 0 pwm, phase and frequency correct icr1 bottom bottom 9 1 0 0 1 pwm, phase and frequency correct ocr1a bottom bottom 10 1 0 1 0 pwm, phase correct icr1 top bottom 11 1 0 1 1 pwm, phase correct ocr1a top bottom 12 1 1 0 0 ctc icr1 immediate max 13 1 1 0 1 (reserved) ? ? ? 14 1 1 1 0 fast pwm icr1 top top 15 1 1 1 1 fast pwm ocr1a top top 107 2543l?avr?08/10 attiny2313 timer/counter1 control register b ? tccr1b ? bit 7 ? icnc1: input capture noise canceler setting this bit (to one) activates the input capt ure noise canceler. when the noise canceler is activated, the input from the inpu t capture pin (icp1) is filtered. the filter function requires four successive equal valued samples of the icp1 pin for changing its output. the input capture is therefore delayed by four oscillator cycles when the noise canceler is enabled. ? bit 6 ? ices1: input capture edge select this bit selects which edge on the input capture pin (icp1) that is used to trigger a capture event. when the ices1 bit is written to zero, a falling (negative) edge is used as trigger, and when the ices1 bit is written to one, a risi ng (positive) edge w ill trigger the capture. when a capture is triggered according to the ices1 setting, the counter value is copied into the input capture register (icr1). the event will also set the input capture flag (icf1), and this can be used to cause an input capture in terrupt, if this in terrupt is enabled. when the icr1 is used as top value (see description of the wgm13:0 bits located in the tccr1a and the tccr1b register), the icp1 is disconnected and consequently the input cap- ture function is disabled. ? bit 5 ? reserved bit this bit is reserved for future use. for ensuring compatibility with future de vices, this bit must be written to zero when tccr1b is written. ? bit 4:3 ? wgm13:2: waveform generation mode see tccr1a register description. ? bit 2:0 ? cs12:0: clock select the three clock select bits select the clock source to be used by the timer/counter, see figure 49 and figure 50 . if external pin modes are used for the timer/counter1, transitions on the t1 pin will clock the counter even if the pin is configured as an outpu t. this feature allows software control of the counting. bit 7654 3210 icnc1 ices1 ? wgm13 wgm12 cs12 cs11 cs10 tccr1b read/write r/w r/w r r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 table 47. clock select bit description cs12 cs11 cs10 description 0 0 0 no clock source (timer/counter stopped). 001clk i/o /1 (no prescaling) 010clk i/o /8 (from prescaler) 011clk i/o /64 (from prescaler) 100clk i/o /256 (from prescaler) 101clk i/o /1024 (from prescaler) 1 1 0 external clock source on t1 pin. clock on falling edge. 1 1 1 external clock source on t1 pin. clock on rising edge. 108 2543l?avr?08/10 attiny2313 timer/counter1 control register c ? tccr1c ? bit 7 ? foc1a: force output compare for channel a ? bit 6 ? foc1b: force output compare for channel b the foc1a/foc1b bits are only active when the wgm13:0 bits specifies a non-pwm mode. however, for ensuring compatibilit y with future devices, these bits must be set to zero when tccr1a is written when operating in a pw m mode. when writing a logical one to the foc1a/foc1b bit, an immediate compare matc h is forced on the wave form generation unit. the oc1a/oc1b output is changed according to its com1x1:0 bits setting. note that the foc1a/foc1b bits are implemented as strobes. therefore it is the value present in the com1x1:0 bits that determine t he effect of the forced compare. a foc1a/foc1b strobe will not generate any interrupt nor will it clear t he timer in clear timer on compare match (ctc) mode using ocr1a as top. the foc1a/foc1b bits are always read as zero. timer/counter1 ? tcnt1h and tcnt1l the two timer/counter i/o locations (tcnt1h and tcnt1l , combined tcnt1) give direct access, both for read and for write operations, to the timer/counter unit 16-bit counter. to ensure that both the high and low bytes are read and written simultaneously when the cpu accesses these registers, the access is perfo rmed using an 8-bit temporary high byte register (temp). this temporary register is shared by all the other 16-bit registers. see ?accessing 16-bit registers? on page 84. modifying the counter (tcnt1) while the counte r is running introduces a risk of missing a com- pare match between tcnt1 and one of the ocr1x registers. writing to the tcnt1 register blocks (removes ) the compare match on the following timer clock for all compare units. output compare register 1 a ? ocr1ah and ocr1al bit 7654 3210 foc1a foc1b ? ? ? ? ? ? tccr1c read/write w w r r r r r r initial value 0 0 0 0 0 0 0 0 bit 76543210 tcnt1[15:8] tcnt1h tcnt1[7:0] tcnt1l read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 ocr1a[15:8] ocr1ah ocr1a[7:0] ocr1al read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 109 2543l?avr?08/10 attiny2313 output compare register 1 b - ocr1bh and ocr1bl the output compare registers contain a 16-bit value that is continuo usly compared with the counter value (tcnt1). a match can be used to generate an output compare interrupt, or to generate a waveform output on the oc1x pin. the output compare registers are 16-bit in size. to ensure that both the high and low bytes are written simultaneously when the cp u writes to these registers, the access is performed using an 8-bit temporary high byte register (temp). this te mporary register is shared by all the other 16- bit registers. see ?accessing 16-bit registers? on page 84. input capture register 1 ? icr1h and icr1l the input capture is updated with the counter (tcnt1) value each time an event occurs on the icp1 pin (or optionally on the analog comparator output for timer/counter1). the input capture can be used for defining the counter top value. the input capture register is 16-bit in size. to ensure that both the high and low bytes are read simultaneously when the cpu accesses these regi sters, the access is performed using an 8-bit temporary high byte register (temp). this temporary register is shared by all the other 16-bit registers. see ?accessing 16-bit registers? on page 84. timer/counter interrupt mask register ? timsk ? bit 7 ? toie1: timer/counter1, overflow interrupt enable when this bit is written to one, and the i-flag in the status register is set (interrupts globally enabled), the timer/counter1 overflow interrupt is enabled. the corresponding interrupt vector ( see ?interrupts? on page 44. ) is executed when the tov1 flag, located in tifr, is set. ? bit 6 ? ocie1a: timer/counter1, output compare a match interrupt enable when this bit is written to one, and the i-flag in the status register is set (interrupts globally enabled), the timer/counter1 output compare a match interrupt is enabled. the corresponding interrupt vector ( see ?interrupts? on page 44. ) is executed when the ocf1a flag, located in tifr, is set. ? bit 5 ? ocie1b: timer/counter1, output compare b match interrupt enable when this bit is written to one, and the i-flag in the status register is set (interrupts globally enabled), the timer/counter1 output compare b match interrupt is enabled. the corresponding interrupt vector ( see ?interrupts? on page 44. ) is executed when the ocf1b flag, located in tifr, is set. ? bit 3 ? icie1: timer/counter1, input capture interrupt enable bit 76543210 ocr1b[15:8] ocr1bh ocr1b[7:0] ocr1bl read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 icr1[15:8] icr1h icr1[7:0] icr1l read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 7 6 5 4 3 2 1 0 toie1 ocie1a ocie1b ?icie1 ocie0b toie0 ocie0a timsk read/write r/w r/w r/w r r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 110 2543l?avr?08/10 attiny2313 when this bit is written to one, and the i-flag in the status register is set (interrupts globally enabled), the timer/counter1 input capture interrupt is enabled. the corresponding interrupt vector ( see ?interrupts? on page 44. ) is executed when the icf1 flag, located in tifr, is set. timer/counter interrupt flag register ? tifr ? bit 7 ? tov1: timer/counter1, overflow flag the setting of this flag is dependent of the wg m13:0 bits setting. in normal and ctc modes, the tov1 flag is set when the timer overflows. refer to table 46 on page 106 for the tov1 flag behavior when using another wgm13:0 bit setting. tov1 is automatically cleared when the timer/c ounter1 overflow interrupt vector is executed. alternatively, tov1 can be cleared by writing a logic one to its bit location. ? bit 6 ? ocf1a: timer/counter1, output compare a match flag this flag is set in the timer clock cycle afte r the counter (tcnt1) va lue matches the output compare register a (ocr1a). note that a forced output compare (foc 1a) strobe will not set the ocf1a flag. ocf1a is automatically cleared when the outp ut compare match a interrupt vector is exe- cuted. alternatively, ocf1a can be cleared by writing a logic one to its bit location. ? bit 5 ? ocf1b: timer/counter1, output compare b match flag this flag is set in the timer clock cycle afte r the counter (tcnt1) va lue matches the output compare register b (ocr1b). note that a forced output compare (foc 1b) strobe will not set the ocf1b flag. ocf1b is automatically cleared when the outp ut compare match b interrupt vector is exe- cuted. alternatively, ocf1b can be cleared by writing a logic one to its bit location. ? bit 3 ? icf1: timer/count er1, input capture flag this flag is set when a capture event occurs on the icp1 pin. when th e input capture register (icr1) is set by the wgm13:0 to be used as the to p value, the icf1 flag is set when the coun- ter reaches the top value. icf1 is automatically cleared when the input capt ure interrupt vector is executed. alternatively, icf1 can be cleared by writing a logic one to its bit location. bit 76543210 tov1 ocf1a ocf1b ? icf1 ocf0b tov0 ocf0a tifr read/write r/w r/w r/w r r/w r/w r/w r/w initial value00000000 111 2543l?avr?08/10 attiny2313 usart the universal synchronous and asynchronous serial receiver and transmitter (usart) is a highly flexible serial communicati on device. the main features are: ? full duplex operation (independent serial receive and transmit registers) ? asynchronous or synchronous operation ? master or slave clocked synchronous operation ? high resolution baud rate generator ? supports serial frames with 5, 6, 7, 8, or 9 data bits and 1 or 2 stop bits ? odd or even parity generation and parity check supported by hardware ? data overrun detection ? framing error detection ? noise filtering includes false start bi t detection and digital low pass filter ? three separate interrupts on tx complete, tx data register empty and rx complete ? multi-processor communication mode ? double speed asynchronous communication mode overview a simplified block diagram of the usart transmitter is shown in figure 53 . cpu accessible i/o registers and i/o pins are shown in bold. figure 53. usart block diagram (1) note: 1. refer to figure 1 on page 2 , table 29 on page 57 , and table 26 on page 55 for usart pin placement. parity generator ubrr[h:l] udr (transmit) ucsra ucsrb ucsrc baud rate generator transmit shift register receive shift register rxd txd pin control udr (receive) pin control xck data recovery clock recovery pin control tx control rx control parity checker data bus osc sync logic clock generator transmitter receiver 112 2543l?avr?08/10 attiny2313 the dashed boxes in the block diagram separate the three main parts of the usart (listed from the top): clock generator, transmitter and receiv er. control registers are shared by all units. the clock generation logic consis ts of synchronization logic fo r external clock input used by synchronous slave operation, and the baud rate generator. the xck (transfer clock) pin is only used by synchronous transfer mode. the transmitter consists of a single write buffer, a serial shift register, parity generator and control logic for handling different serial frame formats. the write buffer allows a continuous transfer of data without any delay between frames. the receiver is the most complex part of the usart module due to its clock and data recovery units. the recovery units are used for asynchronous data reception. in addition to the recovery units, the receiver includes a parity checker, control logic, a shift register and a two level receive buffer (udr). the receiver supports the same frame formats as the transmitter, and can detect frame error, data overrun and parity errors. avr usart vs. avr uart ? compatibility the usart is fully compatible with the avr uart regarding: ? bit locations inside all usart registers. ? baud rate generation. ? transmitter operation. ? transmit buffer functionality. ? receiver operation. however, the receive buffering has two improvements that will a ffect the compat ibility in some special cases: ? a second buffer register has been added. the two buffer registers op erate as a circular fifo buffer. therefore the udr must only be read once for each incoming data! more important is the fact that the error flags (fe and dor) and the ninth data bit (rxb8) are buffered with the data in the receive buffer. t herefore the status bits must always be read before the udr register is read . otherwise the error status will be lost since the buffer state is lost. ? the receiver shift register can now act as a third buffer level. this is done by allowing the received data to remain in the serial shift register (see figure 53 ) if the buffer registers are full, until a new start bit is detected. the usar t is therefore more resistant to data overrun (dor) error conditions. the following control bits have changed name, but have same functionality and register location: ? chr9 is changed to ucsz2. ? or is changed to dor. clock generation the clock generation logic generates the base clock for the transmitter and receiver. the usart supports four modes of clock operati on: normal asynchronous, double speed asyn- chronous, master synchronous and slave sy nchronous mode. the umsel bit in usart control and status register c (ucsrc) sele cts between asynchronous and synchronous oper- ation. double speed (asynchronous mode only) is controlled by the u2x found in the ucsra register. when using synchronous mode (umsel = 1), the data direction register for the xck pin (ddr_xck) controls whether the clock source is internal (master mode) or external (slave mode). the xck pin is only active when using synchronous mode. figure 54 shows a block diagram of the clock generation logic. 113 2543l?avr?08/10 attiny2313 figure 54. clock generation logic, block diagram signal description: txclk transmitter clock (internal signal). rxclk receiver base clock (internal signal). xcki input from xck pin (internal signal). used for synchronou s slave operation. xcko clock output to xck pin (internal si gnal). used for synchronous master operation. fosc xtal pin frequency (system clock). internal clock generation ? the baud rate generator internal clock generation is used for the as ynchronous and the synchronous master modes of operation. the description in this section refers to figure 54 . the usart baud rate register (ubrr) and the down-counter connected to it function as a programmable prescaler or baud rate generator. the down-counter, running at system clock (f osc ), is loaded with the ubrr value each time the counter has counted down to zero or when the ubrrl register is written. a clock is gener ated each time the counter reaches zero. this clock is the baud rate ge nerator clock output (= f osc /(ubrr+1)). the transmitter divides the baud rate generator clock output by 2, 8 or 16 depending on mode. the baud rate generator out- put is used directly by the rece iver?s clock and data recovery un its. however, the recovery units use a state machine that uses 2, 8 or 16 stat es depending on mode set by the state of the umsel, u2x and ddr_xck bits. table 48 contains equations for calculating the baud ra te (in bits per second) and for calculating the ubrr value for each mode of operation using an internally generated clock source. note: 1. the baud rate is defined to be the transfer rate in bit per second (bps) prescaling down-counter /2 ubrr /4 /2 fosc ubrr+1 sync register osc xck pin txclk u2x umsel ddr_xck 0 1 0 1 xcki xcko ddr_xck rxcl k 0 1 1 0 edge detector ucpol table 48. equations for calculating b aud rate register setting operating mode equation for calculating baud rate (1) equation for calculating ubrr value asynchronous normal mode (u2x = 0) asynchronous double speed mode (u2x = 1) synchronous master mode baud f osc 16 ubrr 1 + () -------------------------------------- - = ubrr f osc 16 baud ----------------------- - 1 ? = baud f osc 8 ubrr 1 + () ----------------------------------- = ubrr f osc 8 baud -------------------- 1 ? = baud f osc 2 ubrr 1 + () ----------------------------------- = ubrr f osc 2 baud -------------------- 1 ? = 114 2543l?avr?08/10 attiny2313 baud baud rate (in bits per second, bps) f osc system oscillator clock frequency ubrr contents of the ubrrh and ubrrl registers, (0-4095) some examples of ubrr values for some system clock frequencies are found in table 56 (see page 134 ). double speed operation (u2x) the transfer rate can be doubled by setting the u2x bit in ucsra. setting this bit only has effect for the asynchronous operation. set this bi t to zero when using synchronous operation. setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively doubling the transfer rate for asynchronous communication. note however that the receiver will in this case only use half the number of samples (reduced from 16 to 8) for data sampling and clock recovery, and therefore a more accurate baud ra te setting and system clock are required when this mode is used. for the transmitter, there are no downsides. external clock external clocking is used by the synchronous sl ave modes of operation. the description in this section refers to figure 54 for details. external clock input from the xck pin is sampled by a synchronization register to minimize the chance of meta-stability. the output from the synchronizati on register must then pass through an edge detector before it can be used by the transmitter and receiver. this process intro- duces a two cpu clock period delay and theref ore the maximum extern al xck clock frequency is limited by the following equation: note that f osc depends on the stability of the system clock source. it is therefore recommended to add some margin to avoid possible loss of data due to frequency variations. synchronous clock operation when synchronous mode is used (umsel = 1), the xck pin will be used as either clock input (slave) or clock output (master). the depen dency between the clock edges and data sampling or data change is the same. the basic principle is that data input (on rxd) is sampled at the opposite xck clock edge of the edge the data output (txd) is changed. figure 55. synchronous mode xck timing. the ucpol bit ucrsc selects which xck clock edge is used for data sampling and which is used for data change. as figure 55 shows, when ucpol is zero the data will be changed at ris- f xck f osc 4 ----------- < rxd / txd xck rxd / txd xck ucpol = 0 ucpol = 1 sample sample 115 2543l?avr?08/10 attiny2313 ing xck edge and sampled at falling xck edge. if ucpol is set, the data will be changed at falling xck edge and sampl ed at rising xck edge. frame formats a serial frame is defined to be one character of da ta bits with synchronizat ion bits (start and stop bits), and optionally a pa rity bit for error checking. the u sart accepts all 30 combinations of the following as valid frame formats: ? 1 start bit ? 5, 6, 7, 8, or 9 data bits ? no, even or odd parity bit ? 1 or 2 stop bits a frame starts with the start bit followed by the le ast significant data bit. then the next data bits, up to a total of nine, are succeeding, ending with t he most significant bit. if enabled, the parity bit is inserted after the data bits, before the stop bits . when a complete frame is transmitted, it can be directly followed by a new frame, or the communication line can be set to an idle (high) state. figure 56 illustrates the possible comb inations of the frame formats . bits inside brackets are optional. figure 56. frame formats st start bit, always low. (n) data bits (0 to 8). p parity bit. can be odd or even. sp stop bit, always high. idle no transfers on the communication line (rxd or txd). an idle line must be high. the frame format used by the usart is set by the ucsz2:0, upm1:0 and usbs bits in ucsrb and ucsrc. the receiver and transmitter use the same setting. note that changing the setting of any of these bits will corrup t all ongoing communicati on for both the rece iver and transmitter. the usart character size (ucsz2:0) bits select the number of data bits in the frame. the usart parity mode (upm1:0) bits enable and se t the type of parity bit. the selection between one or two stop bits is done by the usart stop bit select (usbs) bit. the receiver ignores the second stop bit. an fe (frame error) will therefor e only be detected in the cases where the first stop bit is zero. parity bit calculation the parity bit is calculated by do ing an exclusive-or of all the data bits. if odd parity is used, the result of the exclusive or is inverted. the re lation between the parity bit and data bits is as follows: p even parity bit using even parity p odd parity bit using odd parity 1 0 2 3 4 [5] [6] [7] [8] [p] st sp1 [sp2] (st / idle) (idle) frame p even d n 1 ? d 3 d 2 d 1 d 0 0 p odd d n 1 ? d 3 d 2 d 1 d 0 1 = = 116 2543l?avr?08/10 attiny2313 d n data bit n of the character if used, the parity bit is locate d between the last data bit and first stop bit of a serial frame. usart initialization the usart has to be initialized before any communi cation can take place. the initialization pro- cess normally consists of setting the baud rate, setting frame format and enabling the transmitter or the receiver depending on the usag e. for interrupt driven usart operation, the global interrupt flag should be cleared (and interrupts globally disabled) when doing the initialization. before doing a re-initialization with changed baud rate or frame format, be sure that there are no ongoing transmissions during the period the regist ers are changed. the txc flag can be used to check that the transmitter has completed all transfers, and t he rxc flag can be used to check that there are no unread data in the receive buffer. note that the txc flag must be cleared before each transmission (before udr is wr itten) if it is used for this purpose. the following simple usart initialization code examples show one assembly and one c func- tion that are equal in functionality. the exampl es assume asynchronous operation using polling (no interrupts enabled) and a fixed frame format. the baud rate is given as a function parameter. for the assembly code, the baud rate parameter is assumed to be stored in the r17:r16 registers. note: 1. the example code assumes that t he part specific header file is included. for i/o registers located in ex tended i/o map, ?in?, ?out?, ? sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructions that allow access to extended i/o. typically ?lds? and ?sts? combined with ?sbr s?, ?sbrc?, ?sbr?, and ?cbr?. assembly code example (1) usart_init: ; set baud rate out ubrrh, r17 out ubrrl, r16 ; enable receiver and transmitter ldi r16, (1< 118 2543l?avr?08/10 attiny2313 data transmission ? the usart transmitter the usart transmitter is enabled by setting the transmit enable (txen) bit in the ucsrb register. when the transmitter is enabled, the no rmal port operation of the txd pin is overrid- den by the usart and given the function as t he transmitter?s serial output. the baud rate, mode of operation and frame format must be set up once before doing any transmissions. if syn- chronous operation is used, the clock on the xck pin will be overridden and used as transmission clock. sending frames with 5 to 8 data bit a data transmission is initiated by loading the tr ansmit buffer with the data to be transmitted. the cpu can load the transmit buffer by writing to the udr i/o location. the buffered data in the transmit buffer will be moved to the shift register wh en the shift register is ready to send a new frame. the shift register is loaded with new data if it is in idle state (no ongoing transmission) or immediately after the last stop bit of the previous frame is transmitted. wh en the shift register is loaded with new data, it will transf er one complete frame at the ra te given by the baud register, u2x bit or by xck depending on mode of operation. the following code examples show a simple usart transmit function based on polling of the data register empty (udre) flag. when using frames with le ss than eight bits, the most signifi- cant bits written to the udr are ignored. the u sart has to be initialized before the function can be used. for the assembly code, the data to be sent is assumed to be stored in register r16 note: 1. the example code assumes that t he part specific header file is included. for i/o registers located in ex tended i/o map, ?in?, ?out?, ? sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructions that allow access to extended i/o. typically ?lds? and ?sts? combined with ?sbr s?, ?sbrc?, ?sbr?, and ?cbr?. the function simply waits for the transmit buffer to be empty by checking the udre flag, before loading it with new data to be tr ansmitted. if the data register empty interrupt is utilized, the interrupt routine writes t he data into the buffer. assembly code example (1) usart_transmit: ; wait for empty transmit buffer sbis ucsra,udre rjmp usart_transmit ; put data (r16) into buffer, sends the data out udr,r16 ret c code example (1) void usart_transmit( unsigned char data ) { /* wait for empty transmit buffer */ while ( !( ucsra & (1< 121 2543l?avr?08/10 attiny2313 data reception ? the usart receiver the usart receiver is enabled by writing the receive enable (rxen) bit in the ucsrb regis- ter to one. when the receiver is enabled, the normal pin operation of the rxd pin is overridden by the usart and given the function as the re ceiver?s serial input. the baud rate, mode of operation and frame format must be set up once before any serial reception can be done. if syn- chronous operation is used, the clock on the xck pin will be used as transfer clock. receiving frames with 5 to 8 data bits the receiver starts data reception when it detects a valid start bit. each bit that follows the start bit will be sampled at the ba ud rate or xck clock, and shifted into the receive shift register until the first stop bit of a frame is received. a seco nd stop bit will be ignored by the receiver. when the first stop bit is received, i.e., a complete seri al frame is present in the receive shift register, the contents of the sh ift register will be moved into the receive buffer. the receive buffer can then be read by reading the udr i/o location. the following code example shows a simple us art receive function based on polling of the receive complete (rxc) flag. when using frames with less than eight bi ts the most significant bits of the data read from t he udr will be masked to zero. t he usart has to be initialized before the function can be used. note: 1. the example code assumes that the part specific header file is included. for i/o registers located in ex tended i/o map, ?in?, ?out?, ? sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructions that allow access to extended i/o. typically ?lds? and ?sts? combined with ?sbr s?, ?sbrc?, ?sbr?, and ?cbr?. the function simply waits for data to be present in the receive buffer by checking the rxc flag, before reading the buffer and returning the value. assembly code example (1) usart_receive: ; wait for data to be received sbis ucsra, rxc rjmp usart_receive ; get and return received data from buffer in r16, udr ret c code example (1) unsigned char usart_receive( void ) { /* wait for data to be received */ while ( !(ucsra & (1< 123 2543l?avr?08/10 attiny2313 note: 1. the example code assumes that the part specific header file is included. for i/o registers located in ex tended i/o map, ?in?, ?out?, ? sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructions that allow access to extended i/o. typically ?lds? and ?sts? combined with ?sbr s?, ?sbrc?, ?sbr?, and ?cbr?. the receive function example reads all the i/o r egisters into the register file before any com- putation is done. this gives an optimal receive buffer utilization since the buffer location read will be free to accept new data as early as possible. receive compete flag and interrupt the usart receiver has one flag th at indicates the receiver state. the receive complete (rxc) flag indicates if there are unread data present in the receive buf- fer. this flag is one when unread data exist in the receive buffer, and zero when the receive buffer is empty (i.e., does not contain any unread data). if the re ceiver is disabled (rxen = 0), the receive buffer will be flushed and consequently the rxc bit will become zero. when the receive complete inte rrupt enable (rxcie) in ucsrb is set, the usart receive complete interrupt will be executed as long as the rxc flag is set (provided that global inter- rupts are enabled). when interrupt-driven data reception is used, the receive complete routine must read the received data fr om udr in order to clear the rx c flag, otherwise a new interrupt will occur once the interr upt routine terminates. receiver error flags the usart receiver has three error flags: fr ame error (fe), data overrun (dor) and parity error (upe). all can be accessed by reading ucsra. common for the error flags is that they are located in the receive buffer together with the fr ame for which they indica te the error status. due to the buffering of the error flags, the ucsr a must be read before the receive buffer (udr), since reading the udr i/o location changes the buffer read location. another equality for the error flags is that they can not be altered by so ftware doing a write to th e flag location. however, all flags must be set to zero when the ucsra is written for upward compatibility of future usart implementations. none of the error flags can generate interrupts. the frame error (fe) flag indicates the state of the first stop bit of the next readable frame stored in the receive buffer. the fe flag is zero when the stop bit was correctly read (as one), and the fe flag will be one when the stop bit wa s incorrect (zero). this flag can be used for detecting out-of-sync c onditions, detecting break conditions and protocol handling. the fe flag is not affected by the setting of the usbs bit in ucsrc since the re ceiver ignores all, except for the first, stop bits. for co mpatibility with future device s, always set this bit to zero when writing to ucsra. the data overrun (dor) flag indicates data loss due to a receiver buffer full condition. a data overrun occurs when the receive buf fer is full (two characters), it is a new character waiting in the receive shift register, and a new start bit is detected. if the dor flag is set there was one or more serial frame lost between the frame last read from udr, and the next frame read from udr. for compatibility with future devices, always write this bit to zero when writing to ucsra. the dor flag is cleared when the frame received was successfully moved from the shift regis- ter to the receive buffer. the parity error (upe) flag indicates that the ne xt frame in the receive buffer had a parity error when received. if parity check is not enabled the upe bit w ill always be read zero. for compati- bility with future devices, always set this bi t to zero when wr iting to ucsra. fo r more details see ?parity bit calculation? on page 115 and ?parity checker? on page 124 . 124 2543l?avr?08/10 attiny2313 parity checker the parity checker is active when the high usar t parity mode (upm1) bit is set. type of parity check to be performed (odd or even) is selected by the upm0 bit. when enabled, the parity checker calculates the parity of the data bits in incoming frames and compares the result with the parity bit from the serial frame. the result of the check is stored in the receive buffer together with the received data and stop bits. the parity error (upe) flag can then be read by software to check if the frame had a parity error. the upe bit is set if the next character that can be read from the receive buffer had a parity error when received and the parity checking was enabled at that point (upm1 = 1). this bit is valid until the receive buffer (udr) is read. disabling the receiver in contrast to the transmitter, disabling of the receiver will be immediate. data from ongoing receptions will therefore be lost. when disabled (i.e ., the rxen is set to zero) the receiver will no longer override the normal function of the rxd port pin. the receiver buffer fifo will be flushed when the receiver is disabled. remaining data in the buffer will be lost flushing the receive buffer the receiver buffer fifo will be fl ushed when the receiver is disa bled, i.e., the buffer will be emptied of its contents. unread data will be los t. if the buffer has to be flushed during normal operation, due to for instance an error condition , read the udr i/o location until the rxc flag is cleared. the following code example shows how to flush the receive buffer. note: 1. the example code assumes that the part specific header file is included. for i/o registers located in ex tended i/o map, ?in?, ?out?, ? sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructions that allow access to extended i/o. typically ?lds? and ?sts? combined with ?sbr s?, ?sbrc?, ?sbr?, and ?cbr?. asynchronous data reception the usart includes a clock recovery and a data recovery unit for handling asynchronous data reception. the clock recovery l ogic is used for synchronizing the internally generated baud rate clock to the incoming asynchronous serial frames at the rxd pin. the data recovery logic sam- ples and low pass filters each incoming bit, ther eby improving the noise immunity of the receiver. the asynchronous reception operational range depends on the accuracy of the inter- nal baud rate clock, the rate of the incoming frames, and the frame size in number of bits. assembly code example (1) usart_flush: sbis ucsra, rxc ret in r16, udr rjmp usart_flush c code example (1) void usart_flush( void ) { unsigned char dummy; while ( ucsra & (1< 126 2543l?avr?08/10 attiny2313 figure 59. stop bit sampling and ne xt start bit sampling the same majority voting is done to the stop bit as done for the other bits in the frame. if the stop bit is registered to have a logic 0 valu e, the frame error (f e) flag will be set. a new high to low transition indicating the start bit of a new frame can come right after the last of the bits used for majority vo ting. for normal speed mode, the first low level sample can be at point marked (a) in figure 59 . for double speed mode the first low level must be delayed to (b). (c) marks a stop bit of full length. the early star t bit detection influences the operational range of the receiver. asynchronous operational range the operational range of the receiver is dependent on the mismatch between the received bit rate and the internally generated baud rate. if the transmitter is sending frames at too fast or too slow bit rates, or the internally generated baud rate of the receiver does not have a similar (see table 49 ) base frequency, the receiver will not be able to synchronize the fram es to the start bit. the following equations can be used to calculate the ratio of the incoming data rate and internal receiver baud rate. d sum of character size and parity size (d = 5 to 10 bit) s samples per bit. s = 16 for normal speed mode and s = 8 for double speed mode. s f first sample number used for majority voting. s f = 8 for normal speed and s f = 4 for double speed mode. s m middle sample number used for majority voting. s m = 9 for normal speed and s m = 5 for double speed mode. r slow is the ratio of the slowest incoming data ra te that can be accepted in relation to the receiver baud rate. r fast is the ratio of the fastest incoming data rate that can be accepted in relation to the receiver baud rate. table 49 and table 50 list the maximum receiver baud rate error that can be tolerated. note that normal speed mode has higher toleration of baud rate variations. 1234567 8 9 10 0/1 0/1 0/1 stop 1 123 4 5 6 0/1 rxd sample (u2x = 0) sample (u2x = 1) (a) (b) (c) table 49. recommended maximum receiver baud rate error for normal speed mode (u2x = 0) d # (data+parity bit) r slow (%) r fast (%) max total error (%) recommended max receiver error (%) 5 93.20 106.67 +6.67/-6.8 3.0 6 94.12 105.79 +5.79/-5.88 2.5 7 94.81 105.11 +5.11/-5.19 2.0 r slow d 1 + () s s 1 ? ds ? s f ++ ------------------------------------------ - = r fast d 2 + () s d 1 + () ss m + ----------------------------------- = 127 2543l?avr?08/10 attiny2313 the recommendations of the maximum receiver baud rate error was made under the assump- tion that the receiver and transmitter equally divides the maximum total error. there are two possible sources fo r the receivers baud rate erro r. the receiver?s system clock (xtal) will always have some minor instabilit y over the supply voltage range and the tempera- ture range. when using a crystal to generate the system clock, this is rarely a problem, but for a resonator the system clock may differ more than 2% depending of the resonators tolerance. the second source for the error is more controllable. the baud rate generator can not always do an exact division of the system frequen cy to get the baud rate wanted. in this case an ubrr value that gives an acceptable low error can be used if possible. 8 95.36 104.58 +4.58/-4.54 2.0 9 95.81 104.14 +4.14/-4.19 1.5 10 96.17 103.78 +3.78/-3.83 1.5 table 50. recommended maximum receiver baud rate error for double speed mode (u2x = 1) d # (data+parity bit) r slow (%) r fast (%) max total error (%) recommended max receiver error (%) 5 94.12 105.66 +5.66/-5.88 2.5 6 94.92 104.92 +4.92/-5.08 2.0 7 95.52 104,35 +4.35/-4.48 1.5 8 96.00 103.90 +3.90/-4.00 1.5 9 96.39 103.53 +3.53/-3.61 1.5 10 96.70 103.23 +3.23/-3.30 1.0 table 49. recommended maximum receiver baud rate error for normal speed mode (u2x = 0) d # (data+parity bit) r slow (%) r fast (%) max total error (%) recommended max receiver error (%) 128 2543l?avr?08/10 attiny2313 multi-processor communication mode setting the multi-processor communication mode (mpcm) bit in ucsra enables a filtering function of incoming frames received by the usart receiver. frames that do not contain address information will be ignored and not put into the receive buffer. this effectively reduces the number of incoming frames that has to be handled by the cpu, in a system with multiple mcus that communicate via the same serial bus. the transmitter is unaffected by the mpcm setting, but has to be used differently when it is a part of a system utilizing the multi-processor communication mode. if the receiver is set up to receive frames that c ontain 5 to 8 data bits, then the first stop bit indi- cates if the frame contains data or address information. if the receiver is set up for frames with nine data bits, then the ninth bit (rxb8) is used for identifying address and data frames. when the frame type bit (the first stop or the ninth bit) is one, the frame contains an address. when the frame type bit is zero the frame is a data frame. the multi-processor communication mode enables several slave mcus to receive data from a master mcu. this is done by first decoding an address frame to find out which mcu has been addressed. if a particular slave mcu has been addressed, it will receive the following data frames as normal, while the other slave mcus will ignore the received frames until another address frame is received. using mpcm for an mcu to act as a master mcu, it can use a 9-bit character frame format (ucsz = 7). the ninth bit (txb8) must be set when an address frame (txb8 = 1) or cleared when a data frame (txb = 0) is being transmitted. the slave mcus must in this case be set to use a 9-bit character frame format. the following procedure should be used to exchange data in multi-processor communication mode: 1. all slave mcus are in multi-processor co mmunication mode (mpcm in ucsra is set). 2. the master mcu sends an address frame, and all slaves receive and read this frame. in the slave mcus, the rxc flag in ucsra will be set as normal. 3. each slave mcu reads the udr register and determines if it has been selected. if so, it clears the mpcm bit in ucsra, otherwise it waits for the next address byte and keeps the mpcm setting. 4. the addressed mcu will receive all data fram es until a new addres s frame is received. the other slave mcus, which still have the mpcm bit set, will ignore the data frames. 5. when the last data frame is received by the addressed mcu, the addressed mcu sets the mpcm bit and waits for a new address frame from master. the process then repeats from 2. using any of the 5- to 8-bit character frame formats is possible, but impractical since the receiver must change between using n and n+ 1 character frame formats. this makes full- duplex operation difficult since t he transmitter and receiver uses the same character size set- ting. if 5- to 8-bit character frames are used, the transmitter must be set to use two stop bit (usbs = 1) since the first stop bit is used for indicating the frame type. do not use read-modify-write instructions (sbi and cbi) to set or clear the mpcm bit. the mpcm bit shares the same i/o location as the txc flag and this might accidentally be cleared when using sbi or cbi instructions. 129 2543l?avr?08/10 attiny2313 usart register description usart i/o data register ? udr the usart transmit data buffer register and usart receive data buffer registers share the same i/o address referred to as usart data register or udr. the transmit data buffer reg- ister (txb) will be the destination for data wri tten to the udr register location. reading the udr register location will return the contents of the receive data bu ffer register (rxb). for 5-, 6-, or 7-bi t characters the upper unus ed bits will be ignored by the transmitter and set to zero by the receiver. the transmit buffer can only be written when the udre flag in the ucsra register is set. data written to udr when the udre flag is not set, will be ignored by the usart transmitter. when data is written to the tr ansmit buffer, and the transmitter is enabled, the transm itter will load the data into the transmit sh ift register when the shift register is empty. then the data will be seri- ally transmitted on the txd pin. the receive buffer consists of a two level fifo . the fifo will change its state whenever the receive buffer is accessed. due to this behavior of the receive buffer, do not use read-modify- write instructions (sbi and cbi) on this locati on. be careful when using bit test instructions (sbic and sbis), since these also will change the state of the fifo. usart control and status register a ? ucsra ? bit 7 ? rxc: usart receive complete this flag bit is set when there are unread data in the receive buffer and cleared when the receive buffer is empty (i.e., does not contain any unread dat a). if the receiver is disabled, the receive buffer will be flushed and consequently the rx c bit will become zero. the rxc flag can be used to generate a receive complete interrup t (see description of the rxcie bit). ? bit 6 ? txc: usart transmit complete this flag bit is set when the en tire frame in the transmit shift register has been shifted out and there are no new data currently present in the transm it buffer (udr). the txc flag bit is auto- matically cleared when a transmit complete interrupt is executed, or it can be cleared by writing a one to its bit location. the txc flag can generate a transmit complete interrupt (see descrip- tion of the txcie bit). bit 76543210 rxb[7:0] udr (read) txb[7:0] udr (write) read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 rxc txc udre fe dor upe u2x mpcm ucsra read/write r r/w r r r r r/w r/w initial value00100000 130 2543l?avr?08/10 attiny2313 ? bit 5 ? udre: usart data register empty the udre flag indicates if the transmit buffer (u dr) is ready to receive new data. if udre is one, the buffer is empty, and therefore ready to be written. the udre flag can generate a data register empty interrupt (see description of the udrie bit). udre is set after a reset to indicate that the transmitter is ready. ? bit 4 ? fe: frame error this bit is set if the next character in the receive buffer had a frame error when received. i.e., when the first stop bit of the next character in th e receive buffer is zero. this bit is valid until the receive buffer (udr) is read. the fe bit is zero when the stop bit of received da ta is one. always set this bit to zero when writing to ucsra. ? bit 3 ? dor: data overrun this bit is set if a data overrun condition is detected. a data overrun occurs when the receive buffer is full (two characters), it is a new char acter waiting in the receive shift register, and a new start bit is detected. this bit is valid until the receive buffer (u dr) is read. always set this bit to zero when writing to ucsra. ? bit 2 ? upe: usart parity error this bit is set if the next character in the receive buffer had a parity error when received and the parity checking was enabled at that point (upm1 = 1). this bit is valid until the receive buffer (udr) is read. always set this bit to zero when writing to ucsra. ? bit 1 ? u2x: double the usart transmission speed this bit only has effect for the asynchronous operation. write this bit to zero when using syn- chronous operation. writing this bit to one will reduce the divisor of th e baud rate divider from 16 to 8 effectively dou- bling the transfer rate for asynchronous communication. ? bit 0 ? mpcm: multi-processor communication mode this bit enables the multi-processor communication mode. when the mpcm bit is written to one, all the incoming frames received by the usart receiver that do not contain address infor- mation will be ignored. the transmi tter is unaffected by the mpcm setting. for more detailed information see ?multi-processor communication mode? on page 128 . 131 2543l?avr?08/10 attiny2313 usart control and status register b ? ucsrb ? bit 7 ? rxcie: rx complete interrupt enable writing this bit to one enables interrupt on the rxc flag. a usart receive complete interrupt will be generated only if the rxcie bi t is written to one, the global interrupt flag in sreg is writ- ten to one and the rxc bit in ucsra is set. ? bit 6 ? txcie: tx complete interrupt enable writing this bit to one enables interrupt on t he txc flag. a usart tran smit complete interrupt will be generated only if the txcie bit is written to one, the glo bal interrupt flag in sreg is writ- ten to one and the txc bit in ucsra is set. ? bit 5 ? udrie: usart data register empty interrupt enable writing this bit to one enables interrupt on the udre flag. a data register empty interrupt will be generated only if the udrie bit is written to one, the glob al interrupt flag in sreg is written to one and the udre bit in ucsra is set. ? bit 4 ? rxen: receiver enable writing this bit to one enables the usart receiv er. the receiver will override normal port oper- ation for the rxd pin when enabled. disabling the receiver will flush the receive buffer invalidating the fe, dor, and upe flags. ? bit 3 ? txen: transmitter enable writing this bit to one enable s the usart transmitter. the tr ansmitter will override normal port operation for the txd pin when enabled. the disab ling of the transmitter (writing txen to zero) will not become effective until ongo ing and pending transmissions ar e completed, i. e., when the transmit shift register and transmit buffer register do not contain data to be transmitted. when disabled, the transmitter will no longer override the txd port. ? bit 2 ? ucsz2: character size the ucsz2 bits combined with the ucsz1:0 bit in ucsrc sets the number of data bits (char- acter size) in a frame the receiver and transmitter use. ? bit 1 ? rxb8: receive data bit 8 rxb8 is the ninth data bit of the received charac ter when operating with serial frames with nine data bits. must be read before reading the low bits from udr. ? bit 0 ? txb8: transmit data bit 8 txb8 is the ninth data bit in the character to be transmitted when operating with serial frames with nine data bits. must be writte n before writing the low bits to udr. bit 76543210 rxcie txcie udrie rxen txen ucsz2 rxb8 txb8 ucsrb read/write r/w r/w r/w r/w r/w r/w r r/w initial value00000000 132 2543l?avr?08/10 attiny2313 usart control and status register c ? ucsrc ? bit 6 ? umsel: usart mode select this bit selects between asynchronous and synchronous mode of operation. ? bit 5:4 ? upm1:0: parity mode these bits enable and set type of parity generati on and check. if enabled, the transmitter will automatically generate and send t he parity of the transmitted data bits within each frame. the receiver will generate a parity va lue for the incoming data and co mpare it to th e upm0 setting. if a mismatch is detected, the upe flag in ucsra will be set. ? bit 3 ? usbs: stop bit select this bit selects the number of stop bits to be in serted by the transmitter. the receiver ignores this setting. ? bit 2:1 ? ucsz1:0: character size the ucsz1:0 bits combined with the ucsz2 bit in ucsrb sets the number of data bits (char- acter size) in a frame the receiver and transmitter use. see table 54 on page 133 . bit 76543210 ? umsel upm1 upm0 usbs ucsz1 ucsz0 ucpol ucsrc read/write r r/w r/w r/w r/w r/w r/w r/w initial value00000110 table 51. umsel bit settings umsel mode 0 asynchronous operation 1 synchronous operation table 52. upm bits settings upm1 upm0 parity mode 0 0 disabled 01reserved 1 0 enabled, even parity 1 1 enabled, odd parity table 53. usbs bit settings usbs stop bit(s) 01-bit 12-bit 133 2543l?avr?08/10 attiny2313 ? bit 0 ? ucpol: clock polarity this bit is used for synchronous mode only. write this bit to zero when asynchronous mode is used. the ucpol bit sets the relationship betw een data output change and data input sample, and the synchronous clock (xck). usart baud rate registers ? ubrrl and ubrrh ? bit 15:12 ? reserved bits these bits are reserved for future use. for com patibility with future devi ces, these bit must be written to zero when ubrrh is written. ? bit 11:0 ? ubrr11:0: usart baud rate register this is a 12-bit register which contains the usart baud rate. the ubrrh contains the four most significant bits, and the ubrrl contains th e eight least significant bits of the usart baud rate. ongoing transmissions by the transmitter and receiver will be corrupted if th e baud rate is changed. writing ubrrl will tr igger an immediate update of the baud rate prescaler. table 54. ucsz bits settings ucsz2 ucsz1 ucsz0 character size 0005-bit 0016-bit 0107-bit 0118-bit 100reserved 101reserved 110reserved 1119-bit table 55. ucpol bit settings ucpol transmitted data changed (output of txd pin) received data sampled (input on rxd pin) 0 rising xck edge falling xck edge 1 falling xck edge rising xck edge bit 151413121110 9 8 ? ? ? ? ubrr[11:8] ubrrh ubrr[7:0] ubrrl 76543210 read/write r r r r r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 00000000 134 2543l?avr?08/10 attiny2313 examples of baud rate setting for standard crystal and resonator frequencies, the most commonly used baud rates for asyn- chronous operation can be generated by using the ubrr settings in table 56 . ubrr values which yield an actual baud rate differing less than 0.5% from the target baud rate, are bold in the table. higher error ratings are acceptable, but the receiver will have less noise resistance when the error ratings are high, especially for large serial frames (see ?asynchronous operational range? on page 126 ). the error values are calculated using the following equation: error[%] baudrate closest match baudrate -------------------------------------------------------- 1 ? ?? ?? 100% ? = table 56. examples of ubrr settings for commonly used osc illator frequencies baud rate (bps) f osc = 1.0000 mhz f osc = 1.8432 mhz f osc = 2.0000 mhz u2x = 0 u2x = 1 u2x = 0 u2x = 1 u2x = 0 u2x = 1 ubrr error ubrr error ubrr error ubrr error ubrr error ubrr error 2400 25 0.2% 51 0.2% 47 0.0% 95 0.0% 51 0.2% 103 0.2% 4800 12 0.2% 25 0.2% 23 0.0% 47 0.0% 25 0.2% 51 0.2% 9600 6 -7.0% 12 0.2% 11 0.0% 23 0.0% 12 0.2% 25 0.2% 14.4k 3 8.5% 8 -3.5% 7 0.0% 15 0.0% 8 -3.5% 16 2.1% 19.2k 2 8.5% 6 -7.0% 5 0.0% 11 0.0% 6 -7.0% 12 0.2% 28.8k 1 8.5% 3 8.5% 3 0.0% 7 0.0% 3 8.5% 8 -3.5% 38.4k 1 -18.6% 2 8.5% 2 0.0% 5 0.0% 2 8.5% 6 -7.0% 57.6k 0 8.5% 1 8.5% 1 0.0% 3 0.0% 1 8.5% 3 8.5% 76.8k ? ? 1 -18.6% 1 -25.0% 2 0.0% 1 -18.6% 2 8.5% 115.2k ? ? 0 8.5% 0 0.0% 1 0.0% 0 8.5% 1 8.5% 230.4k??????00.0%???? 250k??????????00.0% max. (1) 62.5 kbps 125 kbps 115.2 kbps 230.4 kbps 125 kbps 250 kbps 1. ubrr = 0, error = 0.0% 135 2543l?avr?08/10 attiny2313 table 57. examples of ubrr settings for commonl y used oscillator fr equencies (continued) baud rate (bps) f osc = 3.6864 mhz f osc = 4.0000 mhz f osc = 7.3728 mhz u2x = 0u2x = 1u2x = 0u2x = 1u2x = 0u2x = 1 ubrr error ubrr error ubrr error ubrr error ubrr error ubrr error 2400 95 0.0% 191 0.0% 103 0.2% 207 0.2% 191 0.0% 383 0.0% 4800 47 0.0% 95 0.0% 51 0.2% 103 0.2% 95 0.0% 191 0.0% 9600 23 0.0% 47 0.0% 25 0.2% 51 0.2% 47 0.0% 95 0.0% 14.4k 15 0.0% 31 0.0% 16 2.1% 34 -0.8% 31 0.0% 63 0.0% 19.2k 11 0.0% 23 0.0% 12 0. 2% 25 0.2% 23 0.0% 47 0.0% 28.8k 7 0.0% 15 0.0% 8 -3.5% 16 2.1% 15 0.0% 31 0.0% 38.4k 5 0.0% 11 0.0% 6 -7.0% 12 0.2% 11 0.0% 23 0.0% 57.6k 3 0.0% 7 0.0% 3 8.5% 8 -3.5% 7 0.0% 15 0.0% 76.8k 2 0.0% 5 0.0% 2 8.5% 6 -7.0% 5 0.0% 11 0.0% 115.2k 1 0.0% 3 0.0% 1 8.5% 3 8.5% 3 0.0% 7 0.0% 230.4k 0 0.0% 1 0.0% 0 8.5% 1 8.5% 1 0.0% 3 0.0% 250k 0 -7.8% 1 -7.8% 0 0.0% 1 0.0% 1 -7.8% 3 -7.8% 0.5m ? ? 0 -7.8% ? ? 0 0.0% 0 -7.8% 1 -7.8% 1m ??????????0-7.8% max. (1) 230.4 kbps 460.8 kbps 250 kbps 0.5 mbps 460.8 kbps 921.6 kbps 1. ubrr = 0, error = 0.0% 136 2543l?avr?08/10 attiny2313 table 58. examples of ubrr settings for commonl y used oscillator fr equencies (continued) baud rate (bps) f osc = 8.0000 mhz f osc = 11.0592 mhz f osc = 14.7456 mhz u2x = 0 u2x = 1 u2x = 0 u2x = 1 u2x = 0 u2x = 1 ubrr error ubrr error ubrr error ubrr error ubrr error ubrr error 2400 207 0.2% 416 -0.1% 287 0.0% 575 0.0% 383 0.0% 767 0.0% 4800 103 0.2% 207 0.2% 143 0.0% 287 0.0% 191 0.0% 383 0.0% 9600 51 0.2% 103 0.2% 71 0.0% 143 0.0% 95 0.0% 191 0.0% 14.4k 34 -0.8% 68 0.6% 47 0.0% 95 0.0% 63 0.0% 127 0.0% 19.2k 25 0.2% 51 0.2% 35 0. 0% 71 0.0% 47 0.0% 95 0.0% 28.8k 16 2.1% 34 -0.8% 23 0.0% 47 0.0% 31 0.0% 63 0.0% 38.4k 12 0.2% 25 0.2% 17 0. 0% 35 0.0% 23 0.0% 47 0.0% 57.6k 8 -3.5% 16 2.1% 11 0. 0% 23 0.0% 15 0.0% 31 0.0% 76.8k 6 -7.0% 12 0.2% 8 0.0% 17 0.0% 11 0.0% 23 0.0% 115.2k 3 8.5% 8 -3.5% 5 0.0% 11 0.0% 7 0.0% 15 0.0% 230.4k 1 8.5% 3 8.5% 2 0.0% 5 0.0% 3 0.0% 7 0.0% 250k 1 0.0% 3 0.0% 2 -7.8% 5 -7.8% 3 -7.8% 6 5.3% 0.5m 0 0.0% 1 0.0% ? ? 2 -7.8% 1 -7.8% 3 -7.8% 1m ? ? 0 0.0% ? ? ? ? 0 -7.8% 1 -7.8% max. (1) 0.5 mbps 1 mbps 691.2 kbps 1.3824 mbps 921.6 kbps 1.8432 mbps 1. ubrr = 0, error = 0.0% 137 2543l?avr?08/10 attiny2313 table 59. examples of ubrr settings for commonly used oscillator frequencies (continued) baud rate (bps) f osc = 16.0000 mhz u2x = 0 u2x = 1 ubrr error ubrr error 2400 416 -0.1% 832 0.0% 4800 207 0.2% 416 -0.1% 9600 103 0.2% 207 0.2% 14.4k 68 0.6% 138 -0.1% 19.2k 51 0.2% 103 0.2% 28.8k 34 -0.8% 68 0.6% 38.4k 25 0.2% 51 0.2% 57.6k 16 2.1% 34 -0.8% 76.8k 12 0.2% 25 0.2% 115.2k 8 -3.5% 16 2.1% 230.4k 3 8.5% 8 -3.5% 250k 3 0.0% 7 0.0% 0.5m 1 0.0% 3 0.0% 1m 0 0.0% 1 0.0% max. (1) 1. ubrr = 0, error = 0.0% 1 mbps 2 mbps 138 2543l?avr?08/10 attiny2313 universal serial interface ? usi the universal serial interface, or usi, provides the basic hardware resources needed for serial communication. combined with a minimum of cont rol software, the usi allows significantly higher transfer rates and uses less code space t han solutions based on software only. interrupts are included to minimize the processor load. the main features of the usi are: ? two-wire synchronous data transfer (master or slave, f sclmax = f ck /16) ? three-wire synchronous data transfer (master, f sckmax = f ck /2, slave f sckmax = f ck /4) ? data received interrupt ? wake-up from idle mode ? in two-wire mode: wake-up from all sl eep modes, including power-down mode ? two-wire start condition detector with interrupt capability overview a simplified block diagram of t he usi is shown on figure 60. fo r the actual placement of i/o pins, refer to ?pinout attiny2313? on page 2 . cpu accessible i/o registers, including i/o bits and i/o pins, are shown in bold. the device-specific i/o register and bit locations are listed in the ?usi register descriptions? on page 144 . figure 60. universal serial interface, block diagram the 8-bit shift register is directly accessible via the data bus and contains the incoming and outgoing data. the register has no buffering so the data must be read as quickly as possible to ensure that no data is lost. the most signific ant bit is connected to one of two output pins depending of the wire mode configuration. a trans parent latch is inserted between the serial reg- ister output and output pin, which delays the cha nge of data output to the opposite clock edge of the data input sampling. the serial input is alwa ys sampled from the data input (di) pin indepen- dent of the configuration. the 4-bit counter can be both read and writt en via the data bus, and can generate an overflow interrupt. both the serial register and the counte r are clocked simultaneously by the same clock source. this allows the counter to count the numb er of bits received or transmitted and generate an interrupt when the transfer is complete. note that when an external clock source is selected the counter counts both clock edges. in this case the c ounter counts the number of edges, and not the number of bits. the clock can be select ed from three different sources: the usck pin, timer0 overflow, or from software. data bus usipf usitc usiclk usics0 usics1 usioif usioie usidc usisif usiwm0 usiwm1 usisie bit7 two-wire clock control unit do (output only) di/sda (input/open drain) usck/scl (input/open drain) 4-bit counter usidr usisr dq le usicr clock hold tim0 ovf bit0 [1] 3 0 1 2 3 0 1 2 0 1 2 139 2543l?avr?08/10 attiny2313 the two-wire clock control unit can generate an interrupt when a start condition is detected on the two-wire bus. it can also gener ate wait states by holding the clock pin low after a start con- dition is detected, or after the counter overflows. functional descriptions three-wire mode the usi three-wire mode is compliant to the serial peripheral interface (spi) mode 0 and 1, but does not have the slave select (ss) pin functionality. however, this feature can be implemented in software if necessary. pin names used by this mode are: di, do, and usck. figure 61. three-wire mode operation, simplified diagram figure 61 shows two usi units operating in three-wir e mode, one as master and one as slave. the two shift registers are interconnected in such way that after eight usck clocks, the data in each register are interchanged. the same cloc k also increments the usi?s 4-bit counter. the counter overflow (interrupt) flag, or usioif, can therefore be used to determine when a trans- fer is completed. the clock is generated by the master device software by toggling the usck pin via the port register or by writin g a one to the usitc bit in usicr. figure 62. three-wire mode, timing diagram slave master bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 do di usck bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 do di usck portxn msb msb 654321lsb 1 2 3 4 5 6 7 8 654321lsb usck usck do di d c b a e cycle ( reference ) 140 2543l?avr?08/10 attiny2313 the three-wire mode timing is shown in figure 62 . at the top of the figure is a usck cycle refer- ence. one bit is shifted into the usi shift regi ster (usidr) for each of these cycles. the usck timing is shown for both external clock modes. in external clock mode 0 (usics0 = 0), di is sampled at positive edges, and do is changed (data register is shifted by one) at negative edges. external clock mode 1 (usics0 = 1) uses the opposite edges versus mode 0, i.e., sam- ples data at negative and changes the output at positive edges. the usi clock modes corresponds to the spi data mode 0 and 1. referring to the timing diagram (figure 62.), a bus transfer involves the following steps: 1. the slave device and master device sets up its data output and, depending on the proto- col used, enables its output driver (mark a and b). the output is set up by writing the data to be transmitted to the serial data re gister. enabling of the output is done by set- ting the corresponding bit in the port data direction register. note that point a and b does not have any specific order, but both mu st be at least one half usck cycle before point c where the data is sampled. this must be done to ensure that the data setup requirement is satisfied. the 4-bit counter is reset to zero. 2. the master generates a clock pulse by soft ware toggling the usck line twice (c and d). the bit value on the slave and master?s data input (di) pin is sampled by the usi on the first edge (c), and the data output is chan ged on the opposite edge (d). the 4-bit counter will count both edges. 3. step 2. is repeated eight times fo r a complete register (byte) transfer. 4. after eight clock pulses (i.e., 16 clock edg es) the counter will overfl ow and indicate that the transfer is completed. the data bytes transferred must now be processed before a new transfer can be initiated. the overflow interrupt will wake up the processor if it is set to idle mode. depending of the protocol us ed the slave device can now set its output to high impedance. spi master operation example the following code demonstrates how to use the usi module as a spi master: spitransfer: out usidr,r16 ldi r16,(1< 143 2543l?avr?08/10 attiny2313 figure 64. two-wire mode, typical timing diagram referring to the timing diagram (figure 64.), a bus transfer involves the following steps: 1. the a start condition is generated by the ma ster by forcing the sda low line while the scl line is high (a). sda can be forced low eith er by writing a zero to bit 7 of the shift register, or by setting the corresponding bit in the port register to zero. note that the data direction register bit must be set to one for the output to be enabled. the slave device?s start detector logic (figure 65.) det ects the start condition and sets the usisif flag. the flag can generate an interrupt if necessary. 2. in addition, the start detector will hold the scl line low after the master has forced an negative edge on this line (b). this allows the slave to wake up from sleep or complete its other tasks before setting up the shift register to receive the address. this is done by clearing the start condition flag and reset the counter. 3. the master set the first bit to be transfer red and releases the scl line (c). the slave samples the data and shift it in to the serial register at the positive edge of the scl clock. 4. after eight bits are transferred containing slave address and data direction (read or write), the slave counter overflows and the scl line is forced low (d). if the slave is not the one the master has addressed, it releases the scl line and waits for a new start condition. 5. if the slave is addressed it holds the sda line low during the acknowledgment cycle before holding the scl line low again (i.e., the counter register must be set to 14 before releasing scl at (d)). depending of the r/w bi t the master or slave enables its output. if the bit is set, a master read operation is in progress (i.e., the slave drives the sda line) the slave can hold the scl line low after the acknowledge (e). 6. multiple bytes can now be tran smitted, all in same direction, until a stop condition is given by the master (f). or a new start condition is given. if the slave is not able to receive more data it does not acknowledge the data byte it has last received. when the master does a read operation it must terminate the operation by force the acknowledge bit low after th e last byte transmitted. figure 65. start condition detector, logic diagram p s address 1 - 7 8 9 r/w ack ack 1 - 8 9 data ack 1 - 8 9 data sda scl a b d e c f sda scl write( usisif) clock hold usisif dq clr dq clr 144 2543l?avr?08/10 attiny2313 start condition detector the start condition detector is shown in figure 65. the sda line is delayed (in the range of 50 to 300 ns) to ensure valid sampling of the scl line. the start condition detector is working asynchronously and can therefore wake up the processor from the power-down sleep mode. however, the protocol used might have restrictions on the scl hold time. therefore, when us ing this feature in this case th e oscillator start-up time set by the cksel fuses (see ?clock systems and their distribution? on page 22 ) must also be taken into the consideration. alternative usi usage when the usi unit is not used for serial communi cation, it can be set up to do alternative tasks due to its flexible design. half-duplex asynchronous data transfer by utilizing the shift register in three-wire m ode, it is possible to implement a more compact and higher performance uart than by software only. 4-bit counter the 4-bit counter can be used as a stand-alone counter with overflow interrupt. note that if the counter is clocked externally, both clock edges will generate an increment. 12-bit ti mer/counter combining the usi 4-bit counter and timer/count er0 allows them to be used as a 12-bit counter. edge triggered external interrupt by setting the counter to maximum value (f) it can function as an additional external interrupt. the overflow flag and interrupt enable bit are then used for the external interrupt. this feature is selected by the usics1 bit. software interrupt the counter overflow interrupt can be used as a software interrupt trig gered by a clock strobe. usi register descriptions usi data register ? usidr the usi uses no buffering of the serial register, i.e., when accessing the data register (usidr) the serial register is accessed di rectly. if a serial clock occurs at the same cycle the register is written, the register will contain th e value written and no shift is pe rformed. a (left) shift operation is performed depending of the usics1..0 bits setting. the shift operation can be controlled by an external clock edge, by a ti mer/counter0 overflow, or direct ly by software using the usiclk strobe bit. note that even when no wire mode is selected (usiwm1..0 = 0) both the external data input (di/sda) and the external clock inpu t (usck/scl) can still be used by the shift register. the output pin in use, do or sda depending on the wire mode, is connected via the output latch to the most significant bit (bit 7) of the data register. the output latch is open (transparent) dur- ing the first half of a serial clock cycle when an external clock source is selected (usics1 = 1), and constantly open when an internal clock so urce is used (usics1 = 0). the output will be changed immediately when a new msb written as long as the latch is open. the latch ensures that data input is sampled and data ou tput is changed on opposite clock edges. note that the corresponding data direction register to the pin must be set to one for enabling data output from the shift register. bit 7 6 5 4 3 2 1 0 msb lsb usidr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 145 2543l?avr?08/10 attiny2313 usi status register ? usisr the status register contains interrupt flag s, line status flags and the counter value. ? bit 7 ? usisif: start condition interrupt flag when two-wire mode is selected, the usisif flag is set (to one) when a start condition is detected. when output disable mode or thr ee-wire mode is selected and (usicsx = 0b11 & usiclk = 0) or (usics = 0b10 & usiclk = 0), any edge on the sck pin sets the flag. an interrupt will be generated when the flag is set while th e usisie bit in usicr and the global interrupt enable flag are set. the flag will only be cleared by writing a logical one to the usisif bit. clearing this bit will release the start de tection hold of uscl in two-wire mode. a start condition interrup t will wake-up the processo r from all sleep modes. ? bit 6 ? usioif: counter overflow interrupt flag this flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to 0). an interrupt will be generate d when the flag is set while the usioie bit in usicr and the global interrupt enable flag ar e set. the flag will only be cleared if a one is written to the usioif bit. clearing this bit will release the counter overfl ow hold of scl in two-wire mode. a counter overflow interrupt will wake-up the processor from idle sleep mode. ? bit 5 ? usipf: stop condition flag when two-wire mode is selected, the usipf flag is set (one) when a stop condition is detected. the flag is cleared by writing a one to this bit. note that this is not an interrupt flag. this signal is useful when implementing two-wire bus master arbitration. ? bit 4 ? usidc: data output collision this bit is logical one when bit 7 in the shift register differs from the physical pin value. the flag is only valid when two-wire mode is used. this signal is useful when implementing two-wire bus master arbitration. ? bits 3..0 ? usicnt3..0: counter value these bits reflect the current 4-bit counter value. the 4-bit counter value can directly be read or written by the cpu. the 4-bit counter increments by one for each clock generated either by the external clock edge detector, by a timer/counter0 overflow, or by software using usiclk or usitc strobe bits. the clock source depends of the setting of the usics1 ..0 bits. for external cl ock operation a special feature is added that allows the clock to be gener ated by writing to the usitc strobe bit. this feature is enabled by write a one to the usiclk bit while setting an external clock source (usics1 = 1). note that even when no wire mode is selected (usiwm1..0 = 0) the external clock input (usck/scl) are can still be used by the counter. usi control register ? usicr the control register includes interrupt enable control, wire mode setting, clock select setting, and clock strobe. bit 76543 210 usisif usioif usipf usidc usicnt3 usicnt2 usicnt1 usicnt0 usisr read/write r/w r/w r/w r r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 bit 7 6 5 4 3 2 1 0 usisie usioie usiwm1 usiwm0 us ics1 usics0 usiclk usitc usicr read/write r/w r/w r/w r/w r/w r/w w w initial value 0 0 0 0 0 0 0 0 146 2543l?avr?08/10 attiny2313 ? bit 7 ? usisie: start condition interrupt enable setting this bit to one enables the start condition detector interrupt. if there is a pending inter- rupt when the usisie and the globa l interrupt enable flag is set to one, this will immediately be executed. ? bit 6 ? usioie: counter overflow interrupt enable setting this bit to one enables the counter overflow interrupt. if there is a pending interrupt when the usioie and the global interrupt enable flag is set to one, this will immediately be executed. ? bit 5..4 ? usiwm1..0: wire mode these bits set the type of wire mode to be us ed. basically only the f unction of the outputs are affected by these bits. data and clock inputs are not affect ed by the mode selected and will always have the same function. the counter and shift register can therefore be clocked externally, and data input sampled, even when outputs are disabled. the relations between usiwm1..0 and the usi oper ation is summarized in table 60 on page 147 . 147 2543l?avr?08/10 attiny2313 note: 1. the di and usck pins are renamed to serial data (sda) and serial clock (scl) respectively to avoid confusion between the modes of operation. table 60. relations between usiwm1..0 and the usi operation usiwm1 usiwm0 description 0 0 outputs, clock hold, and start detecto r disabled. port pins operates as normal. 0 1 three-wire mode. uses do, di, and usck pins. the data output (do) pin overrides the corresponding bit in the port register in this mode. however, the corresponding ddr bit still controls the data direction. when the port pin is set as input the pins pull-up is controlled by the port bit. the data input (di) and serial clock (usck) pins do not affect the normal port operation. when operating as master, clock pulses are software generated by toggling the port register, while the data direction is set to output. the usit c bit in the usicr register can be used for this purpose. 1 0 two-wire mode. uses sda (di) and scl (usck) pins (1) . the serial data (sda) and the serial clock (scl) pins are bi- directional and uses open-collector output drives. the output drivers are enabled by setting the corresponding bit for sda and scl in the ddr register. when the output driver is enabled fo r the sda pin, the output driver will force the line sda low if the outp ut of the shift register or the corresponding bit in the port register is zero. otherwise the sda line will not be driven (i.e., it is released). when the scl pin output driver is enabled the scl line will be forced low if the corresponding bit in the port register is zero, or by the start detector. otherwise the scl line will not be driven. the scl line is held low when a star t detector detects a start condition and the output is enabled. cleari ng the start condition flag (usisif) releases the line. the sda and scl pin inputs is not affected by enabling this mode. pull-ups on the sda and scl port pin are disabled in two-wire mode. 1 1 two-wire mode. uses sda and scl pins. same operation as for the two-wir e mode described above, except that the scl line is also held low when a counter overflow occurs, and is held low until the timer overflow flag (usioif) is cleared. 148 2543l?avr?08/10 attiny2313 ? bit 3..2 ? usics1..0: clock source select these bits set the clock source for the shift regi ster and counter. the data output latch ensures that the output is changed at th e opposite edge of the sampling of the data input (di/sda) when using external clock source (usck/scl). when so ftware strobe or timer0 overflow clock option is selected, the output latch is transparent and therefore the output is changed immediately. clearing the usics1..0 bits enables software str obe option. when using th is option, writing a one to the usiclk bit clocks both the shift r egister and the counter. for external clock source (usics1 = 1), the usiclk bit is no longer used as a strobe, but selects between external clock- ing and software clocking by the usitc strobe bit. table 61 shows the relationship between the usic s1..0 and usiclk setting and clock source used for the shift register and the 4-bit counter. ? bit 1 ? usiclk: clock strobe writing a one to this bit locati on strobes the shift register to shift one step and the counter to increment by one, provided that the usics1..0 bits are set to zero and by doing so the software clock strobe option is selected. the output will change immediately when the clock strobe is exe- cuted, i.e., in the same instruction cycle. the va lue shifted into the shift register is sampled the previous instruction cycle. the bit will be read as zero. when an external clock source is selected (usics1 = 1), the us iclk function is changed from a clock strobe to a clock select register. setting the usiclk bit in this case will select the usitc strobe bit as clock sour ce for the 4-bit counter (see table 61 ). ? bit 0 ? usitc: toggle clock port pin writing a one to this bit location t oggles the usck/scl value either from 0 to 1, or from 1 to 0. the toggling is independent of the setting in the data direction register, but if the port value is to be shown on the pin the ddb7 must be set as output (to one). this feature allows easy clock generation when implementi ng master devices. the bit will be read as zero. when an external clock source is selected (usics 1 = 1) and the usiclk bit is set to one, writ- ing to the usitc strobe bit will directly clock th e 4-bit counter. this allows an early detection of when the transfer is done when operating as a master device. table 61. relations between the usics1..0 and usiclk setting usics1 usics0 usiclk shift register clock source 4-bit counter clock source 0 0 0 no clock no clock 0 0 1 software clock strobe (usiclk) software clock strobe (usiclk) 0 1 x timer/counter0 overfl ow timer/counter0 overflow 1 0 0 external, positive edge external, both edges 1 1 0 external, negative edge external, both edges 1 0 1 external, positive ed ge software clock strobe (usitc) 1 1 1 external, negative edge software clock strobe (usitc) 149 2543l?avr?08/10 attiny2313 analog comparator the analog comparator compares the input va lues on the positive pin ain0 and negative pin ain1. when the voltage on the positive pin ain0 is higher than the voltage on the negative pin ain1, the analog comparator output, aco, is set. the comparator?s output can be set to trigger the timer/counter1 input capture function. in addition, the comparator can trigger a separate interrupt, exclusive to the analog comparator. the user can select interrupt triggering on com- parator output rise, fall or toggle. a block diagram of the comparator and its surrounding logic is shown in figure 66 . figure 66. analog comparator block diagram analog comparator control and status register ? acsr ? bit 7 ? acd: analog comparator disable when this bit is written logic one, the power to the analog comparator is switched off. this bit can be set at any time to tu rn off the analog com parator. this will reduce power consumption in active and idle mode. when changing the acd bit, the analog comparator interrupt must be disabled by clearing the acie bit in acsr. ot herwise an interrupt can occur when the bit is changed. ? bit 6 ? acbg: analog comparator bandgap select when this bit is set, a fixed bandgap reference vo ltage replaces the positive input to the analog comparator. when this bit is clea red, ain0 is applied to the positive input of the analog compar- ator. when the bandgap reference is used as input to the analog comparator, it will take a certain time for the voltage to stabilize. if not stibilized, the fi rst conversion may give a wrong value. see ?internal voltage reference? on page 38. ? bit 5 ? aco: analog comparator output the output of the analog comparator is synchron ized and then directly connected to aco. the synchronization introduces a delay of 1 - 2 clock cycles. ? bit 4 ? aci: analog comparator interrupt flag this bit is set by hardware when a comparator output event triggers t he interrupt mode defined by acis1 and acis0. the analog comparator interr upt routine is executed if the acie bit is set and the i-bit in sreg is set. aci is cleared by hardware when executing the corresponding inter- rupt handling vector. alternatively, aci is cleared by writing a logic one to the flag. ? bit 3 ? acie: analog comparator interrupt enable acbg bandgap reference bit 76543210 acd acbg aco aci acie acic acis1 acis0 acsr read/write r/w r/w r r/w r/w r/w r/w r/w initial value00n/a00000 150 2543l?avr?08/10 attiny2313 when the acie bit is written logic one and the i-bi t in the status register is set, the analog com- parator interrupt is activated. when writ ten logic zero, the interrupt is disabled. ? bit 2 ? acic: analog comparator input capture enable when written logic one, this bit enables the input ca pture function in timer/counter1 to be trig- gered by the analog comparator. the comparator outp ut is in this case directly connected to the input capture front-end logic, ma king the comparator utilize the noise canceler and edge select features of the timer/counter1 input capture interrupt. when written logic zero, no connection between the analog comparator and the input c apture function exists. to make the comparator trigger the timer/counter1 input capture interr upt, the icie1 bit in the timer interrupt mask register (timsk) must be set. ? bits 1, 0 ? acis1, acis0: analog comparator interrupt mode select these bits determine which compar ator events that trigger the an alog comparator interrupt. the different settings are shown in table 62 . when changing the acis1/acis0 bits, the analog comparator interrupt must be disabled by clearing its interrupt enable bit in the acsr re gister. otherwise an interrupt can occur when the bits are changed. digital input disable register ? didr ? bit 1, 0 ? ain1d, ain0d: ai n1, ain0 digital input disable when this bit is written logic one, the digital inpu t buffer on the ain1/0 pin is disabled. the corre- sponding pin register bit will alwa ys read as zero when this bit is set. when an analog signal is applied to the ain1/0 pin and the digital input from this pin is not needed, this bit should be writ- ten logic one to reduce power consumption in the digital input buffer. table 62. acis1/acis0 settings acis1 acis0 interrupt mode 0 0 comparator interrupt on output toggle. 01reserved 1 0 comparator interrupt on falling output edge. 1 1 comparator interrupt on rising output edge. bit 76543210 ? ? ? ? ? ? ain1d ain0d didr read/writerrrrrrr/wr/w initial value00000000 151 2543l?avr?08/10 attiny2313 debugwire on- chip debug system features ? complete program flow control ? emulates all on-chip func tions, both digital and analog, excep t reset pin ? real-time operation ? symbolic debugging support (both at c and assembler source level, or for other hlls) ? unlimited number of program break poin ts (using software break points) ? non-intrusive operation ? electrical characteristics identical to real device ? automatic configuration system ? high-speed operation ? programming of non- volatile memories overview the debugwire on-chip debug system uses a one-wire, bi-directional interface to control the program flow, execute avr instructions in t he cpu and to program the different non-volatile memories. physical interface when the debugwire enable (dwen) fuse is programmed and lock bits are unprogrammed, the debugwire system within the target device is activated. the reset port pin is configured as a wire-and (open-drain) bi-directional i/o pin with pull-up enabled and becomes the commu- nication gateway between target and emulator. figure 67. the debugwire setup figure 67 shows the schematic of a target mcu, with debugwire enabled, and the emulator connector. the system clock is not affected by debugwire and will always be the clock source selected by the cksel fuses. when designing a system where debugwire will be used, the following observations must be made for correct operation: ? pull-up resistor on the dw/(reset) line must be larger than 10k. however, the pull-up resistor is optional. d w gnd dw(reset) vcc 1.8 - 5.5 v 152 2543l?avr?08/10 attiny2313 ? connecting the reset pin directly to v cc will not work. ? capacitors inserted on th e reset pin must be disco nnected when us ing debugwire. ? all external reset source s must be disconnected. software break points debugwire supports program memory break points by the avr break instruction. setting a break point in avr studio ? will insert a break instruction in the program memo ry. the instruc- tion replaced by the break instru ction will be stored. when program execution is continued, the stored instruction will be execut ed before continuing from the program memory. a break can be inserted manually by putting the break instruction in the program. the flash must be re-programmed each time a break point is changed. this is automatically handled by avr studio th rough the debugwire inte rface. the use of brea k points will therefore reduce the flash data retention. devices used for debugging purposes should not be shipped to end customers. limitations of debugwire the debugwire communication pin (dw) is physica lly located on the same pin as external reset (reset). an external re set source is therefore not supported when the debugwire is enabled. the debugwire system accurately emulates all i/ o functions when running at full speed, i.e., when the program in the cpu is running. when the cpu is stopped, care must be taken while accessing some of the i/o registers via the de bugger (avr studio). see the debugwire docu- mentation for detailed descri ption of the limitations. a programmed dwen fuse enable s some parts of the clock system to be running in all sleep modes. this will increase the power consumption while in sleep. thus, the dwen fuse should be disabled when debugwire is not used. debugwire related register in i/o memory the following section describes the registers used with the debugwire. debugwire data register ? dwdr the dwdr register provides a communication channel from the running program in the mcu to the debugger. this register is only accessible by the debugwire and can therefore not be used as a general purpose register in the normal operations. bit 76543210 dwdr[7:0] dwdr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 153 2543l?avr?08/10 attiny2313 self- programming the flash the device provides a self-programming me chanism for downloading and uploading program code by the mcu itself. the self-programming ca n use any available data interface and associ- ated protocol to read code and write (progra m) that code into the program memory. the spm instruction is disabled by default but it ca n be enabled by programming the selfprgen fuse (to ?0?). the program memory is updated in a page by page fashion. before programming a page with the data stored in the temporary page buffer, the page must be erased. the temporary page buf- fer is filled one word at a time using spm and the buffer can be filled either before the page erase command or between a page erase and a page write operation: alternative 1, fill the bu ffer before a page erase ? fill temporary page buffer ? perform a page erase ? perform a page write alternative 2, fill the bu ffer after page erase ? perform a page erase ? fill temporary page buffer ? perform a page write if only a part of the page needs to be changed, th e rest of the page must be stored (for example in the temporary page buffer) before the erase, and then be re-written. when using alternative 1, the boot loader provides an effective read-mod ify-write feature which a llows the user software to first read the page, do the necessary changes, and then write back the modified data. if alter- native 2 is used, it is not possible to read the old data while loading since the page is already erased. the temporary page buffer can be accessed in a random sequence. it is essential that the page address used in both the page erase and page write operation is addressing the same page. performing page erase by spm to execute page erase, set up the address in the z-pointer, write ?00000011? to spmcsr and execute spm within four clock cycl es after writing spmcsr. the data in r1 and r0 is ignored. the page address must be written to pcpage in the z-register. other bits in the z-pointer will be ignored during this operation. ? the cpu is halted during the page erase operation. filling the temporary buffer (page loading) to write an instruction word, set up the addres s in the z-pointer and data in r1:r0, write ?00000001? to spmcsr and execute spm within four clock cycles after writing spmcsr. the content of pcword in the z-register is used to address the data in the temporary buffer. the temporary buffer will auto-erase after a page write operation or by writing the ctpb bit in spmcsr. it is also erased after a system reset. no te that it is not possible to write more than one time to each address without erasing the temporary buffer. if the eeprom is wr itten in the middle of an spm page load operation, all data loaded will be lost. performing a page write to execute page write, set up the address in the z-pointer, write ?00000101? to spmcsr and execute spm within four clock cycl es after writing spmcsr. the data in r1 and r0 is ignored. the page address must be written to pcpage. ot her bits in the z-point er must be written to zero during this operation. ? the cpu is halted during the page write operation. 154 2543l?avr?08/10 attiny2313 addressing the flash during self- programming the z-pointer is used to address the spm commands. since the flash is organized in pages (see table 69 on page 160 ), the program counter can be treated as having two different sect ions. one section, c onsisting of the leas t significant bits, is addressing the words within a page, while the most significant bits are addressing the pages. this is shown in figure 68 . note that the page erase and pa ge write operations are addressed independently. therefore it is of major importan ce that the software addresses the same page in both the page erase and page write operation. the lpm instruction uses the z-pointer to store the address. since this instruction addresses the flash byte-by-byte, also the lsb (bit z0) of the z-pointer is used. figure 68. addressing the flash during spm (1) note: 1. the different variables used in figure 68 are listed in table 69 on page 160 . bit 151413121110 9 8 zh (r31) z15 z14 z13 z12 z11 z10 z9 z8 zl (r30) z7z6z5z4z3z2z1z0 76543210 program memory 0 1 15 z - register bit 0 zpagemsb word address within a page page address within the flash zpcmsb instruction word pag e pcword[pagemsb:0]: 00 01 02 pageend pag e pcword pcpage pcmsb pagemsb program counter 155 2543l?avr?08/10 attiny2313 store program memory control and status register ? spmcsr the store program memory control and status regi ster contains the control bits needed to con- trol the program memory operations. ? bits 7..5 ? res: reserved bits these bits are reserved bits in the attiny2313 and always read as zero. ? bit 4 ? ctpb: clear temporary page buffer if the ctpb bit is writte n while filling the temporary page bu ffer, the temporary page buffer will be cleared and the da ta will be lost. ? bit 3 ? rflb: read fuse and lock bits an lpm instruction within th ree cycles after rflb and se lfprgen are set in the spmcsr register, will read either the lock bits or the fuse bits (depending on z0 in the z-pointer) into the destination register. see ?eeprom write prevents writi ng to spmcsr? on page 156 for details. ? bit 2 ? pgwrt: page write if this bit is written to one at the same time as selfprgen, the next sp m instruction within four clock cycles executes page write, with the data stored in the temporary buffer. the page address is taken from the high part of the z-pointer. the data in r1 and r0 are ignored. the pgwrt bit will auto-clear upon completion of a page write, or if no spm instruction is executed within four clock cycles. the cpu is halte d during the entire page write operation. ? bit 1 ? pgers: page erase if this bit is written to one at the same time as selfprgen, the next sp m instruction within four clock cycles executes page erase. the page address is taken from the high part of the z- pointer. the data in r1 and r0 are ignored. t he pgers bit will auto-clear upon completion of a page erase, or if no spm instruction is executed within four clock cycles. the cpu is halted dur- ing the entire page write operation. ? bit 0 ? selfprgen: self programming enable this bit enables the spm instruction for the next fo ur clock cycles. if written to one together with either ctpb, rflb, pgwrt, or pgers, the following spm instruction will have a special meaning, see description above. if only selfprgen is written, the follow ing spm instruction will store the value in r1:r0 in the temporary pa ge buffer addressed by the z-pointer. the lsb of the z-pointer is ignored. the selfprgen bit will auto-clear upon completion of an spm instruction, or if no spm instruction is execut ed within four clock cycles. during page erase and page write, the selfprgen bit remains high until the operation is completed. writing any other combination than ?10001?, ?01001?, ?00101?, ?00011? or ?00001? in the lower five bits will have no effect. bit 7654321 0 ? ? ? ctpb rflb pgwrt pgers selfprgen spmcsr read/write r r r r/w r/w r/w r/w r/w initial value0000000 0 156 2543l?avr?08/10 attiny2313 eeprom write prevents writing to spmcsr note that an eeprom write oper ation will block all software progra mming to flash. reading the fuses and lock bits from software will also be prevented during t he eeprom write operation. it is recommended that the user checks the status bit (eepe) in the eecr register and verifies that the bit is cleared before writing to the spmcsr register. reading the fuse and lock bits from software it is possible to read both the fuse and lock bi ts from software. to read the lock bits, load the z-pointer with 0x0001 and set the rflb and selfprgen bits in spmcsr. when an lpm instruction is executed within three cpu cycles after the rflb and selfprgen bits are set in spmcsr, the value of the lock bits will be loaded in the desti nation register . the rflb and selfprgen bits will auto-clear upon completion of reading the lock bits or if no lpm instruc- tion is executed within three cpu cycles or no spm instruction is executed within four cpu cycles. when rflb and selfprgen are cleared, lpm will work as described in the instruction set manual. the algorithm for reading the fuse low byte is similar to the one described above for reading the lock bits. to read the fuse low byte, load the z-pointer with 0x0000 and set the rflb and selfprgen bits in spmcsr. when an lpm instruct ion is executed within three cycles after the rflb and selfprgen bits are set in the spm csr, the value of the fuse low byte (flb) will be loaded in the destination re gister as shown below. refer to table 68 on page 160 for a detailed description and mapping of the fuse low byte. similarly, when reading the fuse high byte, load 0x0003 in the z-pointer. when an lpm instruc- tion is executed within three cycles after the rflb and selfprgen bits are set in the spmcsr, the value of the fuse high byte (fhb) will be loaded in the destinati on register as shown below. refer to table 67 on page 159 for detailed description and mapping of the fuse high byte. fuse and lock bits that are programmed, will be read as zero. fuse and lock bits that are unprogrammed, will be read as one. bit 76543210 rd ??????lb2lb1 bit 76543210 rd flb7 flb6 flb5 flb4 flb3 flb2 flb1 flb0 bit 76543210 rd fhb7 fhb6 fhb5 fhb4 fhb3 fhb2 fhb1 fhb0 157 2543l?avr?08/10 attiny2313 preventing flash corruption during periods of low v cc , the flash program can be corrupted because the supply voltage is too low for the cpu and the flash to operate properly. these issues are the same as for board level systems using the flash, and the same design solutions should be applied. a flash program corruption can be caused by two situ ations when the voltage is too low. first, a regular write sequence to the flash requires a minimum voltage to operate correctly. secondly, the cpu itself can execute instruct ions incorrectly, if the supply voltage for executing instructions is too low. flash corruption can easily be avoided by following these design recommendations (one is sufficient): 1. keep the avr reset active (low) during periods of insufficient power supply voltage. this can be done by enabling the internal brow n-out detector (bod) if the operating volt- age matches the detection level. if not, an external low v cc reset protection circuit can be used. if a reset occurs while a write operation is in prog ress, the write operation will be completed provided that the powe r supply voltage is sufficient. 2. keep the avr core in power-down sleep mode during periods of low v cc . this will pre- vent the cpu from attempting to decode an d execute instructions, effectively protecting the spmcsr register and thus the flash from unintentional writes. programming time for flash when using spm the calibrated rc oscillator is used to time flash accesses. table 63 shows the typical pro- gramming time for flash accesses from the cpu. table 63. spm programming time symbol min programming time max programming time flash write (page erase, page write, and write lock bits by spm) 3.7 ms 4.5 ms 158 2543l?avr?08/10 attiny2313 memory programming program and data memory lock bits the attiny2313 provides two lock bits which can be left unprogrammed (?1?) or can be pro- grammed (?0?) to obtain the additional features listed in table 65 . the lock bits can only be erased to ?1? with the chip erase command. note: 1. ?1? means unprogrammed, ?0? means programmed notes: 1. program the fuse bits and boot lock bits before programming the lb1 and lb2. 2. ?1? means unprogrammed, ?0? means programmed table 64. lock bit byte (1) lock bit byte bit no description default value 7 ? 1 (unprogrammed) 6 ? 1 (unprogrammed) 5 ? 1 (unprogrammed) 4 ? 1 (unprogrammed) 3 ? 1 (unprogrammed) 2 ? 1 (unprogrammed) lb2 1 lock bit 1 (unprogrammed) lb1 0 lock bit 1 (unprogrammed) table 65. lock bit protection modes (1)(2) memory lock bits protection type lb mode lb2 lb1 1 1 1 no memory lock features enabled. 210 further programming of the flash and eeprom is disabled in parallel and serial programming mode. the fuse bits are locked in both serial and parallel programming mode. (1) 300 further programming and verification of the flash and eeprom is disabled in para llel and serial programming mode. the boot lock bits and fuse bits are locked in both serial and parallel programming mode. (1) 159 2543l?avr?08/10 attiny2313 fuse bits the attiny2313 has three fuse bytes. table 67 and table 68 describe briefly the functionality of all the fuses and how they are map ped into the fuse byte s. note that the fuses are read as logi- cal zero, ?0?, if they are programmed. notes: 1. enables spm instruction. see ?self-programming the flash? on page 153 . note: 1. the spien fuse is not accessible in serial programming mode. 2. see ?watchdog timer control register - wdtcsr? on page 42 for details. 3. never ship a product with the dwen fuse programmed regardless of the setting of lock bits. a programmed dwen fuse enables some parts of the clock system to be running in all sleep modes. this may increase the power consumption. 4. see table 16 on page 35 for bodlevel fuse decoding. 5. see ?alternate functions of port a? on page 53 for description of rstdisbl fuse. table 66. fuse extended byte fuse extended byte bit no description default value 7 ? 1 (unprogrammed) 6 ? 1 (unprogrammed) 5 ? 1 (unprogrammed) 4 ? 1 (unprogrammed) 3 ? 1 (unprogrammed) 2 ? 1 (unprogrammed) 1 ? 1 (unprogrammed) selfprgen 0 self programming enable 1 (unprogrammed) table 67. fuse high byte fuse high byte bit no description default value dwen (3) 7 debugwire enable 1 (unprogrammed) eesave 6 eeprom memory is preserved through the chip erase 1 (unprogrammed, eeprom not preserved) spien (1) 5 enable serial program and data downloading 0 (programmed, spi prog. enabled) wdton (2) 4 watchdog timer always on 1 (unprogrammed) bodlevel2 (4) 3 brown-out detector trigger level 1 (unprogrammed) bodlevel1 (4) 2 brown-out detector trigger level 1 (unprogrammed) bodlevel0 (4) 1 brown-out detector trigger level 1 (unprogrammed) rstdisbl (5) 0 external reset disable 1 (unprogrammed) 160 2543l?avr?08/10 attiny2313 note: 1. the default value of sut1..0 results in maxi mum start-up time for th e default clock source. see table 15 on page 34 for details. 2. the default setting of cksel3..0 results in internal rc oscillator @ 8 mhz. the status of the fuse bits is not affected by chip erase. note that the fuse bits are locked if lock bit1 (lb1) is programmed. program the fuse bits before programming the lock bits. latching of fuses the fuse values are latched when the device enters programming mode and changes of the fuse values will have no effect until the part leaves programming mode. this does not apply to the eesave fuse which will take effect once it is programmed. the fuse s are also latched on power-up in normal mode. signature bytes all atmel microcontrollers have a three-byte signature code which identifies the device. this code can be read in both serial and parallel mode, also when the device is locked. the three bytes reside in a separate address space. for the attiny2313 the signature bytes are: 1. 0x000: 0x1e (indicates manufactured by atmel). 2. 0x001: 0x91 (indicates 2kb flash memory). 3. 0x002: 0x0a (indicates attiny 2313 device when 0x001 is 0x91). calibration byte signature area of attiny2313 has one byte of calibration data for the internal rc oscillator. this byte resides in the high byte of address 0x0000. during reset, this byte is automatically written into the osccal register to ensure correct frequency of the calibrated rc oscillator. see ?oscillator calibration register ? osccal? on page 26 . page size table 68. fuse low byte fuse low byte bit no description default value ckdiv8 7 divide clock by 8 0 (programmed) ckout 6 output clock on ck out pin 1 (unprogrammed) sut1 5 select start-up time 1 (unprogrammed) (1) sut0 4 select start-up time 0 (programmed) (1) cksel3 3 select clock source 0 (programmed) (2) cksel2 2 select clock source 1 (unprogrammed) (2) cksel1 1 select clock source 0 (programmed) (2) cksel0 0 select clock source 0 (programmed) (2) table 69. no. of words in a page and no. of pages in the flash flash size page size pcword no. of pages pcpage pcmsb 1k words (2k bytes) 16 words pc[3:0] 64 pc[9:4] 9 table 70. no. of words in a page a nd no. of pages in the eeprom eeprom size page size pcword no. of pages pcpage eeamsb 128 bytes 4 bytes eea[1:0] 32 eea[6:2] 6 161 2543l?avr?08/10 attiny2313 parallel programming parameters, pin mapping, and commands this section describes how to parallel progr am and verify flash program memory, eeprom data memory, memory lock bits, and fuse bits in the attiny2313. pulses are assumed to be at least 250 ns unless otherwise noted. signal names in this section, some pins of the attiny2313 are referenced by signal names describing their functionality during parallel programming, see figure 69 and table 71 . pins not described in the following table are referenced by pin names. the xa1/xa0 pins determine the action executed when the xtal1 pin is given a positive pulse. the bit coding is shown in table 73 . when pulsing wr or oe , the command loaded determines the action executed. the different commands are shown in table 74 . figure 69. parallel programming table 71. pin name mapping signal name in programming mode pin name i/o function rdy/bsy pd1 o 0: device is busy programming, 1: device is ready for new command. oe pd2 i output enable (active low). wr pd3 i write pulse (active low). bs1/pagel pd4 i byte select 1 (?0? select s low byte, ?1? selects high byte). program memory and eeprom data page load. vcc +5v gnd xtal1 pd1 pd2 pd3 pd4 pd5 pd6 pb7 - pb0 data i/o reset +12 v bs1/pagel xa0 xa1/bs2 oe rdy/bsy wr 162 2543l?avr?08/10 attiny2313 xa0 pd5 i xtal action bit 0 xa1/bs2 pd6 i xtal action bit 1. byte select 2 (?0? selects lo w byte, ?1? selects 2?nd high byte). data i/o pb7-0 i/o bi-directional data bus (output when oe is low). table 72. pin values used to enter programming mode pin symbol value xa1 prog_enable[3] 0 xa0 prog_enable[2] 0 bs1 prog_enable[1] 0 wr prog_enable[0] 0 table 73. xa1 and xa0 coding xa1 xa0 action when xtal1 is pulsed 0 0 load flash or eeprom address (high or low address byte determined by bs1). 0 1 load data (high or low data byte for flash determined by bs1). 1 0 load command 1 1 no action, idle table 74. command byte bit coding command byte command executed 1000 0000 chip erase 0100 0000 write fuse bits 0010 0000 write lock bits 0001 0000 write flash 0001 0001 write eeprom 0000 1000 read signature bytes and calibration byte 0000 0100 read fuse and lock bits 0000 0010 read flash 0000 0011 read eeprom table 71. pin name mapping (continued) signal name in programming mode pin name i/o function 163 2543l?avr?08/10 attiny2313 serial programming pin mapping parallel programming enter programming mode the following algorithm puts the device in parallel programming mode: 1. set prog_enable pins listed in table 72 on page 162 to ?0000?, reset pin and v cc to 0v. 2. apply 4.5 - 5.5v between v cc and gnd. 3. ensure that v cc reaches at least 1.8v within the next 20 s. 4. wait 20 - 60 s, and apply 11.5 - 12.5v to reset. 5. keep the prog_enable pins unchanged for at least 10s after the high-voltage has been applied to ensure the prog_enable signature has been latched. 6. wait at least 300 s before giving any parallel programming commands. 7. exit programming m ode by power the device down or by bringing reset pin to 0v. if the rise time of the v cc is unable to fulfill the requiremen ts listed above, th e following alterna- tive algorithm can be used. 1. set prog_enable pins listed in table 72 on page 162 to ?0000?, reset pin to 0v and v cc to 0v. 2. apply 4.5 - 5.5v between v cc and gnd. 3. monitor v cc , and as soon as v cc reaches 0.9 - 1.1v, apply 11.5 - 12.5v to reset. 4. keep the prog_enable pins unchanged for at least 10s after the high-voltage has been applied to ensure the prog_enable signature has been latched. 5. wait until v cc actually reaches 4.5 -5.5v before giving any parallel programming commands. 6. exit programming m ode by power the device down or by bringing reset pin to 0v. considerations for efficient programming the loaded command and address are retained in the device during programming. for efficient programming, the following should be considered. ? the command needs only be loaded once when writing or reading multiple memory locations. ? skip writing the data value 0xff, that is th e contents of the entire eeprom (unless the eesave fuse is programmed) and flash after a chip erase. ? address high byte needs only be loaded before programming or reading a new 256 word window in flash or 2 56 byte eeprom. this consideration also applies to signature bytes reading. chip erase the chip erase will erase the flash and eeprom (1) memories plus lock bits. the lock bits are not reset until the program memory has been completely erased. the fuse bits are not changed. a chip erase must be perfor med before the flas h and/or eeprom are reprogrammed. note: 1. the eeprpom memory is preserved during chip erase if the eesave fuse is programmed. table 75. pin mapping serial programming symbol pins i/o description mosi pb5 i serial data in miso pb6 o serial data out sck pb7 i serial clock 164 2543l?avr?08/10 attiny2313 load command ?chip erase? 1. set xa1, xa0 to ?10?. this enables command loading. 2. set bs1 to ?0?. 3. set data to ?1000 0000?. this is the command for chip erase. 4. give xtal1 a positive pulse. this loads the command. 5. give wr a negative pulse. this starts the chip erase. rdy/bsy goes low. 6. wait until rdy/bsy goes high before loading a new command. 165 2543l?avr?08/10 attiny2313 programming the flash the flash is organized in pages, see table 69 on page 160 . when programming the flash, the program data is latched into a page buffer. this allows one page of program data to be pro- grammed simultaneously. the following procedure describes how to program the entire flash memory: a. load command ?write flash? 1. set xa1, xa0 to ?10?. this enables command loading. 2. set bs1 to ?0?. 3. set data to ?0001 0000?. this is the command for write flash. 4. give xtal1 a positive pulse. this loads the command. b. load address low byte 1. set xa1, xa0 to ?00?. this enables address loading. 2. set bs1 to ?0?. this selects low address. 3. set data = address low byte (0x00 - 0xff). 4. give xtal1 a positive pulse. this loads the address low byte. c. load data low byte 1. set xa1, xa0 to ?01?. this enables data loading. 2. set data = data low byte (0x00 - 0xff). 3. give xtal1 a positive pulse. this loads the data byte. d. load data high byte 1. set bs1 to ?1?. this selects high data byte. 2. set xa1, xa0 to ?01?. this enables data loading. 3. set data = data high byte (0x00 - 0xff). 4. give xtal1 a positive pulse. this loads the data byte. e. repeat b through e unt il the entire buffer is filled or unt il all data within the page is loaded. while the lower bits in the address are mapped to words within the page, the higher bits address the pages within the flash. this is illustrated in figure 70 on page 166 . note that if less than eight bits are required to address words in the page (pagesize < 256), the most significant bit(s) in the address low byte are used to address the page when performing a page write. f. load address high byte 1. set xa1, xa0 to ?00?. this enables address loading. 2. set bs1 to ?1?. this selects high address. 3. set data = address high byte (0x00 - 0xff). 4. give xtal1 a positive pulse. this loads the address high byte. g. program page 1. give wr a negative pulse. this starts programmi ng of the entire page of data. rdy/bsy goes low. 2. wait until rdy/bsy goes high (see figure 71 for signal waveforms). h. repeat b through h until the entire flash is programmed or until all data has been programmed. i. end page programming 1. 1. set xa1, xa0 to ?10?. this enables command loading. 2. set data to ?0000 0000?. this is the command for no operation. 166 2543l?avr?08/10 attiny2313 3. give xtal1 a positive pulse. this loads the command, and the internal write signals are reset. figure 70. addressing the flash which is organized in pages (1) note: 1. pcpage and pcword are listed in table 69 on page 160 . figure 71. programming the flash waveforms (1) note: 1. ?xx? is don?t care. the letters re fer to the programming description above. program memory word address within a page page address within the flash instruction word pag e pcword[pagemsb:0]: 00 01 02 pageend pag e pcword pcpage pcmsb pagemsb program counter rdy/bsy wr oe reset +12v pagel bs2 0x10 addr. low addr. high data data low data high addr. low data low data high xa1 xa0 bs1 xtal1 xx xx xx abcdeb cdegh f 167 2543l?avr?08/10 attiny2313 programming the eeprom the eeprom is organized in pages, see table 70 on page 160 . when programming the eeprom, the program data is latche d into a page buffer. this al lows one page of data to be programmed simultaneously. th e programming algorithm for th e eeprom data memory is as follows (refer to ?programming the flash? on page 165 for details on command, address and data loading): 1. a: load command ?0001 0001?. 2. g: load address high byte (0x00 - 0xff). 3. b: load address low byte (0x00 - 0xff). 4. c: load data (0x00 - 0xff). j: repeat 3 throug h 4 until the entire buffer is filled. k: program eeprom page 1. set bs to ?0?. 2. give wr a negative pulse. this starts pr ogramming of the eeprom page. rdy/bsy goes low. 3. wait until to rdy/bsy goes high before programming the next page (see figure 72 for signal waveforms). figure 72. programming the eeprom waveforms reading the flash the algorithm for reading the flash memory is as follows (refer to ?programming the flash? on page 165 for details on command and address loading): 1. a: load command ?0000 0010?. 2. g: load address high byte (0x00 - 0xff). 3. b: load address low byte (0x00 - 0xff). 4. set oe to ?0?, and bs1 to ?0?. the flash word low byte can now be read at data. 5. set bs to ?1?. the flash word high byte can now be read at data. 6. set oe to ?1?. rdy/bsy wr oe reset +12v pagel bs2 0x11 addr. high data addr. low data addr. low data xx xa1 xa0 bs1 xtal1 xx agbceb c el k 168 2543l?avr?08/10 attiny2313 reading the eeprom the algorithm for reading the eeprom memory is as follows (refer to ?programming the flash? on page 165 for details on command and address loading): 1. a: load command ?0000 0011?. 2. g: load address high byte (0x00 - 0xff). 3. b: load address low byte (0x00 - 0xff). 4. set oe to ?0?, and bs1 to ?0?. the eeprom data byte can now be read at data. 5. set oe to ?1?. programming the fuse low bits the algorithm for programming the fuse low bits is as follows (refer to ?programming the flash? on page 165 for details on command and data loading): 1. a: load command ?0100 0000?. 2. c: load data low byte. bit n = ?0? programs and bit n = ?1? erases the fuse bit. 3. give wr a negative pulse and wait for rdy/bsy to go high. programming the fuse high bits the algorithm for programming the fuse high bits is as follows (refer to ?programming the flash? on page 165 for details on command and data loading): 1. a: load command ?0100 0000?. 2. c: load data low byte. bit n = ?0? programs and bit n = ?1? erases the fuse bit. 3. set bs1 to ?1? and bs2 to ?0?. this selects high data byte. 4. give wr a negative pulse and wait for rdy/bsy to go high. 5. set bs1 to ?0?. this selects low data byte. programming the extended fuse bits the algorithm for programming the extended fuse bits is as follows (refer to ?programming the flash? on page 165 for details on command and data loading): 1. 1. a: load command ?0100 0000?. 2. 2. c: load data low byte. bit n = ?0? programs and bit n = ?1? erases the fuse bit. 3. 3. set bs1 to ?0? and bs2 to ?1?. this selects extended data byte. 4. 4. give wr a negative pulse and wait for rdy/bsy to go high. 5. 5. set bs2 to ?0?. th is selects low data byte. figure 73. programming the fuses waveforms rdy/bsy wr oe reset +12v pagel 0x40 data data xx xa1 xa0 bs1 xtal1 ac 0x40 data xx ac write fuse low byte write fuse high byte 0x40 data xx ac write extended fuse byte bs2 169 2543l?avr?08/10 attiny2313 programming the lock bits the algorithm for programming the lock bits is as follows (refer to ?programming the flash? on page 165 for details on command and data loading): 1. a: load command ?0010 0000?. 2. c: load data low byte. bit n = ?0? programs the lock bit. if lb mode 3 is programmed (lb1 and lb2 is programmed), it is not possible to program the boot lock bits by any external programming mode. 3. give wr a negative pulse and wait for rdy/bsy to go high. the lock bits can only be cleared by executing chip erase. reading the fuse and lock bits the algorithm for reading the fuse and lock bits is as follows (refer to ?programming the flash? on page 165 for details on command loading): 1. a: load command ?0000 0100?. 2. set oe to ?0?, bs2 to ?0? and bs1 to ?0?. the status of the fuse low bits can now be read at data (?0? means programmed). 3. set oe to ?0?, bs2 to ?1? and bs1 to ?1?. the status of the fuse high bits can now be read at data (?0? means programmed). 4. set oe to ?0?, bs2 to ?1?, and bs1 to ?0?. the status of the extended fuse bits can now be read at data (?0? means programmed). 5. set oe to ?0?, bs2 to ?0? and bs1 to ?1?. the status of the lock bits can now be read at data (?0? means programmed). 6. set oe to ?1?. figure 74. mapping between bs1, bs2 and the fuse and lock bits during read reading the signature bytes the algorithm for reading the signatur e bytes is as follows (refer to ?programming the flash? on page 165 for details on command and address loading): 1. a: load command ?0000 1000?. 2. b: load address low byte (0x00 - 0x02). 3. set oe to ?0?, and bs to ?0?. the selected signature byte can now be read at data. 4. set oe to ?1?. lock bits 0 1 bs2 fuse high byte 0 1 bs1 data fuse low byte 0 1 bs2 extended fuse byte 170 2543l?avr?08/10 attiny2313 reading the calibration byte the algorithm for reading the calibrati on byte is as follows (refer to ?programming the flash? on page 165 for details on command and address loading): 1. a: load command ?0000 1000?. 2. b: load address low byte, 0x00. 3. set oe to ?0?, and bs1 to ?1?. the calibration byte can now be read at data. 4. set oe to ?1?. parallel programming characteristics figure 75. parallel programming timing, including some general timing requirements figure 76. parallel programming timing, loading sequence with timing requirements (1) note: 1. the timing requirements shown in figure 75 (i.e., t dvxh , t xhxl , and t xldx ) also apply to loading operation. data & contol (data, xa0/1, bs1, bs2) xtal1 t xhxl t wlwh t dvxh t xldx t plwl t wlrh wr rdy/bsy pagel t phpl t plbx t bvph t xlwl t wlbx t bvwl wlrl xtal1 pagel t plxh xlxh t t xlph addr0 (low byte) data (low byte) data (high byte) addr1 (low byte) data bs1 xa0 xa1 load address (low byte) load data (low byte) load data (high byte) load data load address (low byte) 171 2543l?avr?08/10 attiny2313 figure 77. parallel programming timing, reading sequence (within the same page) with tim- ing requirements (1) note: 1. the timing requirements shown in figure 75 (i.e., t dvxh , t xhxl , and t xldx ) also apply to read- ing operation. table 76. parallel programming characteristics, v cc = 5v 10% symbol parameter min typ max units v pp programming enable voltage 11.5 12.5 v i pp programming enable current 250 a t dvxh data and control valid before xtal1 high 67 ns t xlxh xtal1 low to xtal1 high 200 ns t xhxl xtal1 pulse width high 150 ns t xldx data and control hold after xtal1 low 67 ns t xlwl xtal1 low to wr low 0 ns t xlph xtal1 low to pagel high 0 ns t plxh pagel low to xtal1 high 150 ns t bvph bs1 valid before pagel high 67 ns t phpl pagel pulse width high 150 ns t plbx bs1 hold after pagel low 67 ns t wlbx bs2/1 hold after wr low 67 ns t plwl pagel low to wr low 67 ns t bvwl bs1 valid to wr low 67 ns t wlwh wr pulse width low 150 ns t wlrl wr low to rdy/bsy low 0 1 s t wlrh wr low to rdy/bsy high (1) 3.7 4.5 ms t wlrh_ce wr low to rdy/bsy high for chip erase (2) 7.5 9 ms t xlol xtal1 low to oe low 0 ns xtal1 oe addr0 (low byte) data (low byte) data (high byte) addr1 (low byte) data bs1 xa0 xa1 load address (low byte) read data (low byte) read data (high byte) load address (low byte) t bvdv t oldv t xlol t ohdz 172 2543l?avr?08/10 attiny2313 notes: 1. t wlrh is valid for the write flash, write eepr om, write fuse bits and write lock bits commands. 2. t wlrh_ce is valid for the chip erase command. serial downloading both the flash and eeprom memo ry arrays can be programmed us ing the serial spi bus while reset is pulled to gnd. the serial interface consists of pins sck, mosi (input) and miso (out- put). after reset is set low, the programming enable instruction needs to be executed first before program/erase operations can be executed. note, in table 75 on page 163 , the pin mapping for spi programming is listed. not all pa rts use the spi pins dedicated for the internal spi interface. figure 78. serial programming and verify (1) notes: 1. if the device is clocked by the internal oscill ator, it is no need to connect a clock source to the xtal1 pin. 2. v cc - 0.3v < avcc < v cc + 0.3v, however, avcc should always be within 1.8 - 5.5v when programming the eeprom, an auto-erase cycle is built into the self-timed programming operation (in the serial mode only) and there is no need to first execute the chip erase instruction. the chip erase operation turns the content of every memory location in both the program and eeprom arrays into 0xff. depending on cksel fuses, a valid clock must be present. the minimum low and high periods for the serial clock (sck) input are defined as follows: low:> 2 cpu clock cycles for f ck < 12 mhz, 3 cpu clock cycles for f ck >= 12 mhz high:> 2 cpu clock cycles for f ck < 12 mhz, 3 cpu clock cycles for f ck >= 12 mhz t bvdv bs1 valid to data valid 0 250 ns t oldv oe low to data valid 250 ns t ohdz oe high to data tri-stated 250 ns table 76. parallel programming characteristics, v cc = 5v 10% (continued) symbol parameter min typ max units vcc gnd xtal1 sck miso mosi reset +1.8 - 5.5v 173 2543l?avr?08/10 attiny2313 serial programming algorithm when writing serial data to the attiny2313, data is clocked on the rising edge of sck. when reading data from the attiny2313, data is clocked on the falling edge of sck. see figure 79 , figure 80 and table 79 for timing details. to program and verify the attiny2313 in t he serial programming mo de, the following sequence is recommended (see four byte instruction formats in table 78 on page 174 ): 1. power-up sequence: apply power between v cc and gnd while reset and sck are set to ?0?. in some sys- tems, the programmer can not guarantee that sck is held low during power-up. in this case, reset must be given a positive pulse of at least two cpu clock cycles duration after sck has been set to ?0?. 2. wait for at least 20 ms and enable serial programming by sending the programming enable serial instruction to pin mosi. 3. the serial pr ogramming instructions will not work if the communication is out of synchro- nization. when in sync. the second byte (0x53), will echo back when issuing the third byte of the programming enable instruction. whether the echo is correct or not, all four bytes of the instruction must be transmitted. if the 0x53 did not echo back, give reset a positive pulse and issue a new programming enable command. 4. the flash is programmed one page at a time. the memory page is loaded one byte at a time by supplying the 4 lsb of the address and data together with the load program memory page instruction. to ensure correct loading of the page, the data low byte must be loaded before data high byte is applied for a given address. the program memory page is stored by loading the write program memory page instruction with the 6 msb of the address. if polling ( rdy/bsy ) is not used, the user must wait at least t wd_flash before issuing the next page. (see table 77 on page 174 .) accessing the serial programming interface before the flash write operation completes can result in incorrect programming. 5. a: the eeprom array is program med one byte at a time by supplying the address and data together with the appropriate write instru ction. an eeprom memory location is first automatically erased before new data is written. if polling (rdy/bsy ) is not used, the user must wait at least t wd_eeprom before issuing the next byte. (see table 77 on page 174 .) in a chip erased device, no 0xffs in the data file(s) need to be programmed. b: the eeprom array is programmed one page at a time . the memory page is loaded one byte at a time by supplying the 2 lsb of the address and data together with the load eeprom memory page instruction. the eepro m memory page is stored by loading the write eeprom memory page instruction wit h the 5 msb of the address. when using eeprom page access only byte location s loaded with the load eeprom memory page instruction is altered. th e remaining locations rema in unchanged. if polling ( rdy/bsy ) is not used, the used must wait at least t wd_eeprom before issuing the next page (see table 77 on page 174 ). in a chip erased device, no 0xff in the data file(s) need to be programmed. 6. any memory location can be verified by using the read instruction which returns the con- tent at the selected addr ess at serial output miso. 7. at the end of the pr ogramming session, reset can be set high to commence normal operation. 8. power-off sequence (if needed): set reset to ?1?. turn v cc power off. 174 2543l?avr?08/10 attiny2313 figure 79. serial programming waveforms table 77. minimum wait delay befo re writing the next fl ash or eeprom location symbol minimum wait delay t wd_flash 4.5 ms t wd_eeprom 4.0 ms t wd_erase 9.0 ms t wd_fuse 4.5 ms msb msb lsb lsb serial clock input (sck) serial data input (mosi) (miso) sample serial data output table 78. serial programming instruction set instruction instruction format operation byte 1 byte 2 byte 3 byte4 programming enable 1010 1100 0101 0011 xxxx xxxx xxxx xxxx enable serial programming after reset goes low. chip erase 1010 1100 100x xxxx xxxx xxxx xxxx xxxx chip erase eeprom and flash. read program memory 0010 h 000 0000 00 aa bbbb bbbb oooo oooo read h (high or low) data o from program memory at word address a : b . load program memory page 0100 h 000 000x xxxx xxxx bbbb iiii iiii write h (high or low) data i to program memory page at word address b . data low byte must be loaded before data high byte is applied within the same address. write program memory page 0100 1100 0000 00 aa bbbb xxxx xxxx xxxx write program memory page at address a : b . read eeprom memory 1010 0000 000x xxxx x bbb bbbb oooo oooo read data o from eeprom memory at address b . write eeprom memory 1100 0000 000x xxxx x bbb bbbb iiii iiii write data i to eeprom memory at address b . load eeprom memory page (page access) 1100 0001 0000 0000 0000 00 bb iiii iiii load data i to eeprom memory page buffer. after data is loaded, program eeprom page. write eeprom memory page (page access) 1100 0010 00xx xxxx x bbb bb 00 xxxx xxxx write eeprom page at address b . 175 2543l?avr?08/10 attiny2313 note: a = address high bits, b = address low bits, h = 0 - low byte, 1 - high byte, o = data out, i = data in, x = don?t care read lock bits 0101 1000 0000 0000 xxxx xxxx xx oo oooo read lock bits. ?0? = programmed, ?1? = unprogrammed. see table 64 on page 158 for details. write lock bits 1010 1100 111x xxxx xxxx xxxx 11 ii iiii write lock bits. set bits = ?0? to program lock bits. see table 64 on page 158 for details. read signature byte 0011 0000 000x xxxx xxxx xx bb oooo oooo read signature byte o at address b . write fuse bits 1010 1100 1010 0000 xxxx xxxx iiii iiii set bits = ?0? to program, ?1? to unprogram. write fuse high bits 1010 1100 1010 1000 xxxx xxxx iiii iiii set bits = ?0? to program, ?1? to unprogram. write extended fuse bits 1010 1100 1010 0100 xxxx xxxx xxxx xxx i set bits = ?0? to program, ?1? to unprogram. read fuse bits 0101 0000 0000 0000 xxxx xxxx oooo oooo read fuse bits. ?0? = programmed, ?1? = unprogrammed. read fuse high bits 0101 1000 0000 1000 xxxx xxxx oooo oooo read fuse high bits. ?0? = pro- grammed, ?1? = unprogrammed. read extended fuse bits 0101 0000 0000 1000 xxxx xxxx oooo oooo read extended fuse bits. ?0? = pro- grammed, ?1? = unprogrammed. read calibration byte 0011 1000 000x xxxx 0000 000 b oooo oooo read calibration byte at address b . poll rdy/bsy 1111 0000 0000 0000 xxxx xxxx xxxx xxx o if o = ?1?, a programming operation is still busy. wait until this bit returns to ?0? before applying another command. table 78. serial programming instruction set instruction instruction format operation byte 1 byte 2 byte 3 byte4 176 2543l?avr?08/10 attiny2313 serial programming characteristics figure 80. serial programming timing note: 1. 2 t clcl for f ck < 12 mhz, 3 t clcl for f ck >= 12 mhz table 79. serial programming characteristics, t a = -40 c to +85 c, v cc = 2.7v - 5.5v (unless otherwise noted) symbol parameter min typ max units 1/t clcl oscillator frequency (attiny2313l) 0 10 mhz t clcl oscillator period (attiny2313l) 125 ns 1/t clcl oscillator frequency (attiny2313, v cc = 4.5v - 5.5v) 0 20 mhz t clcl oscillator period (attiny2313, v cc = 4.5v - 5.5v) 67 ns t shsl sck pulse width high 2 t clcl * ns t slsh sck pulse width low 2 t clcl * ns t ovsh mosi setup to sck high t clcl ns t shox mosi hold after sck high 2 t clcl ns t sliv sck low to miso valid 100 ns mosi miso sck t ovsh t shsl t slsh t shox t sliv 177 2543l?avr?08/10 attiny2313 electrical characteristics absolute maximum ratings* dc characteristics operating temperature.................................. -55 c to +125 c *notice: stresses beyond those listed under ?absolute maximum ratings? may cause permanent dam- age to the device. this is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of th is specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. storage temperature ..................................... -65c to +150c voltage on any pin except reset with respect to ground ................................-0.5v to v cc +0.5v voltage on reset with respect to ground......-0.5v to +13.0v maximum operating voltage ............................................ 6.0v dc current per i/o pin ............................................... 40.0 ma dc current v cc and gnd pins ................................ 200.0 ma t a = -40 c to +85 c, v cc = 1.8v to 5.5v (unless otherwise noted) (1) symbol parameter condition min. typ. (2) max. units v il input low voltage except xtal1 and reset pin v cc = 1.8v - 2.4v v cc = 2.4v - 5.5v -0.5 0.2v cc (3) 0.3v cc (3) v v ih input high-voltage except xtal1 and reset pins v cc = 1.8v - 2.4v v cc = 2.4v - 5.5v 0.7v cc (4) 0.6v cc (4) v cc +0.5 v v il1 input low voltage xtal1 pin v cc = 1.8v - 5.5v -0.5 0.1v cc (3) v v ih1 input high-voltage xtal1 pin v cc = 1.8v - 2.4v v cc = 2.4v - 5.5v 0.8v cc (4) 0.7v cc (4) v cc +0.5 v v il2 input low voltage reset pin v cc = 1.8v - 5.5v -0.5 0.2v cc (3) v v ih2 input high-voltage reset pin v cc = 1.8v - 5.5v 0.9v cc (4) v cc +0.5 v v il3 input low voltage reset pin as i/o v cc = 1.8v - 2.4v v cc = 2.4v - 5.5v -0.5 0.2v cc (3) 0.3v cc (3) v v ih3 input high-voltage reset pin as i/o v cc = 1.8v - 2.4v v cc = 2.4v - 5.5v 0.7v cc (4) 0.6v cc (4) v cc +0.5 v v ol output low voltage (5) (port a, port b, port d) i ol = 20 ma, v cc = 5v i ol = 10 ma, v cc = 3v 0.7 0.5 v v v oh output high-voltage (6) (port a, port b, port d) i oh = -20 ma, v cc = 5v i oh = -10 ma, v cc = 3v 4.2 2.5 v v i il input leakage current i/o pin v cc = 5.5v, pin low (absolute value) 1a i ih input leakage current i/o pin v cc = 5.5v, pin high (absolute value) 1a r rst reset pull-up resistor 30 60 k r pu i/o pin pull-up resistor 20 50 k 178 2543l?avr?08/10 attiny2313 notes: 1. all dc characteristics contained in this data sheet ar e based on simulation and characterization of other avr microcon- trollers manufactured in the same process technology. these values are preliminary values representing design targets, and will be updated after characterization of actual silicon. 2. typical values at +25 c. 3. ?max? means the highest value where the pin is guaranteed to be read as low. 4. ?min? means the lowest value where th e pin is guaranteed to be read as high. 5. although each i/o port can sink more than the test conditions (10 ma at v cc = 5v, 5 ma at v cc = 3v) under steady state conditions (non-transient), t he following must be observed: 1] the sum of all iol, for al l ports, should not exceed 60 ma. if iol exceeds the test conditio n, vol may exceed the related sp ecification. pins ar e not guaranteed to sink current greater than the listed test condition. 6. although each i/o port can source more than the test conditions (10 ma at v cc = 5v, 5 ma at v cc = 3v) under steady state conditions (non-transient), t he following must be observed: 1] the sum of all ioh, for all ports, should not exceed 60 ma. if ioh exceeds the test condition, voh may exceed the relat ed specification. pins are not guaranteed to source current greater than the listed test condition. i cc power supply current active 1mhz, v cc = 2v 0.35 ma active 4mhz, v cc = 3v 2 ma active 8mhz, v cc = 5v 6 ma idle 1mhz, v cc = 2v 0.08 0.2 ma idle 4mhz, v cc = 3v 0.41 1 ma idle 8mhz, v cc = 5v 1.6 3 ma power-down mode wdt enabled, v cc = 3v < 3 6 a wdt disabled, v cc = 3v < 0.5 2 a v acio analog comparator input offset voltage v cc = 5v v in = v cc /2 < 10 40 mv i aclk analog comparator input leakage current v cc = 5v v in = v cc /2 -50 50 na t acpd analog comparator propagation delay v cc = 2.7v v cc = 5.0v 750 500 ns t a = -40 c to +85 c, v cc = 1.8v to 5.5v (unless otherwise noted) (1) (continued) symbol parameter condition min. typ. (2) max. units 179 2543l?avr?08/10 attiny2313 external clock drive waveforms figure 81. external clock drive waveforms external clock drive v il1 v ih1 table 80. external clock drive (estimated values) symbol parameter v cc = 1.8 - 5.5v v cc = 2.7 - 5.5v v cc = 4.5 - 5.5v units min. max. min. max. min. max. 1/t clcl oscillator frequency 0 4 010020mhz t clcl clock period 250 100 50 ns t chcx high time 100 40 20 ns t clcx low time 100 40 20 ns t clch rise time 2.0 1.6 0.5 s t chcl fall time 2.0 1.6 0.5 s t clcl change in period from one clock cycle to the next 222% 180 2543l?avr?08/10 attiny2313 maximum speed vs. v cc maximum frequency is dependent on v cc. as shown in figure 82 and figure 83 , the maximum frequency vs. v cc curve is linear between 1.8v < v cc < 2.7v and between 2.7v < v cc < 4.5v. figure 82. maximum frequency vs. v cc , attiny2313v figure 83. maximum frequency vs. v cc , attiny2313 10 mhz 4 mhz 1.8v 2.7v 5.5v safe operating area 20 mhz 10 mhz 2.7v 4.5v 5.5v safe operating area 181 2543l?avr?08/10 attiny2313 attiny2313 typical characteristics the following charts show typical behavior. t hese figures are not tested during manufacturing. all current consumption measurements are perfor med with all i/o pins configured as inputs and with internal pull-ups enabled. a sine wave generator with rail-to-rail output is used as clock source. the power consumption in power-down mode is independent of clock selection. the current consumption is a f unction of several factors such as: operating voltage, operating frequency, loading of i/o pins, switching rate of i/o pins, code executed and ambient tempera- ture. the dominating factors are operating voltage and frequency. the current drawn from capacitive loaded pins may be estimated (for one pin) as c l * v cc *f where c l = load capacitance, v cc = operating voltage and f = average switching frequency of i/o pin. the parts are characterized at frequencies higher than test lim its. parts are not guaranteed to function properly at frequencies hig her than the ordering code indicates. the difference between current consumption in power-down mode with watchdog timer enabled and power-down mode with watchdog timer disabled represents t he differential cur- rent drawn by the watchdog timer. active supply current figure 84. active supply current vs. frequency (0.1 - 1.0 mhz) active supply current vs. low frequency 0.1 - 1.0 mhz 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 0.2 0.4 0.6 0.8 1 1.2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 frequency (mhz) i cc (ma) 182 2543l?avr?08/10 attiny2313 figure 85. active supply current vs. frequency (1 - 20 mhz) figure 86. active supply current vs. v cc (internal rc oscillator, 8 mhz) active supply current vs. frequency 1 - 20 mhz 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 2 4 6 8 10 12 14 02468101214161820 frequency (mhz) i cc (ma) active supply current vs. v cc internal rc oscillator, 8 mhz 85 ?c 25 ?c -40 ?c 0 1 2 3 4 5 6 7 8 9 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 183 2543l?avr?08/10 attiny2313 figure 87. active supply current vs. v cc (internal rc oscillator, 4 mhz) figure 88. active supply current vs. v cc (internal rc oscillator, 1 mhz) active supply current vs. v cc internal rc oscillator, 4 mhz 85 c 25 c -40 c 0 1 2 3 4 5 6 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) active supply current vs. v cc internal rc oscillator, 1 mhz 85 c 25 c -40 c 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 184 2543l?avr?08/10 attiny2313 figure 89. active supply current vs. v cc (internal rc oscillator, 0.5 mhz) figure 90. active supply current vs. v cc (internal rc oscillator, 128 khz) active supply current vs. v cc internal rc oscillator, 0.5 mhz 85 c 25 c -40 c 0 0.2 0.4 0.6 0.8 1 1.2 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) active supply current vs. v cc internal rc oscillator, 128 khz 85 c 25 c -40 c 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 v cc (v) i cc (ma) 185 2543l?avr?08/10 attiny2313 idle supply current figure 91. idle supply current vs. frequency (0.1 - 1.0 mhz) figure 92. idle supply current vs. frequency (1 - 20 mhz) idle supply current vs. frequency 0.1 - 1.0 mhz 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 0.05 0.1 0.15 0.2 0.25 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 frequency (mhz) i cc (m a) idle supply current vs. frequency 1 - 20 mhz 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 2 4 6 8 101214161820 frequency (mhz) i cc (ma) 186 2543l?avr?08/10 attiny2313 figure 93. idle supply current vs. v cc (internal rc oscillator, 8 mhz) figure 94. idle supply current vs. v cc (internal rc oscillator, 4 mhz) idle supply current vs. v cc internal rc oscillator, 8 mhz 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) idle supply current vs. v cc internal rc oscillator, 4 mhz 85 c 25 c -40 c 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 187 2543l?avr?08/10 attiny2313 figure 95. idle supply current vs. v cc (internal rc oscillator, 1 mhz) figure 96. idle supply current vs. v cc (internal rc osc illator, 0.5 mhz) idle supply current vs. v cc internal rc oscillator, 1 mhz 85 c 25 c -40 c 0 0.1 0.2 0.3 0.4 0.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) idle supply current vs. v cc internal rc oscillator, 0.5 mhz 85 c 25 c -40 c 0 0.05 0.1 0.15 0.2 0.25 0.3 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 188 2543l?avr?08/10 attiny2313 figure 97. idle supply current vs. v cc (internal rc osc illator, 128 khz) power-down supply current figure 98. power-down supply current vs. v cc (watchdog timer disabled) idle supply current vs. v cc internal rc oscillator, 128 khz 85 c 25 c -40 c 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (m a) power-down supply current vs. v cc watchdog timer disabled 85 c 25 c -40 c 0 0.25 0.5 0.75 1 1.25 1.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 189 2543l?avr?08/10 attiny2313 figure 99. power-down supply current vs. v cc (watchdog timer enabled) standby supply current figure 100. standby supply current vs. v cc power-down supply current vs. v cc watchdog timer enabled 85 c 25 c -40 c 0 2 4 6 8 10 12 14 16 18 20 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) standby supply current vs. v cc 455khz res 2mhz xtal 2mhz res 1mhz res 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (m a) 190 2543l?avr?08/10 attiny2313 pin pull-up figure 101. i/o pin pull-up resistor current vs. input voltage (v cc = 5v) figure 102. i/o pin pull-up resistor current vs. input voltage (v cc = 2.7v) i/o pin pull-up resistor current vs. input voltage vcc = 5v 85 c 25 c -40 c 0 20 40 60 80 100 120 140 160 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 v op (v) i op (ua ) i/o pin pull-up resistor current vs. input voltage vcc = 2.7v 85 c 25 c -40 c 0 10 20 30 40 50 60 70 80 0 0.5 1 1.5 2 2.5 3 v op (v) i op (ua) 191 2543l?avr?08/10 attiny2313 figure 103. reset pull-up resistor current vs. reset pin voltage (v cc = 5v) figure 104. reset pull-up resistor current vs. reset pin voltage (v cc = 2.7v) reset pull-up resistor current vs. reset pin voltage vcc = 5v 85 c 25 c -40 c 0 20 40 60 80 100 120 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 v reset (v) i reset (ua) reset pull-up resistor current vs. reset pin voltage v cc = 2.7v 85 c 25 c -40 c 0 10 20 30 40 50 60 0 0.5 1 1.5 2 2.5 3 v reset (v) i reset (ua) 192 2543l?avr?08/10 attiny2313 pin driver strength figure 105. i/o pin source current vs. output voltage (v cc = 5v) figure 106. i/o pin source current vs. output voltage (v cc = 2.7v) i/o pin source current vs. output voltage vcc = 5v 85 c 25 c -40 c 0 10 20 30 40 50 60 70 80 90 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 v oh (v) i oh (ma) i/o pin source current vs. output voltage vcc = 2.7v 85 c 25 c -40 c 0 5 10 15 20 25 30 35 0.5 1 1.5 2 2.5 3 v oh (v) i oh (ma) 193 2543l?avr?08/10 attiny2313 figure 107. i/o pin source current vs. output voltage (v cc = 1.8v) figure 108. i/o pin sink current vs. output voltage (v cc = 5v) i/o pin source current vs. output voltage v cc = 1.8v 85 c 25 c -40 c 0 1 2 3 4 5 6 7 8 9 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v oh (v) i oh (ma) i/o pin sink current vs. output voltage v cc = 5v 85 c 25 c -40 c 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v ol (v) i ol (ma) 194 2543l?avr?08/10 attiny2313 figure 109. i/o pin sink current vs. output voltage (v cc = 2.7v) figure 110. i/o pin sink current vs. output voltage (v cc = 1.8v) i/o pin sink current vs. output voltage v cc = 2.7v 85 c 25 c -40 c 0 5 10 15 20 25 30 35 40 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v ol (v) i ol (ma) i/o pin sink current vs. output voltage v cc = 1.8v 85 c 25 c -40 c 0 2 4 6 8 10 12 14 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 v ol (v) i ol (ma) 195 2543l?avr?08/10 attiny2313 figure 111. reset i/o pin sour ce current vs. output voltage (v cc = 5v) figure 112. reset i/o pin source curr ent vs. output voltage (v cc = 2.7v) reset i/o pin source current vs. output voltage v cc = 5v 85 c 25 c -40 c 0 2 4 6 8 10 12 14 16 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 v oh (v) current (ma) reset i/o pin source current vs. output voltage v cc = 2.7v 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 0.5 1 1.5 2 2.5 3 v oh (v) current (m a) 196 2543l?avr?08/10 attiny2313 figure 113. reset i/o pin source curr ent vs. output voltage (v cc = 1.8v) figure 114. reset i/o pin sink current vs. output voltage (v cc = 5v) reset i/o pin source current vs. output voltage v cc = 1.8v 85 c 25 c -40 c 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v oh (v) current (ma) reset i/o pin sink current vs. output voltage v cc = 5v 85 c 25 c -40 c 0 2 4 6 8 10 12 14 16 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 v ol (v) current (ma) 197 2543l?avr?08/10 attiny2313 figure 115. reset i/o pin sink current vs. output voltage (v cc = 2.7v) figure 116. reset i/o pin sink current vs. output voltage (v cc = 1.8v) reset i/o pin sink current vs. output voltage v cc = 2.7v 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 v ol (v) current (ma) reset i/o pin sink current vs. output voltage v cc = 1.8v 85 c 25 c -40 c 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 v ol (v) current (ma) 198 2543l?avr?08/10 attiny2313 pin thresholds and hysteresis figure 117. i/o pin input threshold voltage vs. v cc (v ih , i/o pin read as ?1?) figure 118. i/o pin input threshold voltage vs. v cc (v il , i/o pin read as ?0?) i/o pin input threshold voltage vs. v cc vih, io pin read as '1' 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) i/o pin input threshold voltage vs. v cc vil, io pin read as '0' 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) 199 2543l?avr?08/10 attiny2313 figure 119. reset i/o input threshold voltage vs. v cc (v ih ,reset pin read as ?1?) figure 120. reset i/o input threshold voltage vs. v cc (v il ,reset pin read as ?0?) reset i/o pin input threshold voltage vs. v cc vih, io pin read as '1' 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) reset i/o pin input threshold voltage vs. v cc vil, io pin read as '0' 85c 25c -40c 0 0.5 1 1.5 2 2.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) 200 2543l?avr?08/10 attiny2313 figure 121. reset i/o input pin hysteresis vs. v cc figure 122. reset input thresh old voltage vs. v cc (v ih ,reset pin read as ?1?) reset i/o input pin hysteresis vs. v cc 85 c 25 c -40 c 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) input hysteresis (v) reset input threshold voltage vs. v cc vih, io pin read as '1' 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) 201 2543l?avr?08/10 attiny2313 figure 123. reset input thresh old voltage vs. v cc (v il ,reset pin read as ?0?) figure 124. reset input pin hysteresis vs. v cc reset input threshold voltage vs. v cc vil, io pin read as '0' 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) reset input pin hysteresis vs. v cc 85 c 25 c -40 c 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) input hysteresis (v) 202 2543l?avr?08/10 attiny2313 bod thresholds and analog comparator offset figure 125. bod thresholds vs. temperature (bod level is 4.3v) figure 126. bod thresholds vs. temperature (bod level is 2.7v) bod thresholds vs. temperature bodlevel is 4.3v 4.25 4.3 4.35 4.4 4.45 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 temperature (c) thres hol d (v ) rising vcc falling vcc bod thresholds vs. temperature bodlevel is 2.7v 2.65 2.7 2.75 2.8 2.85 -40-30-20-100 102030405060708090 temperature (c) threshold (v) rising vcc falling vcc 203 2543l?avr?08/10 attiny2313 figure 127. bod thresholds vs. temperature (bod level is 1.8v) internal oscillator speed figure 128. watchdog oscillator frequency vs. v cc bod thresholds vs. temperature bodlevel is 1.8v rising vcc falling vcc 1.78 1.8 1.82 1.84 1.86 1.88 -40-30-20-100 102030405060708090 temperature (c) threshold (v) watchdog oscillator frequency vs. vcc 85 c 25 c -40 c 0.095 0.096 0.097 0.098 0.099 0.1 0.101 0.102 0.103 0.104 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) f rc (m hz ) 204 2543l?avr?08/10 attiny2313 figure 129. watchdog oscillator freq uency vs. temperature figure 130. calibrated 8 mhz rc oscillator frequen cy vs. temperature watchdog oscillator frequency vs. temperature 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0.096 0.097 0.098 0.099 0.1 0.101 0.102 0.103 0.104 0.105 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 temperature (c) f rc (mhz) calibrated 8mhz rc oscillator frequency vs. temperature 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 -40-30-20-100 102030405060708090 temperature (c) f rc (mhz ) 205 2543l?avr?08/10 attiny2313 figure 131. calibrated 8 mhz rc osc illator frequency vs. v cc figure 132. calibrated 8 mhz rc oscillator frequen cy vs. osccal value calibrated 8mhz rc oscillator frequency vs. v cc 85 c 25 c -40 c 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) f rc (mhz) calibrated 8mhz rc oscillator frequency vs. osccal value 25 c 0 2 4 6 8 10 12 14 0 163248648096112128 osccal value f rc (mhz) 206 2543l?avr?08/10 attiny2313 figure 133. calibrated 4 mhz rc oscillator frequen cy vs. temperature figure 134. calibrated 4 mhz rc osc illator frequency vs. v cc calibrated 4mhz rc oscillator frequency vs. temperature 5.5 v 5.0 v 3.3 v 1.8 v 3.9 3.95 4 4.05 4.1 4.15 4.2 -40-30-20-10 0 102030405060708090 temperature (c) f rc (mhz) calibrated 4mhz rc oscillator frequency vs. v cc 85 c 25 c -40 c 3.9 3.95 4 4.05 4.1 4.15 4.2 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) f rc (mhz) 207 2543l?avr?08/10 attiny2313 figure 135. calibrated 4 mhz rc oscillator frequen cy vs. osccal value current consumption of peripheral units figure 136. brownout detector current vs. v cc calibrated 4mhz rc oscillator frequency vs. osccal value 25 c 0 1 2 3 4 5 6 7 0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 osccal value f rc (mhz ) brownout detector current vs. v cc 85 c 25 c -40 c 0 5 10 15 20 25 30 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 208 2543l?avr?08/10 attiny2313 figure 137. analog comparator current vs. v cc figure 138. programming current vs. v cc analog comparator current vs. v cc 85 c 25 c -40 c 0 10 20 30 40 50 60 70 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) programming current vs. v cc 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 209 2543l?avr?08/10 attiny2313 current consumption in reset and reset pulsewidth figure 139. reset supply current vs. v cc (0.1 - 1.0 mhz, excluding current through the reset pull-up) figure 140. reset supply current vs. v cc (1 - 20 mhz, excluding current through the reset pull-up) reset supply current vs. v cc 0.1 - 1.0 mhz, excluding current through the reset pullup 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 frequency (mhz) i cc (ma) reset supply current vs. v cc 1 - 20 mhz, excluding current through the reset pullup 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 0 0.5 1 1.5 2 2.5 0 2 4 6 8 101214161820 frequency (mhz) i cc (ma) 210 2543l?avr?08/10 attiny2313 figure 141. minimum reset pulse width vs. v cc minimum reset pulse width vs. v cc 85 c 25 c -40 c 0 500 1000 1500 2000 2500 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) pulsewidth (ns) 211 2543l?avr?08/10 attiny2313 register summary address name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 page 0x3f (0x5f) sreg i t h s v n z c 8 0x3e (0x5e) reserved ? ? ? ? ? ? ? ? 0x3d (0x5d) spl sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0 11 0x3c (0x5c) ocr0b timer/counter0 ? compare register b 77 0x3b (0x5b) gimsk int1 int0 pcie ? ? ? ? ?60 0x3a (0x5a) eifr intf1 intf0 pcif ? ? ? ? ?61 0x39 (0x59) timsk toie1 ocie1a ocie1b ? icie1 ocie0b toie0 ocie0a 78, 109 0x38 (0x58) tifr tov1 ocf1a ocf1b ? icf1 ocf0b tov0 ocf0a 78 0x37 (0x57) spmcsr ? ? ? ctpb rflb pgwrt pgers selfprgen 155 0x36 (0x56) ocr0a timer/counter0 ? compare register a 77 0x35 (0x55) mcucr pud sm1 se sm0 isc11 isc10 isc01 isc00 53 0x34 (0x54) mcusr ? ? ? ? wdrf borf extrf porf 37 0x33 (0x53) tccr0b foc0a foc0b ? ? wgm02 cs02 cs01 cs00 76 0x32 (0x52) tcnt0 timer/counter0 (8-bit) 77 0x31 (0x51) osccal ? cal6 cal5 cal4 cal3 cal2 cal1 cal0 26 0x30 (0x50) tccr0a com0a1 com0a0 com0b1 com0b0 ? ?wgm01wgm00 73 0x2f (0x4f) tccr1a com1a1 com1a0 com1b1 com1bo ? ? wgm11 wgm10 104 0x2e (0x4e) tccr1b icnc1 ices1 ? wgm13 wgm12 cs12 cs11 cs10 107 0x2d (0x4d) tcnt1h timer/counter1 ? counter register high byte 108 0x2c (0x4c) tcnt1l timer/counter1 ? counter register low byte 108 0x2b (0x4b) ocr1ah timer/counter1 ? compare register a high byte 108 0x2a (0x4a) ocr1al timer/counter1 ? compare register a low byte 108 0x29 (0x49) ocr1bh timer/counter1 ? compare register b high byte 109 0x28 (0x48) ocr1bl timer/counter1 ? compare register b low byte 109 0x27 (0x47) reserved ? ? ? ? ? ? ? ? 0x26 (0x46) clkpr clkpce ? ? ? clkps3 clkps2 clkps1 clkps0 28 0x25 (0x45) icr1h timer/counter1 - input capture register high byte 109 0x24 (0x44) icr1l timer/counter1 - input capture register low byte 109 0x23 (0x43) gtccr ? ? ? ? ? ? ? psr10 81 0x22 (ox42) tccr1c foc1a foc1b ? ? ? ? ? ? 108 0x21 (0x41) wdtcsr wdif wdie wdp3 wdce wde wdp2 wdp1 wdp0 42 0x20 (0x40) pcmsk pcint7 pcint6 pcint 5 pcint4 pcint3 pcint2 pcint1 pcint0 61 0x1f (0x3f) reserved ? ? ? ? ? ? ? ? 0x1e (0x3e) eear ? eeprom address register 16 0x1d (0x3d) eedr eeprom data register 17 0x1c (0x3c) eecr ? ? eepm1 eepm0 eerie eempe eepe eere 17 0x1b (0x3b) porta ? ? ? ? ? porta2 porta1 porta0 58 0x1a (0x3a) ddra ? ? ? ? ? dda2 dda1 dda0 58 0x19 (0x39) pina ? ? ? ? ? pina2 pina1 pina0 58 0x18 (0x38) portb portb7 portb6 portb5 portb4 portb3 portb2 portb1 portb0 58 0x17 (0x37) ddrb ddb7 ddb6 ddb5 ddb4 ddb3 ddb2 ddb1 ddb0 58 0x16 (0x36) pinb pinb7 pinb6 pinb5 pinb4 pinb3 pinb2 pinb1 pinb0 58 0x15 (0x35) gpior2 general purpose i/o register 2 21 0x14 (0x34) gpior1 general purpose i/o register 1 21 0x13 (0x33) gpior0 general purpose i/o register 0 21 0x12 (0x32) portd ? portd6 portd5 portd4 portd3 portd2 portd1 portd0 58 0x11 (0x31) ddrd ? ddd6 ddd5 ddd4 ddd3 ddd2 ddd1 ddd0 58 0x10 (0x30) pind ? pind6 pind5 pind4 pind3 pind2 pind1 pind0 58 0x0f (0x2f) usidr usi data register 144 0x0e (0x2e) usisr usisif usioif usipf usidc usicnt3 usicnt2 usicnt1 usicnt0 145 0x0d (0x2d) usicr usisie usioie usiwm1 usiwm0 usics1 usics0 usiclk usitc 145 0x0c (0x2c) udr uart data register (8-bit) 129 0x0b (0x2b) ucsra rxc txc udre fe dor upe u2x mpcm 129 0x0a (0x2a) ucsrb rxcie txcie udrie rxen txen ucsz2 rxb8 txb8 131 0x09 (0x29) ubrrl ubrrh[7:0] 133 0x08 (0x28) acsr acd acbg aco aci acie acic acis1 acis0 149 0x07 (0x27) reserved ? ? ? ? ? ? ? ? 0x06 (0x26) reserved ? ? ? ? ? ? ? ? 0x05 (0x25) reserved ? ? ? ? ? ? ? ? 0x04 (0x24) reserved ? ? ? ? ? ? ? ? 0x03 (0x23) ucsrc ? umsel upm1 upm0 usbs ucsz1 ucsz0 ucpol 132 0x02 (0x22) ubrrh ? ? ? ? ubrrh[11:8] 133 0x01 (0x21) didr ? ? ? ? ? ? ain1d ain0d 150 0x00 (0x20) reserved ? ? ? ? ? ? ? ? 212 2543l?avr?08/10 attiny2313 note: 1. for compatibility with future devices, reserved bits should be written to zero if accessed. reserved i/o memory addresse s should never be written. 2. i/o registers within the address range 0x00 - 0x1f are direct ly bit-accessible using the sbi and cbi instructions. in these registers, the value of single bits can be ch ecked by using the sbis and sbic instructions. 3. some of the status flags are cleared by writing a logical one to them. note that, unlike most other avrs, the cbi and sbi instructions will only operate on the specif ied bit, and can therefore be used on regi sters containing such status flags. the cbi and sbi instructions work wit h registers 0x00 to 0x1f only. 4. when using the i/o specific commands in and out, t he i/o addresses 0x00 - 0x3f must be used. when addressing i/o registers as data space using ld and st instructions, 0x20 must be added to these addresses. 213 2543l?avr?08/10 attiny2313 instruction set summary mnemonics operands description operation flags #clocks arithmetic and logic instructions add rd, rr add two registers rd rd + rr z,c,n,v,h 1 adc rd, rr add with carry two registers rd rd + rr + c z,c,n,v,h 1 adiw rdl,k add immediate to word rdh:rdl rdh:rdl + k z,c,n,v,s 2 sub rd, rr subtract two registers rd rd - rr z,c,n,v,h 1 subi rd, k subtract constant from register rd rd - k z,c,n,v,h 1 sbc rd, rr subtract with carry two registers rd rd - rr - c z,c,n,v,h 1 sbci rd, k subtract with carry constant from reg. rd rd - k - c z,c,n,v,h 1 sbiw rdl,k subtract immediate from word rdh:rdl rdh:rdl - k z,c,n,v,s 2 and rd, rr logical and registers rd rd ? rr z,n,v 1 andi rd, k logical and register and constant rd rd ? k z,n,v 1 or rd, rr logical or registers rd rd v rr z,n,v 1 ori rd, k logical or register and constant rd rd v k z,n,v 1 eor rd, rr exclusive or registers rd rd rr z,n,v 1 com rd one?s complement rd 0xff ? rd z,c,n,v 1 neg rd two?s complement rd 0x00 ? rd z,c,n,v,h 1 sbr rd,k set bit(s) in register rd rd v k z,n,v 1 cbr rd,k clear bit(s) in register rd rd ? (0xff - k) z,n,v 1 inc rd increment rd rd + 1 z,n,v 1 dec rd decrement rd rd ? 1 z,n,v 1 tst rd test for zero or minus rd rd ? rd z,n,v 1 clr rd clear register rd rd rd z,n,v 1 ser rd set register rd 0xff none 1 branch instructions rjmp k relative jump pc pc + k + 1 none 2 ijmp indirect jump to (z) pc z none 2 rcall k relative subroutine call pc pc + k + 1 none 3 icall indirect call to (z) pc znone3 ret subroutine return pc stack none 4 reti interrupt return pc stack i 4 cpse rd,rr compare, skip if equal if (rd = rr) pc pc + 2 or 3 none 1/2/3 cp rd,rr compare rd ? rr z, n,v,c,h 1 cpc rd,rr compare with carry rd ? rr ? c z, n,v,c,h 1 cpi rd,k compare register with immediate rd ? k z, n,v,c,h 1 sbrc rr, b skip if bit in register cleared if (rr(b)=0) pc pc + 2 or 3 none 1/2/3 sbrs rr, b skip if bit in register is set if (rr(b)=1) pc pc + 2 or 3 none 1/2/3 sbic p, b skip if bit in i/o register cleared if (p(b)=0) pc pc + 2 or 3 none 1/2/3 sbis p, b skip if bit in i/o register is set if (p(b)=1) pc pc + 2 or 3 none 1/2/3 brbs s, k branch if status flag set if (sreg(s) = 1) then pc pc+k + 1 none 1/2 brbc s, k branch if status flag cleared if (sreg(s) = 0) then pc pc+k + 1 none 1/2 breq k branch if equal if (z = 1) then pc pc + k + 1 none 1/2 brne k branch if not equal if (z = 0) then pc pc + k + 1 none 1/2 brcs k branch if carry set if (c = 1) then pc pc + k + 1 none 1/2 brcc k branch if carry cleared if (c = 0) then pc pc + k + 1 none 1/2 brsh k branch if same or higher if (c = 0) then pc pc + k + 1 none 1/2 brlo k branch if lower if (c = 1) then pc pc + k + 1 none 1/2 brmi k branch if minus if (n = 1) then pc pc + k + 1 none 1/2 brpl k branch if plus if (n = 0) then pc pc + k + 1 none 1/2 brge k branch if greater or equal, signed if (n v= 0) then pc pc + k + 1 none 1/2 brlt k branch if less than zero, signed if (n v= 1) then pc pc + k + 1 none 1/2 brhs k branch if half carry flag set if (h = 1) then pc pc + k + 1 none 1/2 brhc k branch if half carry flag cleared if (h = 0) then pc pc + k + 1 none 1/2 brts k branch if t flag set if (t = 1) then pc pc + k + 1 none 1/2 brtc k branch if t flag cleared if (t = 0) then pc pc + k + 1 none 1/2 brvs k branch if overflow flag is set if (v = 1) then pc pc + k + 1 none 1/2 brvc k branch if overflow flag is cleared if (v = 0) then pc pc + k + 1 none 1/2 brie k branch if interrupt enabled if ( i = 1) then pc pc + k + 1 none 1/2 brid k branch if interrupt disabled if ( i = 0) then pc pc + k + 1 none 1/2 bit and bit-test instructions sbi p,b set bit in i/o register i/o(p,b) 1none2 cbi p,b clear bit in i/o register i/o(p,b) 0none2 lsl rd logical shift left rd(n+1) rd(n), rd(0) 0 z,c,n,v 1 lsr rd logical shift right rd(n) rd(n+1), rd(7) 0 z,c,n,v 1 rol rd rotate left through carry rd(0) c,rd(n+1) rd(n),c rd(7) z,c,n,v 1 214 2543l?avr?08/10 attiny2313 ror rd rotate right through carry rd(7) c,rd(n) rd(n+1),c rd(0) z,c,n,v 1 asr rd arithmetic shift right rd(n) rd(n+1), n=0..6 z,c,n,v 1 swap rd swap nibbles rd(3..0) rd(7..4),rd(7..4) rd(3..0) none 1 bset s flag set sreg(s) 1 sreg(s) 1 bclr s flag clear sreg(s) 0 sreg(s) 1 bst rr, b bit store from register to t t rr(b) t 1 bld rd, b bit load from t to register rd(b) tnone1 sec set carry c 1c1 clc clear carry c 0 c 1 sen set negative flag n 1n1 cln clear negative flag n 0 n 1 sez set zero flag z 1z1 clz clear zero flag z 0 z 1 sei global interrupt enable i 1i1 cli global interrupt disable i 0 i 1 ses set signed test flag s 1s1 cls clear signed test flag s 0 s 1 sev set twos complement overflow. v 1v1 clv clear twos complement overflow v 0 v 1 set set t in sreg t 1t1 clt clear t in sreg t 0 t 1 seh set half carry flag in sreg h 1h1 clh clear half carry flag in sreg h 0 h 1 data transfer instructions mov rd, rr move between registers rd rr none 1 movw rd, rr copy register word rd+1:rd rr+1:rr none 1 ldi rd, k load immediate rd knone1 ld rd, x load indirect rd (x) none 2 ld rd, x+ load indirect and post-inc. rd (x), x x + 1 none 2 ld rd, - x load indirect and pre-dec. x x - 1, rd (x) none 2 ld rd, y load indirect rd (y) none 2 ld rd, y+ load indirect and post-inc. rd (y), y y + 1 none 2 ld rd, - y load indirect and pre-dec. y y - 1, rd (y) none 2 ldd rd,y+q load indirect with displacement rd (y + q) none 2 ld rd, z load indirect rd (z) none 2 ld rd, z+ load indirect and post-inc. rd (z), z z+1 none 2 ld rd, -z load indirect and pre-dec. z z - 1, rd (z) none 2 ldd rd, z+q load indirect with displacement rd (z + q) none 2 lds rd, k load direct from sram rd (k) none 2 st x, rr store indirect (x) rr none 2 st x+, rr store indirect and post-inc. (x) rr, x x + 1 none 2 st - x, rr store indirect and pre-dec. x x - 1, (x) rr none 2 st y, rr store indirect (y) rr none 2 st y+, rr store indirect and post-inc. (y) rr, y y + 1 none 2 st - y, rr store indirect and pre-dec. y y - 1, (y) rr none 2 std y+q,rr store indirect with displacement (y + q) rr none 2 st z, rr store indirect (z) rr none 2 st z+, rr store indirect and post-inc. (z) rr, z z + 1 none 2 st -z, rr store indirect and pre-dec. z z - 1, (z) rr none 2 std z+q,rr store indirect with displacement (z + q) rr none 2 sts k, rr store direct to sram (k) rr none 2 lpm load program memory r0 (z) none 3 lpm rd, z load program memory rd (z) none 3 lpm rd, z+ load program memory and post-inc rd (z), z z+1 none 3 spm store program memory (z) r1:r0 none - in rd, p in port rd pnone1 out p, rr out port p rr none 1 push rr push register on stack stack rr none 2 pop rd pop register from stack rd stack none 2 mcu control instructions nop no operation none 1 sleep sleep (see specific descr. for sleep function) none 1 wdr watchdog reset (see specific descr. for wdr/timer) none 1 break break for on-chip debug only none n/a mnemonics operands description operation flags #clocks 215 2543l?avr?08/10 attiny2313 ordering information notes: 1. these devices can also be supplied in wafer form. please contact your local atmel sales office for detailed ordering in forma- tion and minimum quantities. 2. pb-free packaging alternative, complies to the european directive for restriction of hazardous substances (rohs direc- tive). also halide free and fully green. 3. for speed vs. v cc, see figure 82 on page 180 and figure 83 on page 180 . 4. code indicators: ? u: matte tin ? r: tape & reel speed (mhz) (3) power supply (v) ordering code (4) package (2) operation range 10 1.8 - 5.5 attiny2313v-10pu attiny2313v-10su attiny2313v-10sur attiny2313v-10mu ATTINY2313V-10MUR 20p3 20s 20s 20m1 20m1 industrial (-40 c to +85 c) (1) 20 2.7 - 5.5 attiny2313-20pu attiny2313-20su attiny2313-20sur attiny2313-20mu attiny2313-20mur 20p3 20s 20s 20m1 20m1 industrial (-40 c to +85 c) (1) package type 20p3 20-lead, 0.300" wide, plastic dual inline package (pdip) 20s 20-lead, 0.300" wide, plastic gull wing small outline package (soic) 20m1 20-pad, 4 x 4 x 0.8 mm body, quad flat no-lead/micro lead frame package (mlf) 216 2543l?avr?08/10 attiny2313 packaging information 20p3 2325 orchard parkway san jose, ca 95131 title drawing no. r rev. 20p3 , 20-lead (0.300"/7.62 mm wide) plastic dual inline package (pdip) c 20p3 1/12/04 pin 1 e1 a1 b e b1 c l seating plane a d e eb ec common dimensions (unit of measure = mm) symbol min nom max note a ? ? 5.334 a1 0.381 ? ? d 25.493 ? 25.984 note 2 e 7.620 ? 8.255 e1 6.096 ? 7.112 note 2 b 0.356 ? 0.559 b1 1.270 ? 1.551 l 2.921 ? 3.810 c 0.203 ? 0.356 eb ? ? 10.922 ec 0.000 ? 1.524 e 2.540 typ notes: 1. this package conforms to jedec reference ms-001, variation ad. 2. dimensions d and e1 do not include mold flash or protrusion. mold flash or protrusion shall not exceed 0.25 mm (0.010"). 217 2543l?avr?08/10 attiny2313 20s 218 2543l?avr?08/10 attiny2313 20m1 2325 orchard parkway san jose, ca 95131 title drawing no. r rev. 20m1 , 20-pad, 4 x 4 x 0.8 mm body, lead pitch 0.50 mm, a 20m1 10/27/04 2.6 mm exposed pad, micro lead frame package (mlf) a 0.70 0.75 0.80 a1 ? 0.01 0.05 a2 0.20 ref b 0.18 0.23 0.30 d 4.00 bsc d2 2.45 2.60 2.75 e 4.00 bsc e2 2.45 2.60 2.75 e 0.50 bsc l 0.35 0.40 0.55 side view pin 1 id pin #1 notch (0.20 r) bottom view top view note: reference jedec standard mo-220, fig . 1 (saw singulation) wggd-5. common dimensions (unit of measure = mm) symbol min nom max note d e e a2 a1 a d2 e2 0.08 c l 1 2 3 b 1 2 3 219 2543l?avr?08/10 attiny2313 errata the revision in this section refers to the revision of the attiny2313 device. attiny2313 rev c no known errata attiny2313 rev b ? wrong values read after erase only operation ? parallel programm ing does not work ? watchdog timer interrupt disabled ? eeprom can not be written below 1.9 volts 1. wrong values read after erase only operation at supply voltages below 2.7 v, an eeprom location that is er ased by the er ase only oper- ation may read as programmed (0x00). problem fix/workaround if it is necessary to read an eeprom location after erase only, use an atomic write opera- tion with 0xff as data in order to erase a loca tion. in any case, the write only operation can be used as intended. thus no special consider ations are needed as long as the erased loca- tion is not read before it is programmed. 2. parallel programming does not work parallel programming is not functioning correct ly. because of this, reprogramming of the device is impossible if one of the following modes are selected: ? in-system programming disabled (spien unprogrammed) ? reset disabled (rstdisbl programmed) problem fix/workaround serial programming is still working correctly . by avoiding the two modes above, the device can be reprogrammed serially. 3. watchdog timer interrupt disabled if the watchdog timer interrup t flag is not cleared before a new timeout occurs, the watchdog will be disabled, and the interrupt flag will automatically be cleared . this is only applicable in interrupt only mode. if the watchdog is configur ed to reset the device in the watchdog time- out following an interrupt, the device works correctly. problem fix / workaround make sure there is enough time to always service the first timeout event before a new watchdog timeout occurs. this is done by selecting a long enough time-out period. 4. eeprom can not be written below 1.9 volts writing the eeprom at v cc below 1.9 volts might fail. problem fix / workaround do not write the eeprom when v cc is below 1.9 volts. attiny2313 rev a revision a has not been sampled. 220 2543l?avr?08/10 attiny2313 datasheet revision history please note that the referring page numbers in this section refer to the complete document. rev. 2543l - 8/10 added tape and reel part numbers in ?ordering information? on page 215 . removed text ?not recommended for new design? from cover page. fixed literature number mismatch in datasheet revision history. rev. 2543k - 03/10 rev. 2543j - 11/09 changes from rev. 2543h-02/05 to rev. 2543i-04/06 changes from rev. 2543g-10/04 to rev. 2543h-02/05 1. added device rev c ?no known errata? in ?errata? on page 219 . 1. updated template 2. changed device status to ?not recommended for new designs.? 3. updated ?stack pointer? on page 11 . 4. updated table ?sleep mode select? on page 30 . 5. updated ?calibration byte? on page 160 (to one byte of calibration data) 1. updated typos. 2. updated figure 1 on page 2 . 3 added ?resources? on page 6 . 4. updated ?default clock source? on page 23 . 5. updated ?128 khz internal oscillator? on page 28 . 6. updated ?power management and sleep modes? on page 30 7. updated table 3 on page 23 , table 13 on page 30 , table 14 on page 31 , table 19 on page 42 , table 31 on page 60 , table 79 on page 176 . 8. updated ?external interrupts? on page 59 . 9. updated ?bit 7..0 ? pcint7..0: pin cha nge enable mask 7..0? on page 61 . 10. updated ?bit 6 ? acbg: analog comparator bandgap select? on page 149 . 11. updated ?calibration byte? on page 160 . 12. updated ?dc characteristics? on page 177 . 13. updated ?register summary? on page 211 . 14. updated ?ordering information? on page 215 . 15. changed occurences of ocna to ocfna, ocnb to ocfnb and oc1x to ocf1x. 1. updated table 6 on page 25 , table 15 on page 34 , table 68 on page 160 and table 80 on page 179 . 2. changed cksel default value in ?default clock source? on page 23 to 8 mhz. 221 2543l?avr?08/10 attiny2313 changes from rev. 2543f-08/04 to rev. 2543g-10/04 changes from rev. 2543e-04/04 to rev. 2543f-08/04 changes from rev. 2543d-03/04 to rev. 2543e-04/04 changes from rev. 2543c-12/03 to rev. 2543d-03/04 3. updated ?programming the flash? on page 165 , ?programming the eeprom? on page 167 and ?enter programming mode? on page 163 . 4. updated ?dc characteristics? on page 177 . 5. mlf option updated to ?quad flat no-lead/micro lead frame (qfn/mlf)? 1. updated ?features? on page 1 . 2. updated ?pinout attiny2313? on page 2 . 3. updated ?ordering information? on page 215 . 4. updated ?packaging information? on page 216 . 5. updated ?errata? on page 219 . 1. updated ?features? on page 1 . 2. updated ?alternate functions of port b? on page 53 . 3. updated ?calibration byte? on page 160 . 4. moved table 69 on page 160 and table 70 on page 160 to ?page size? on page 160 . 5. updated ?enter programming mode? on page 163 . 6. updated ?serial programming algorithm? on page 173 . 7. updated table 78 on page 174 . 8. updated ?dc characteristics? on page 177 . 9. updated ?attiny2313 typical characteristics? on page 181 . 10. changed occurences of pcint15 to pcint7, eemwe to eempe and eewe to eepe in the document. 1. speed grades changed - 12mhz to 10mhz - 24mhz to 20mhz 2. updated figure 1 on page 2 . 3. updated ?ordering information? on page 215 . 4. updated ?maximum speed vs. vcc? on page 180 . 5. updated ?attiny2313 typical characteristics? on page 181 . 1. updated table 2 on page 23 . 2. replaced ?watchdog timer? on page 39 . 3. added ?maximum speed vs. vcc? on page 180 . 4. ?serial programming algorithm? on page 173 updated. 5. changed ma to a in preliminary figure 136 on page 207 . 6. ?ordering information? on page 215 updated. mlf package option removed 222 2543l?avr?08/10 attiny2313 changes from rev. 2543b-09/03 to rev. 2543c-12/03 changes from rev. 2543a-09/03 to rev. 2543b-09/03 7. package drawing ?20p3? on page 216 updated. 8. updated c-code examples. 9. renamed instances of spmen to selfprgen, self programming enable. 1. updated ?calibrated internal rc oscillator? on page 25 . 1. fixed typo from uart to usart and updated speed grades and power consumption estimates in ?features? on page 1 . 2. updated ?pin configurations? on page 2 . 3. updated table 15 on page 34 and table 80 on page 179 . 4. updated item 5 in ?serial programming algorithm? on page 173 . 5. updated ?electrical characteristics? on page 177 . 6. updated figure 82 on page 180 and added figure 83 on page 180 . 7. changed sfior to gtccr in ?register summary? on page 211 . 8. updated ?ordering information? on page 215 . 9. added new errata in ?errata? on page 219 . i 2543l?avr?08/10 attiny2313 table of contents features 1 pin configurations 2 general information 6 resources 6 code examples 6 disclaimer 6 avr cpu core 7 introduction 7 architectural overview 7 alu ? arithmetic logic unit 8 status register 8 general purpose register file 9 instruction execution timing 11 reset and interrupt handling 12 avr attiny2313 memories 14 in-system reprogrammable flash program memory 14 eeprom data memory 16 i/o memory 20 system clock and clock options 22 clock systems and their distribution 22 clock sources 23 default clock source 23 crystal oscillator 23 calibrated internal rc oscillator 25 system clock prescalar 28 power management and sleep modes 30 idle mode 30 power-down mode 31 standby mode 31 minimizing power consumption 31 system control and reset 33 interrupts 44 interrupt vectors in attiny2313 44 i/o-ports 46 introduction 46 ii 2543l?avr?08/10 attiny2313 ports as genera l digital i/o 47 alternate port functions 51 external interrupts 59 pin change interrupt timing 59 8-bit timer/counter0 with pwm 62 overview 62 timer/counter clock sources 63 counter unit 63 output compare unit 64 compare match output unit 65 modes of operation 66 timer/counter timing diagrams 71 timer/counter0 and time r/counter1 prescalers 80 16-bit timer/counter1 82 overview 82 accessing 16-bit registers 84 counter unit 88 input capture unit 89 output compare units 90 modes of operation 94 usart 111 overview 111 clock generation 112 frame formats 115 usart initialization 116 asynchronous data reception 124 universal serial interface ? usi 138 overview 138 functional descriptions 139 alternative usi usage 144 usi register descriptions 144 analog comparator 149 debugwire on-chip debug system 151 features 151 overview 151 physical interface 151 software break points 152 limitations of debugwire 152 iii 2543l?avr?08/10 attiny2313 debugwire related register in i/o memory 152 self-programming the flash 153 memory programming 158 program and data memory lock bits 158 signature bytes 160 calibration byte 160 page size 160 parallel programming parameters, pin mapping, and commands 161 serial programming pin mapping 163 parallel programming 163 serial downloading 172 external clock drive 179 attiny2313 typical characteristics 181 errata 219 attiny2313 rev c 219 attiny2313 rev b 219 attiny2313 rev a 219 datasheet revision history 220 rev. 2543l - 8/10 220 rev. 2543k - 03/10 220 rev. 2543j - 11/09 220 changes from rev. 2543h-02/05 to rev. 2543i-04/06 220 changes from rev. 2543g-10/04 to rev. 2543h-02/05 220 changes from rev. 2543f-08/04 to rev. 2543g-10/04 221 changes from rev. 2543e-04/04 to rev. 2543f-08/04 221 changes from rev. 2543d-03/04 to rev. 2543e-04/04 221 changes from rev. 2543c-12/03 to rev. 2543d-03/04 221 changes from rev. 2543b-09/03 to rev. 2543c-12/03 222 changes from rev. 2543a-09/03 to rev. 2543b-09/03 222 2543l?avr?08/10 headquarters international atmel corporation 2325 orchard parkway san jose, ca 95131 usa tel: 1(408) 441-0311 fax: 1(408) 487-2600 atmel asia unit 1-5 & 16, 19/f bea tower, millennium city 5 418 kwun tong road kwun tong, kowloon hong kong tel: (852) 2245-6100 fax: (852) 2722-1369 atmel europe le krebs 8, rue jean-pierre timbaud bp 309 78054 saint-quentin-en- yvelines cedex france tel: (33) 1-30-60-70-00 fax: (33) 1-30-60-71-11 atmel japan 9f, tonetsu shinkawa bldg. 1-24-8 shinkawa chuo-ku, tokyo 104-0033 japan tel: (81) 3-3523-3551 fax: (81) 3-3523-7581 product contact web site www.atmel.com technical support avr@atmel.com sales contact www.atmel.com/contacts literature requests www.atmel.com/literature disclaimer: the information in this document is provided in connection wi th atmel products. no license, expr ess or implied, by estoppel or otherwise, to any intellectual property right is granted by this document or in connection with the sale of atmel products. except as set forth in atmel?s terms and condi- tions of sale located on atmel?s web site, atmel assumes no li ability whatsoever and disclaims any express, implied or statutor y warranty relating to its products including , but not limited to, the implied warranty of merchantability, fitness for a particu lar purpose, or non-infringement. in no event shall atmel be liable for any direct, indire ct, consequential, punitive, special or i nciden- tal damages (including, without li mitation, damages for loss of profits, business interruption, or loss of information) arising out of the use or inability to use this document, even if atmel has been advised of the possibility of such damages. atmel makes no representations or warranties with respect to the accuracy or comp leteness of the contents of th is document and reserves the rig ht to make changes to specifications and product descriptions at any time without notice. atmel does not make any commitment to update the information contained her ein. unless specifically provided otherwise, atmel products are not suitable for, and shall not be used in, automotive applications. atmel?s products are not int ended, authorized, or warranted for use as components in applications intended to support or sustain life. ? 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