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exar corporation, 48720 kato road, fremont, ca 94538 (510) 668-7000 fax (510) 668-7017 rev. 1.20 xr16c850 uart with 128-byte fifos fifo counters and half-duplex control june 1999-1 plcc package part number pins package operating temperature xr16c850ip 40 pdip -40 c to + 85 c xr16c850ij 44 plcc -40 c to + 85 c xr16c850im 48 tqfp -40 c to + 85 c xr16c850iq 52 qfp -40 c to + 85 c 6 5 4 3 2 1 44 43 42 41 40 7 8 9 10 11 12 13 14 15 16 17 39 38 37 36 35 34 33 32 31 30 29 18 19 20 21 22 23 24 25 26 27 28 d5 d6 d7 rclk rx n.c. tx cs0 cs1 -cs2 -baudout reset -op1 -dtr -rts -op2 n.c. int -rxrdy a0 a1 a2 d4 d3 d2 d1 d0 n.c. vcc -ri -cd -dsr -cts xtal1 xtal2 -iow iow gnd n.c. -ior ior -ddis -txrdy -as xr16c850cj "std" mode connection 6 5 4 3 2 1 44 43 42 41 40 7 8 9 10 11 12 13 14 15 16 17 39 38 37 36 35 34 33 32 31 30 29 18 19 20 21 22 23 24 25 26 27 28 d5 d6 d7 s2 rx a4 tx a5 a6 a7 -lpt1 reset -op1 -dtr -rts s3 gnd irqa irqb a0 a1 a2 d4 d3 d2 d1 d0 a9 vcc -ri -cd -dsr -cts xtal1 xtal2 -iow a8 gnd s1 -ior a3 -lpt2 irqc -aen xr16c850cj "pc" mode connection general description the xr16c850 *1 (850) is a universal asynchronous receiver and transmitter (uart) and is pin compatible with the st16c550,st16c650a, and tis tl16c750 uart. the 850 is an enhanced uart with 128 byte fifos, automatic hardware/software flow control, and data rates up to 1.5mbps. it includes transmit/receive fifo counters to increase data loading and unloading throughput. onboard status registers provide error indi- cations and operational status. modem interface con- trol is included and can be optionally configured to operate with the infrared (irda) encoder/decoder. inter- nal loopback allows onboard diagnostics. the 850 is available in 40-pin pdip, 44-pin plcc, 48-pin tqfp, and 52-pin qfp packages. the 44, 48, and 52 pin versions provide both the standard (std) mode or pc mode. the std mode is compatible with the st16c450, st16c550, st16c650a and tl16c750 while the pc mode supports standard pc com port connections. the 40 pdip pin package does not offer the pc mode. features pin to pin compatible to st16c550, st16c650a and tl16c750 transmit/receive fifo counters 128 bytes of transmit/receive fifo rs-485 half duplex direction control automatic software/hardware flow control programmable, selectable transmit/receive trigger levels infrared transmitter and receiver encoder/decoder up to 1.5mbps data rate sleep mode (100 m a standby) small 7x7mm tqfp +5 or 3.3 volts operation windows 2 drivers available ordering information part number pins package operating temperature xr16c850cp 40 pdip 0 c to + 70 c xr16c850cj 44 plcc 0 c to + 70 c xr16c850cm 48 tqfp 0 c to + 70 c XR16C850CQ 52 qfp 0 c to + 70 c note *1: covered by u.s. patent # 5,649,122 and patent pending. note *2: windows is a trademark of microsoft corporation.
xr16c850 2 rev. 1.20 48 47 46 45 44 43 42 41 40 39 38 37 1 2 3 4 5 6 7 8 9 10 11 12 36 35 34 33 32 31 30 29 28 27 26 25 13 14 15 16 17 18 19 20 21 22 23 24 d11 d5 d6 d7 s2 / rclk a4 rx tx a5 / cs0 a6 / cs1 a7 / -cs2 -lpt1 / -baudout clksel xtal1 xtal2 -iow a8 / iow gnd -ior a3 / ior s1 d12/-lpt2 / -ddis irqc / -txrdy -aen / -as sel reset -op1/rs485 -dtr -rts -op2 / s3 int / irqa -rxrdy / irqb a0 a1 a2 bus 8/16 d10 d4 d3 d2 d1 d0 vcc -ri -cd -dsr -cts a9 xr16c850cm figure 1. package description, 16c850 52 51 50 49 48 47 46 45 44 43 42 41 40 1 2 3 4 5 6 7 8 9 10 11 12 13 39 38 37 36 35 34 33 32 31 30 29 28 27 14 15 16 17 18 19 20 21 22 23 24 25 26 d11 d5 d6 d7 s2 / rclk a4 rx tx a5 / cs0 a6 / cs1 a7 / -cs2 -lpt1 / -baudout tc clksel xtal1 xtal2 -iow a8 / iow gnd -dma -ior a3 / ior s1 d12/-lpt2 /- ddis irqc / -txrdy -aen /- as sel reset -op1/rs485 -dtr -rts -op2 / s3 int / irqa -rxrdy*/ irqb/drq a0 a1 a2 bus 8/16 clk 8/16 d10 d4 d3 d2 d1 d0 -dack vcc -ri -cd -dsr -cts a9 XR16C850CQ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 d0 d1 d2 d3 d4 d5 d6 d7 rclk rx tx cs0 cs1 -cs2 -baudout xtal1 xtal2 -iow iow gnd vcc -ri -cd -dsr -cts reset -op1 -dtr -rts -op2 int -rxrdy a0 a1 a2 -as -txrdy -ddis ior -ior xr16c850cp
xr16c850 3 rev. 1.20 d0-d7 -ior,ior -iow,iow reset a0-a2 -as cs0,cs1 -cs2 int -rxrdy -txrdy -dtr,-rts -op1/rs485 -op2 -cts -ri -cd -dsr tx rx data bus & control logic register select logic modem control logic interrupt control logic transmit fifo registers flow control logic transmit shift register receive fifo registers flow control logic receive shift register inter connect bus lines & control signals clock & baud rate generator xtal1 rclk xtal2 -baudout -ddis ir encoder ir decoder figure 2. block diagram (standard mode)
xr16c850 4 rev. 1.20 d0-d7 -ior -iow a0-a9 -aen s1, s2,s3 irqa irqb irqc data bus & control logic register select logic interrupt control logic decode logic -lpt1 -lpt2 -dtr,-rts -cts -ri -cd -dsr tx rx modem control logic transmit fifo registers flow control logic transmit shift register receive fifo registers flow control logic receive shift register inter connect bus lines & control signals clock & baud rate generator xtal1 xtal2 ir encoder ir decoder sel gnd figure 3. block diagram (pc mode)
xr16c850 5 rev. 1.20 a0 28 31 28 31 i address-0 select bit - internal registers address selection in pc and std modes. a1 27 30 27 30 i address-1 select bit internal registers address selection in pc and std modes a2 26 29 26 29 i address-2 select bit internal registers address selection in pc and std modes a3 / ior 22 25 20 22 i address-3 select bit or input/output read (dual function) - when the pc mode is selected, this pin is used as 4th address line to decode the com1-4 and lpt ports. during std mode operation this pin is used as read strobe. its function is the same as -ior (see -ior), except it is active high. either an active -ior or ior is required to transfer data from 850 to cpu during a read operation. connect this pin to gnd when Cior is used. a4 - 12 6 6 i address-4 select bit (internal pull-up) - when the pc mode is selected, this pin is used as 5th address line to decode the com1-4 and lpt ports. this pin has no function in the std mode. a5 / cs0 12 14 9 9 i address-5 select bit or chip select-0 (dual function) - when the pc mode is selected, this pin is used as 6th address line to decode the com1-4 and lpt ports. during std mode a logical 1 on this pin provides the chip select 0 function. connect this pin to vcc when cs1 or Ccs2 is used. a6 / cs1 13 15 10 10 i address-6 select bit or chip select-1 (dual function) - when the pc mode is selected, this pin is used as 7th address line to decode the com1-4 and lpt ports. during std mode a logical 1 on this pin provides the chip select 1 function. connect this pin to vcc when cs0 or Ccs2 is used. a7 / -cs2 14 16 11 7 i address-7 select bit or chip select -2 (dual func- tion) - when the pc mode is selected, this pin is used as 8th address line to decode the com1-4 and lpt ports. during std mode a logical 1 on this pin provides the chip select 2 function. connect this pin symbol pin signal pin description 40 44 48 52 type symbol description
xr16c850 6 rev. 1.20 to gnd when cs0 or cs1 is used. a8 / iow 19 21 17 18 i address-8 select bit or input/output write (dual function) - when the pc mode is selected, this pin is used as 9th address line to decode the com1-4 and lpt ports. during std mode, a logic 1 transition creates a write strobe. its function is the same as - iow (see -iow), but it acts as an active high input signal. either -iow or iow is required to transfer data from the cpu to 850 during a write operation. connect this pin to gnd when Ciow is used. a9 - 1 37 40 i address-9 select bit (internal pull-up) - when the pc mode is selected, this pin is used as 10th address line to decode the com1-4 and lpt ports. this pin has no function in the std mode. -aen / -as 25 28 24 26 i address enable or address strobe (dual function) - . during pc mode operation, valid com1-4 ports are decoded when -aen transitions to a logic 0. during the std mode a logic 0 transition on -as latches the state of the chip selects and the register select bits, a0-a2. this input is used when address and chip selects are not stable for the duration of a read or write operation, i.e., a microprocessor that needs to demultiplex the address and data bits. if not re- quired, the -as input can be permanently tied to gnd (it is edge triggered). -baudout (see lpt-1) d0-d7 1-8 2-9 43-47 47-51 2-4 2-4 i/o data bus (bi-directional) - these pins are the eight bit, three state data bus for transferring information to or from the controlling cpu. d0 is the least significant bit and the first data bit in a transmit or receive serial data stream. d10, d11, - - 48,1 52,1 d12 22 24 o high order data bus. when 16 bit data bus (bus8/ 16 = logic zero) is selected, received data errors (parity, framing, break) can be read along with its data byte on these pins. d10 is parity error bit, d11 symbol pin signal pin description 40 44 48 52 type symbol description
xr16c850 7 rev. 1.20 is framing error bit and d12 is the break bit. bus8/16 - - 25 28 i 8 or 16 bit bus select (internal pull-up). for normal 8 bit data bus operation this pin should be connected to vcc. connect this pin to gnd for 16 bit data bus operation where rx data errors (parity, framing and break) are presented on the data bus as d10, d11 and d12 along with the data byte. clk8/16 - - - 27 i transmit / receive data sampling clock rate (inter- nal pull-up). for normal operation this pin should be connected to vcc for 16x sampling clock (stan- dard). connect to gnd for 8x sampling to double the data rates. drq - - - 32 o receive dma request. a receive ready request is generated by bringing a rxdrq line to a high level. drq line is held high until the corresponding dma acknowledge (-dack) line goes low. -dack - - - 46 i dma acknowledge bit (internal pull-up). dma cycle will start processing when cpu/host sets this input to low. connect this pin to vcc when not used. -ddis (see lpt-2) gnd 20 22 18 19 pwr signal and power ground. int (see irqa) -ior 21 24 19 21 i input/output read (active low strobe). a logic 0 on this pin transfers the contents of the 850 data bus to the cpu. connect this pin to vcc when ior is used. -iow 18 20 16 17 i input/output write (active low strobe) - a logic 0 on this pin transfers the contents of the cpu data bus to the addressed internal register. connect this pin to vcc when iow is used. irqa / int 30 33 30 33 o interrupt request a or interrupt (three state, open source, active high) - during pc mode of operation, this pin functions as irqa. irqa is enabled when symbol pin signal pin description 40 44 48 52 type symbol description
xr16c850 8 rev. 1.20 mcr bit-3 is set to a logic 1, interrupts are enabled in the interrupt enable register (ier), and when an interrupt condition exists. interrupt conditions in- clude: receiver errors, available receiver buffer data, transmit buffer empty, or when a modem status flag is detected. during std mode operation the three state mode is disabled and this pin functions as int (interrupt request). irqb/-rxrdy 29 32 29 32 o interrupt request b or receive ready (three state, dual function) -. during pc mode operation, a logic 1 indicates an interrupt irqb (see further descrip- tion under the irqa). during the std mode a logic 0 indicates receive data ready status, i.e. the rhr is full or the fifo has one or more rx characters available for unloading. this pin goes to a logic 0 when the fifo/rhr is full or when there are more characters available in either the fifo or rhr. irqc/-txrdy 24 27 23 25 o interrupt request c or transmit ready (three state, dual function) - during pc mode operation, a logic 1 on this pin indicates an interrupt irqc (see further description under the irqa). during the std mode buffer ready status is indicated by a logic 0, i.e., at least one location is empty and available in the fifo or thr. this pin goes to a logic 1 when there are no more empty locations in the fifo or thr. -lpt-1 / -baudout 15 17 12 12 o baud rate generator output or line printer port-1 decode logic output. (dual function, active low) - when the pc mode is selected, the baud rate generator clock output is internally connected to the rclk input. this pin then functions as the lpt-1 printer port decode logic output, see table 2. during std mode operation, this pin provides the 16x clock of the selected data rate from the baud rate genera- tor. the rclk pin must be connected externally to -baudout when the receiver is operating at the same data rate. -lpt2/-ddis 23 26 22 24 o drive disable or line printer port-2 decode logic output (dual function, active low) - when the pc symbol pin signal pin description 40 44 48 52 type symbol description
xr16c850 9 rev. 1.20 symbol pin signal pin description 40 44 48 52 type symbol description mode is selected, this pin functions as the lpt-2 printer port decode logic output, see table 2. during the std mode this pin goes to a logic 0 when the external cpu is reading data from the 850. this signal can be used to disable external transceivers or other logic functions. also, this pin may be d12 signal when bus16 is selected in 48 and 52 pin packages. -op1/rs485 34 38 34 37 o output-1(user defined) or rs-485 direction control signal. general purpose output during normal opera- tion - see bit-2 of modem control register (mcr bit- 2). rs-485 direction control can be selected when fctr bit-3 is set to 1. during data transmit cycle, -op1/rs485 pin is low. -op2 (see s3) rclk (see s2) reset 35 39 35 38 i reset. (active high) - a logic 1 on this pin will reset the internal registers and all the outputs. during reset, the uart transmitter output and the receiver input are disabled, the data bus is still controlled by cs0, cs1, -cs2 and -ior. (see xr16c850 external reset conditions for initialization details.) -rxrdy (see irqb) s1 - 23 21 23 i port select-1 (internal pull-up) - when pc mode is selected, s1 is used in conjunction with s2, s3 and a3-a9 to select one of the pc com port addresses (see table 2 internal address decode function) this pin has no function in the std mode. s2 / rclk 9 10 5 5 i port select-2 or receive clock input (dual function input with internal pull-up) - when pc mode is selected, the rclk input is connected internally to -baudout and s2 is used in conjunction with s1, s3 and a3-a9 to select one of the pc com port addresses. during std mode operation, this pin is used as external 16x clock input to the receiver section, normally its connected to -baudout.
xr16c850 10 rev. 1.20 symbol pin signal pin description 40 44 48 52 type symbol description s3 / -op2 31 35 31 34 i/o select-3 or user defined output-2 (dual function with internal pull-up) - when pc mode is selected, s3 is used in conjunction with s1, s2 and a3-a9 to select one of the pc com port addresses. in the std mode this pin provides the user a general purpose output. see bit-3 modem control register (mcr bit-3). sel - 34 36 39 i select mode (internal pull-up) - the pc mode is selected by a logic 0 (gnd) on this pin and std mode is selected when this pin is a logic 1 (left open or tied to vcc). this pin is not available on the 40 pin pdip packages which operate in the std mode only. tc - - - 13 i terminal count bit (internal pull-up). a high pulse indicates terminal count for any dma channel is reached. connect this pin to gnd when not used. -txrdy (see irqc) vcc 40 44 42 45 pwr power supply input. xtal1 16 18 14 15 i crystal or external clock input - functions as a crystal input or as an external clock input. a crystal can be connected between this pin and xtal2 to form an internal oscillator circuit. an external 1 m w resistor is required between the xtal1 and xtal2 pins (see figure 9). alternatively, an external clock can be connected to this pin to provide custom data rates (programming baud rate generator section). xtal2 17 19 15 16 o output of the crystal oscillator or buffered clock - (see also xtal1). crystal oscillator output or buff- ered clock output. -cd 38 42 40 43 i carrier detect (active low) - a logic 0 on this pin indicates that a carrier has been detected by the modem. -cts 36 40 38 41 i clear to send (active low) - a logic 0 on the -cts pin indicates the modem or data set is ready to accept transmit data from the 850. status can be tested by
xr16c850 11 rev. 1.20 symbol pin signal pin description 40 44 48 52 type symbol description reading msr bit-4. this pin only affects the transmit and receive operations when auto cts function is enabled via the enhanced feature register (efr) bit-7, for hardware flow control operation. -dsr 37 41 39 42 i data set ready (active low) - a logic 0 on this pin indicates the modem or data set is powered-on and is ready for data exchange with the uart. this pin has no effect on the uarts transmit or receive operation. -dtr 33 37 33 36 o data terminal ready (active low) - a logic 0 on this pin indicates that the 850 is powered-on and ready. this pin can be controlled via the modem control register. writing a logic 1 to mcr bit-0 will set the - dtr output to logic 0, enabling the modem. this pin will be a logic 1 after writing a logic 0 to mcr bit-0, or after a reset. this pin has no effect on the uarts transmit or receive operation. -ri 39 43 41 44 i ring indicator (active low) - a logic 0 on this pin indicates the modem has received a ringing signal from the telephone line. a logic 1 transition on this input pin will generate an interrupt. -rts 32 36 32 35 o request to send (active low) - a logic 0 on the -rts pin indicates the transmitter has data ready and waiting to send. writing a logic 1 in the modem control register (mcr bit-1) will set this pin to a logic 0 indicating data is available. after a reset this pin will be set to a logic 1. this pin only affects the transmit and receive operations when auto rts function is enabled via the enhanced feature reg- ister (efr) bit-6, for hardware flow control operation. rx / irrx 10 11 7 7 i receive data - this pin provides the serial receive data input to the 850. two user selectable interface options are available. the first option supports the standard serial interface. the second option pro- vides an infrared decoder interface, see figures 2 and 3. when using the standard modem interface, the rx input must be a logic 1 during idle (no data
xr16c850 12 rev. 1.20 or mark condition). the inactive state (no data) for the infrared decoder interface is a logic 0. mcr bit- 6 selects the standard modem or infrared interface. during the local loopback mode, the rx pin is disconnected and tx data is internally connected to the rx input, see figure 12. tx / irtx 11 13 8 8 o transmit data - this pin provides the serial transmit data from the 850. two user selectable interface options are available. the first user option supports a standard modem interface. the second option provides an infrared encoder interface, see figures 2 and 3. when using the standard serial interface, the tx signal will be a logic 1 during reset, idle (no data), or when the transmitter is disabled. the inactive state (no data) for the infrared encoder interface is a logic 0. mcr bit-6 selects the standard serial or infrared interface. during the local loopback mode, the tx pin is disconnected and tx data is internally connected to the rx input, see figure 12. clksel - - 13 14 i clock select bit (internal pull-up). - the 1x or 4x pre- scaleable clock is selected by this pin. the 1x clock is selected when clksel is a logic 1 (connected to vcc) or the 4x is selected when clksel is a logic 0 (connected to gnd). mcr bit-7 can override the state of this pin following reset or initialization (see mcr bit-7). this pin is not available on 40 and 44 pin packages which provide mcr bit-7 selection only. -dma - - - 20 i dma mode enable (internal pull-up). dma mode is enabled when this pin is connected to gnd. tc, - dack, drq functions are activated when dma mode is selected. tx and rx dma mode can then be selected by register emsr bit 2. connect this pin to vcc when dma mode is not used. symbol pin signal pin description 40 44 48 52 type symbol description
xr16c850 13 rev. 1.20 general description the xr16c850 provides serial asynchronous receive data synchronization, parallel-to-serial and serial-to- parallel data conversions for both the transmitter and receiver sections. these functions are necessary for converting the serial data stream into parallel data that is required with digital data systems. synchronization for the serial data stream is accomplished by adding start and stops bits to the transmit data to form a data character (character orientated protocol). data integ- rity is insured by attaching a parity bit to the data character. the parity bit is checked by the receiver for any transmission bit errors. the electronic circuitry to provide all these functions is fairly complex especially when manufactured on a single integrated silicon chip. the xr16c850 represents such an integration with greatly enhanced features. the 850 is fabricated with an advanced cmos process. the 850 is an upward solution that provides 128 bytes of transmit and receive fifo memory, instead of 32 bytes provided in the 16c650a, 16 bytes in the 16c550, or none in the 16c450. the 850 is designed to work with high speed modems and shared network environ- ments, that require fast data processing time. in- creased performance is realized in the 850 by the larger transmit and receive fifos. this allows the external processor to handle more networking tasks within a given time. for example, the st16c550 with a 16 byte fifo, unloads 16 bytes of receive data in 1.53 ms (this example uses a character length of 11 bits, including start/stop bits at 115.2kbps). this means the external cpu will have to service the receive fifo at 1.53 ms intervals. however with the 128 byte fifo in the 850, the data buffer will not require unloading/loading for 12.2 ms. this increases the service interval giving the external cpu additional time for other applications and reducing the overall uart interrupt servicing time. in addition, the 4 selectable levels of fifo trigger interrupt and automatic hardware/software flow control is uniquely provided for maximum data throughput perfor- mance especially when operating in a multi-channel environment. the combination of the above greatly reduces the bandwidth requirement of the external controlling cpu, increases performance, and reduces power consumption. the 850 provides a rs-485 half-duplex direction control signal, pin Cop1/rs485, to select the external trans- ceiver direction. it automatically changes the state of the output pin after the last stop-bit of the last character has been shifted out for receive state. afterward, upon loading a tx data byte it changes state of the output pin back for transmit state. the rs-485 direction control pin is not activated after reset. to activate the direction control function, user has to set efr bit-4, and fctr bit-3 to 1. this pin is normally high for receive state, low for transmit state. two data bus interfaces are available to the user. the pc mode allows direct interconnect to the pc isa bus while the std mode operates similar to the standard cpu interface available on the 16c450/550/650a. when the pc mode is selected, the external logic circuitry required for pc com port address decode and chip select is eliminated. these functions are provided internally in the 850. the 850 is capable of operation to 1.5mbps with a 24 mhz crystal or external clock input. with a crystal of 14.7464 mhz and through a software option, the user can select data rates up to 460.8kbps or 921.6kbps. the rich feature set of the 850 is available through internal registers. automatic hardware/software flow control, selectable transmit and receive fifo trigger levels, selectable tx and rx baud rates, infrared en- coder/decoder interface, modem interface controls, and a sleep mode are all standard features. in addition the 44/48/52 pin packages offer the pc mode, two additional three state interrupt lines and one selectable open source interrupt output. the open source interrupt scheme allows multiple interrupts to be combined in a wire-or operation, thus reducing the number of interrupt lines in larger systems. following a power on reset or an external reset, the 850 is software compat- ible with previous generation of uarts, 16c450, 16c550 and 16c650a.
xr16c850 14 rev. 1.20 d0 d1 d2 d3 d4 d5 d6 d7 a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 aen* ior* iow* re set address decode logic 1 3 5 7 2 4 6 8 j1 hdr2x4 3f8 2f8 3e8 2e8 d0 d1 d2 d3 d4 d5 d6 d7 -ior -iow a0 a1 a2 -cs2 re set vcc cs0 cs1 -as ior iow irq3 int 1 2 3 u2a 74ls125a -op2 rclk -baudout 1 3 2 4 j2 hdr2x2 irq4 sel functional descriptions interface options standard 16550 mode interface the 850 provides a pin compatible interface for emula- tion of the 16c550 when in the std mode. the std mode is selected by making the sel pin a logic 1 (vcc). when the sel pin is set to a logic 1, the 850 interface is the same as industry standard 16c550. figure 4 shows a typical connection to the pc isa bus. figure 4, standard mode interface
xr16c850 15 rev. 1.20 d0 d1 d2 d3 d4 d5 d6 d7 a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 aen* ior* iow* re set d0 d1 d2 d3 d4 d5 d6 d7 -ior -iow a0 a1 a2 re set a3 a4 a5 a6 a7 a8 a9 -aen 1 3 5 2 4 6 j1 hdr2x3 s1 s2 s3 irq4 irq3 irqn inta intb intc sel pc mode interface (available on 44/48/52 pin ver- sions only) the pc mode is selected by making the sel pin a logic 0 (gnd). when the pc mode is selected, the 850 eliminates the external address decode logic circuitry that is required. the pc mode is accomplished by decoding the pc isa bus address bits, a3 through a9 inside the 850. these addresses select the standard pc com ports: com-1 (3f8-3ff hex), com-2 (2f8- 2ff hex), com-3 (3e8-3ef hex), and com-4 (2e8- 2ef hex). three inputs (s1-s3) are generally exter- nally jumpered (logic 1 or logic 0) for selecting the oper ating port. the selection bits are also associated with a given pc interrupt. interrupts irqa, irqb, and irqc function as three state outputs. mcr bit-3 must be set to a logic 1 to activate these interrupts. the mapping for the com port 1-4 and their associated interrupt selec- tions, irqx are listed in table 2, below. figure 5 shows a typical connection to the pc isa bus. in addition to the com port addresses, the 850 de- codes two additional printer addresses. these address decodes select lpt-1 (printer port-1, 378-37f hex), or lpt-2 (printer port-2, 278-27f hex). these ports are intended to be compatible with pc or pc compatible computer printer ports. figure 5. pc mode interface
xr16c850 16 rev. 1.20 sel s3 s2 s1 a3-a9 com port selected irq *2 0 0 0 0 3f8-3ff com-1 irqb (irq4) 0 0 0 1 2f8-2ff com-2 irqc (irq3) 0 0 1 0 3e8-3ef com-3 irqb (irq4) 0 0 1 1 2e8-2ef com-4 irqc (irq3) 0 1 0 0 3f8-3ff com-1 irqa (irqn) 0 1 0 1 2f8-2ff com-2 irqa (irqn) 0 1 1 0 3e8-3ef com-3 irqa (irqn) 0 1 1 1 2e8-2ef com-4 irqa (irqn) 0 - - - 278-27f lpt-2 n/a 0 - - - 378-37f lpt-1 n/a table 2. pc mode internal address decode functions note *2: all interrupt outputs are inactive (three state mode) except when the selected address range is valid.
xr16c850 17 rev. 1.20 internal registers the 850 provides 15 internal registers for monitoring and control. these registers are shown in table 3 below. twelve registers are similar to those already available in the standard 16c550. these registers function as data holding registers (thr/rhr), interrupt status and con- trol registers (ier/isr), a fifo control register (fcr), line status and control registers, (lcr/lsr), modem status and control registers (mcr/msr), program- mable data rate (clock) control registers (dll/dlm), and a user assessable scratchpad register (spr). beyond the general 16c550 features and capabilities, the 850 offers an enhanced feature register set called efr, xon/xoff 1-2, trg, fctr, and emsr. register functions are more fully described in the following paragraphs. a2 a1 a0 read mode write mode general register set (thr/rhr, ier/isr, mcr/msr, lcr/lsr, spr): 0 0 0 receive holding register transmit holding register 0 0 1 interrupt enable register 0 1 0 interrupt status register fifo control register 0 1 1 line control register 1 0 0 modem control register 1 0 1 line status register 1 1 0 modem status register 1 1 1 scratchpad register scratchpad register baud rate register set (dll/dlm): note *3 0 0 0 lsb of divisor latch lsb of divisor latch 0 0 1 msb of divisor latch msb of divisor latch enhanced register set (xon/off 1-2, trg, fctr, efr, emsr): note *4 0 0 0 fifo trigger register fifo trigger counter 0 0 1 feature control register 0 1 0 enhanced feature register enhanced feature register 1 0 0 xon-1 word xon-1 word 1 0 1 xon-2 word xon-2 word 1 1 0 xoff-1 word xoff-1 word 1 1 1 xoff-2 word xoff-2 word 1 1 1 enhanced mode select register table 3. internal registers note *3: these registers are accessible only when lcr bit-7 is set to a logic 1. note *4: enhanced feature registers are accessible only when the lcr is set to bf hex.
xr16c850 18 rev. 1.20 fifo operation the 128 byte transmit and receive data fifos are enabled by the fifo control register (fcr) bit-0. with 16c550 devices, the user can only set the receive trigger level but not the transmit trigger level. the 850 provides independent trigger levels for both receiver and transmitter. to remain compatible with 16c550, the transmit interrupt trigger level is set to 16 following a reset. it should be noted that the user can set the transmit trigger levels by writing to the fcr register, but activation will not take place until efr bit-4 is set to a logic 1. the receiver fifo section includes a time-out function to ensure data is delivered to the cpu. an interrupt is generated whenever the receive holding register (rhr) has not been read following the loading of a character or the receive trigger level has not been reached. (see hardware flow control for a description of this timing). hardware flow control when automatic hardware flow control is enabled, the 850 monitors the -cts pin for a remote buffer overflow indication and controls the -rts pin for local buffer overflows. automatic hardware flow control is selected by setting bits 6 (rts) and 7 (cts) of the efr register to a logic 1. if -cts transitions from a logic 0 to a logic 1 indicating a flow control request, isr bit-5 will be set to a logic 1 (if enabled via ier bit 6-7), and the 850 will suspend tx transmissions as soon as the stop bit of the character in process is shifted out. transmission is resumed after the -cts input returns to a logic 0, indicating more data may be sent. the 850 has a new feature that provides flow control trigger hysteresis while maintains compatibility to 16c650a and 16c550. with the auto rts function enabled, an interrupt is generated when the receive fifo reaches the programmed rx trigger level. the - rts pin will not be forced to a logic 1 (rts off), until the receive fifo reaches the upper limit of the hysteresis level . the -rts pin will return to a logic 0 after the rx data buffer (fifo) is unloaded to the lower limit of the hysteresis level. under the above described conditions the 850 will continue to accept data until the receive fifo gets full. the auto rts function is initiated when the Crts output pin is asserted to logic 0 (rts on). below shows the 650a and 850 hysteresis level of n with respect to auto rts flow control levels. fctr trigger rts int -rts -rts bit-1 and 0 level hysteresis pin de-asserted asserted selection (characters) (characters) activation at (characters) (characters) 00 8 8 16 0 00 16 16 24 8 00 24 24 28 16 00 28 28 28 24 01 n +/-4 n n plus 4 n minus 4 10 n +/-6 n n plus 6 n minus 6 10 n +/-6 n n plus 6 n minus 6
xr16c850 19 rev. 1.20 software flow control when software flow control is enabled, the 850 com- pares one or two sequential receive data characters with the programmed xon or xoff-1,2 character value(s). if receive character(s) (rx) match the programmed val- ues, the 850 will halt transmission (tx) as soon as the current character(s) has completed transmission. when a match occurs, the receive ready (if enabled via xoff ier bit-5) flags will be set and the interrupt output pin (if receive interrupt is enabled) will be activated. following a suspension due to a match of the xoff characters values, the 850 will monitor the receive data stream for a match to the xon-1,2 character value(s). if a match is found, the 850 will resume operation and clear the flags (isr bit-4). reset initially sets the contents of the xon/xoff 8-bit flow control registers to a logic 0. following reset the user can write any xon/xoff value desired for software flow control. different conditions can be set to detect xon/ xoff characters and suspend/resume transmissions. when double 8-bit xon/xoff characters are selected, the 850 compares two consecutive receive characters with two software flow control 8-bit values (xon1, xon2, xoff1, xoff2) and controls tx transmissions accordingly. un- der the above described flow control mechanisms, flow control characters are not placed (stacked) in the user accessible rx data buffer or fifo. in the event that the receive buffer is overfilling and flow control needs to be executed, the 850 automatically sends an xoff message (when enabled) via the serial tx output to the remote modem. the 850 sends the xoff-1,2 characters as soon as received data passes the pro- grammed trigger level. to clear this condition, the 850 will transmit the programmed xon-1,2 characters as soon as receive data drops below the programmed trigger level. special feature software flow control a special feature is provided to detect an 8-bit character when bit-5 is set in the enhanced feature register (efr). when this character is detected, it will be placed on the user accessible data stack along with normal incoming rx data. this condition is selected in conjunc- tion with efr bits 0-3. note that software flow control should be turned off when using this special mode by setting efr bit 0-3 to a logic 0. the 850 compares each incoming receive character with xoff-2 data. if a match exists, the received data will be transferred to fifo and isr bit-4 will be set to indicate detection of special character (see figure 9). although the internal register table shows each x- register with eight bits of character information, the actual number of bits is dependent on the programmed word length. line control register (lcr) bits 0-1 defines the number of character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. the word length selected by lcr bits 0- 1 also determines the number of bits that will be used for the special character comparison. bit-0 in the x- registers corresponds with the lsb bit for the receive character. time-out interrupts three special interrupts have been added to monitor the hardware and software flow control. the interrupts are enabled by ier bits 5-7. care must be taken when handling these interrupts. following a reset the trans- mitter interrupt is enabled, the 850 will issue an interrupt to indicate that transmit holding register is empty. this interrupt must be serviced prior to continuing opera- tions. the lsr register provides the current singular highest priority interrupt only. it could be noted that cts and rts interrupts have lowest interrupt priority. a condition can exist where a higher priority interrupt may mask the lower priority cts/rts interrupt(s). only after servicing the higher pending interrupt will the lower priority cts/ rts interrupt(s) be reflected in the status register. servicing the interrupt without investigating further interrupt conditions can result in data errors. when two interrupt conditions have the same priority, it is important to service these interrupts correctly. re- ceive data ready and receive time out have the same interrupt priority (when enabled by ier bit-0). the receiver issues an interrupt after the number of charac- ters have reached the programmed trigger level. in this case the 850 fifo may hold more characters than the programmed trigger level. following the removal of a data byte, the user should recheck lsr bit-0 for additional characters. a receive time out will not occur if the receive fifo is empty. the time out counter is reset at the center of each stop bit received or each time the receive holding register (rhr) is read. the actual time out value is t ( t ime out length in bits) = 4 x p
xr16c850 20 rev. 1.20 c1 22pf c2 33pf x1 1.8432 mhz r1 50-120 r2 1m xta l 1 xta l 2 ( p rogrammed word length) + 12. to convert the time out value to a character value, the user has to consider the complete word length, including data information length, start bit, parity bit, and the size of stop bit, i.e., 1x, 1.5x, or 2x bit times. example -a: if the user programs a word length of 7, with no parity and one stop bit, the time out will be: t = 4 x 7( programmed word length) +12 = 40 bit times. the character time will be equal to 40 / 9 = 4.4 characters, or as shown in the fully worked out example: t = [(programmed word length = 7) + (stop bit = 1) + (start bit = 1) = 9]. 40 (bit times divided by 9) = 4.4 characters. example -b: if the user programs the word length = 7, with parity and one stop bit, the time out will be: t = 4 x 7(programmed word length) + 12 = 40 bit times. character time = 40 / 10 [ (programmed word length = 7) + (parity = 1) + (stop bit = 1) + (start bit = 1) = 4 characters. due to limitations involved in servicing a number of simultaneous interrupts in pcs and multi-channel sys- tems, the 850 offers shared wire-or interrupts by setting mcr bit-5 to a logic 1. when using this mode, the connection of a 200-500 ohm resistor is required be- tween the irqa/int pin and signal ground to provide an acceptable logic 0 level. the other interrupts (irqb, irqc) are inactive when using this mode. programmable baud rate generator the 850 supports high speed modem technologies that have increased input data rates by employing data compression schemes. for example a 33.6kbps mo- dem that employs data compression may require a 115.2kbps input data rate. a 128.0kbps isdn modem that supports data compression may need an input data rate of 460.8kbps. the 850 can support a standard data rate of 921.6kbps with a crystal of 14.7456mhz. a single baud rate generator is provided for the transmit- ter and receiver, allowing independent tx/rx channel control. the programmable baud rate generator is capable of accepting an input clock up to 24 mhz, as required for supporting a 1.5mbps data rate. the 850 can be configured for internal or external clock opera- tion. for internal clock oscillator operation, an industry standard microprocessor crystal (parallel resonant/ 22- 33 pf load) is connected externally between the xtal1 and xtal2 pins, with an external 500k to 1 m w resistor across it. the serial 50-120 w resistor on pin xtal2 may be deleted for high frequency crystal operation . alterna- tively, an external clock can be connected to the xtal1 pin to clock the internal baud rate generator for standard or custom rates. the generator divides the input 16x clock by any divisor from 1 to 2 16 -1. the 850 divides the basic crystal or external clock by 16. further division of this 16x clock provides two table rates to support low and high data rate applications using the same system design. the two rate tables are selectable through the internal register, mcr bit-7. setting mcr bit-7 to a logic 1 provides an additional divide by 4 whereas, setting mcr bit-7 to a logic 0 only divides by 1. (see table 4 and figure 11). the frequency of the -baudout output pin is exactly 16x (16 times) of the selected baud rate (- baudout =16 x baud rate). customized baud rates can be achieved by selecting the proper divisor values for the msb and lsb sections of baud rate generator. programming the baud rate generator registers dlm (msb) and dll (lsb) provides a user capability for selecting the desired final baud rate. the example in table 4 below, shows the two selectable baud rate tables available when using a 7.3728 mhz crystal.
xr16c850 21 rev. 1.20 divide by 1 logic x tal1 x tal2 divide by 4 logic clock oscillator logic baudrate generator logic -baudout mcr bit-7=0 mcr bit-7=1 output output user user dlm dll baud rate baud rate 16 x clock 16 x clock program program mcr mcr divisor divisor value value bit-7=1 bit-7=0 (decimal) (hex) (hex) (hex) 50 200 2304 900 09 00 75 300 1536 600 06 00 150 600 768 300 03 00 300 1200 384 180 01 80 600 2400 192 c0 00 c0 1200 4800 96 60 00 60 2400 9600 48 30 00 30 4800 19.2k 24 18 00 18 7200 28.8k 16 10 00 10 9600 38.4k 12 0c 00 0c 19.2k 76.8k 6 06 00 06 38.4k 153.6k 3 03 00 03 57.6k 230.4k 2 02 00 02 115.2k 460.8k 1 01 00 01 figure 11. baud rate generator circuitry table 4. baud rate generator programming table (7.3728 mhz clock)
xr16c850 22 rev. 1.20 dma operation the 850 fifo trigger level provides additional flexibility to the user for block transfer operation. lsr bits 5-6 provide an indication when the transmitter is empty or has an empty location(s). the user can optionally operate the transmit and receive fifos in the dma mode (fcr bit-3). when the transmit and receive fifos are enabled and the dma mode is deactivated (dma mode 0), the 850 activates the interrupt output pin for each data transmit or receive operation. when dma mode is activated (dma mode 1), the user takes the advantage of block mode operation by loading or unload- ing the fifo in a block sequence determined by the preset trigger level. in this mode, the 850 sets the interrupt output pin when characters in the transmit fifos are below the transmit trigger level, or the characters in the receive fifos are above the receive trigger level. transmit or receive dma operation is selected by emsr register bit 2. sleep mode the 850 is designed to operate with low power con- sumption. a sleep mode is included to further reduce power consumption when the chip is not being used. the operating parameters are maintained while in sleep mode. with efr bit-4 and ier bit-4 enabled (set to a logic 1), the 850 enters the sleep mode when no interrupt is pending and no activities on the modem port. if an external clock is supplied to the 850, you may want to stop it. the 850 resumes normal operation when a rx characters start bit is detected, a change of state on any of the modem input pins rx, -ri, -cts, -dsr, -cd, or transmit data is loaded into the fifo by the user. it typically takes 30us for the crystal oscillator to restart from sleep mode depending on the crystal properties. this delay must be taken into consideration during design as rx character(s) may be lost since it depends on the operating bit rate. if the sleep mode is enabled and the 850 is awakened by one of the conditions described above, it will return to the sleep mode auto- matically after the last character is transmitted or read by the user and no interrupt is pending. in any case, the chip will not enter sleep mode while an interrupt(s) is still pending and the oscillator would still be running. the 850 will stay in the sleep mode of operation until it is disabled by setting ier bit-4 to a logic 0. sleep mode enable during initialization example: write lcr with bf hex ; access to efr registers set efr bit-4 to logic 1 ; enable enhanced function bits write lcr with op. value ; set lcr with op. parameters set ier bit-4 to logic 1 ; enable sleep mode. ; it goes to sleep when: ; no pending interrupt, ; no modem port activity then enters ; sleep mode by stopping osc. for lowest sleep current the following pins should be left at logic 1 state: s1, s2, a4, a9, bus8/16, clk8/16, clksel, -dma, -dack, sel, tc and rx. loopback mode the internal loopback capability allows onboard diag- nostics. in this mode, the normal modem interface pins are disconnected and reconfigured for loopback inter- nally. msr bits 4-7 are also disconnected. however, mcr register bits 0-3 can be used for controlling loopback diagnostic testing. in this mode, op1 and op2 in the mcr register (bits 0-1) control the modem -ri and -cd inputs respectively. mcr signals -dtr and -rts (bits 0-1) are used to control the modem -cts and -dsr inputs respectively. the transmitter output (tx) and the receiver input (rx) are disconnected from their associated interface pins, and instead are connected together internally (see figure 12). the -cts, -dsr, -cd, and -ri are disconnected from their normal modem control inputs pins, and instead are connected internally to -dtr, -rts, -op1 and -op2. loopback test data is entered into the transmit holding register via the user data bus interface, d0-d7. the transmit uart serializes the data and passes the serial data to the receive uart via the internal loopback connection. the receive uart converts the serial data back into parallel data that is then made available at the user data interface, d0-d7. the user optionally compares the received data to the initial transmitted data for verifying error free operation of the uart tx/rx circuits. in this mode, the receiver, transmitter and modem control interrupts are fully operational. however, the interrupts can only be read using lower four bits of the modem control register (mcr bits 0-3) instead of the four modem status register bits 4-7. the interrupts are still controlled by the ier.
xr16c850 23 rev. 1.20 d0-d7 -ior,ior -iow,iow reset a0-a2 -as cs0,cs1 -cs2 int -rxrdy -txrdy tx rx data bus & control logic register select logic modem control logic interrupt control logic transmit fifo registers flow control logic transmit shift register receive fifo registers flow control logic receive shift register inter connect bus lines & c ontrol signals clock & baud rate generator xtal1 rclk xtal2 -baudout -ddis ir encoder ir decoder -cts -rts -dtr -dsr -ri -cd -op1 -op2 mcr bit-4=1 figure 12. internal loopback mode diagram
xr16c850 24 rev. 1.20 register functional descriptions the following table delineates the assigned bit functions for the fifteen 850 internal registers. the assigned bit functions are more fully defined in the following paragraphs. xr16c850 accessible registers a2 a1 a0 register bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 [default] note *3 general registers are accessible when lcr bit-7 is not a logic 1 or "bf" hex 0 0 0 rhr [xx] bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 0 0 0 thr [xx] bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 0 0 1 ier [00] 0/ 0/ 0/ 0/ m odem receive transmit receive -cts -rts xoff sleep status line holding holding interrupt interrupt interrupt mode inter rupt status register register interrupt 0 1 0 fcr [00] rcvr rcvr 0/tx 0/tx dma xmit rcvr fifo trigger trigger trigger trigger mode fifo fifo enable (msb) (lsb) (msb) (lsb) select reset reset 0 1 0 isr [01] 0/ 0/ 0/ 0/ int int int int fifos fifos -rts, xoff priority priority priority status enabled enabled -cts bit-2 bit-1 bit-0 0 1 1 lcr [00] divisor set set even parity stop word word latch break parity parity enable bits length length enable bit-1 bit-0 1 0 0 mcr [00] c lock 0/ 0/ loop -op2 -op1 -rts -dtr select irrt xon back enable any 1 0 1 lsr [60] 0/ trans. trans. break framing parity overrun receive fifo empty holding interrupt error error error data error empty ready 1 1 0 msr [00] -cd -ri -dsr -cts delta delta delta delta -cd -ri -dsr -cts 1 1 1 scpad [ff] bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 baud rate generator registers are accessible only when lcr bit-7 is set to logic 1. 0 0 0 dll [00] bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 0 0 1 dlm [00] bit-15 bit-14 bit-13 bit-12 bit-11 bit-10 bit-9 bit-8
xr16c850 25 rev. 1.20 a2 a1 a0 register bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 [default] note *3 enhanced registers are accessible only when lcr is set to "bf" hex. 1 0 0 xon-1[00] bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 1 0 1 xon-2[00] bit-15 bit-14 bit-13 bit-12 bit-11 bit-10 bit-9 bit-8 1 1 0 xoff-1[00] bit-7 bit-6 bit-5 bit-4 bit-3 bit-2 bit-1 bit-0 1 1 1 xoff-2[00] bit-15 bit-14 bit-13 bit-12 bit-11 bit-10 bit-9 bit-8 0 0 0 trg [00] trig/ trig/ trig/ trig/ trig trig/ trig/ trig/ fc fc fc fc fc fc fc fc 0 0 1 fctr [00] rx/tx scpad trig trig rs485 irrx -rts -rts mode swap bit-1 bit-0 auto inv. d elay delay control bit-1 bit-0 0 1 0 efr [00] auto auto special enable cont-3 cont-2 cont-1 cont-0 -cts -rts char. ier tx,rx tx,rx tx,rx tx,rx select bits 4-7, control control control control isr, fcr bits 4-5, mcr bits 5-7 1 1 1 emsr [00] not not not not not rx/tx alt. rx/tx used used used used used d m a rx/tx fifo select fifo count count note *3: the value represents the registers initialized hex value. an x signifies a 4-bit un-initialized nibble.
xr16c850 26 rev. 1.20 transmit and receive holding register the serial transmitter section consists of an 8-bit transmit hold register (thr) and transmit shift reg- ister (tsr). the status of the thr is provided in the line status register (lsr). writing to the thr transfers the contents of the data bus (d7-d0) to the thr, providing that the thr or tsr is empty. the thr empty flag in the lsr register will be set to a logic 1 when the transmitter is empty or when data is transferred to the tsr. note that a write operation can be performed when the transmit holding register empty flag is set (logic 0 = fifo full, logic 1= at least one fifo location available). the serial receive section also contains an 8-bit receive holding register, rhr. receive data is removed from the 850 and receive fifo by reading the rhr register. the receive section provides a mechanism to prevent false starts. on the falling edge of a start or false start bit, an internal receiver counter starts counting clocks at 16x clock rate. after 7 1/2 clocks the start bit time should be shifted to the center of the start bit. at this time the start bit is sampled and if it is still a logic 0 it is validated. evaluating the start bit in this manner prevents the receiver from assembling a false character. receiver status codes will be posted in the lsr. device identification the xr16c850 provides device identification and de- vice revision code to distinguish the part from others. it is suggested to read the identification and revision information from the part only during the power on initialization routine to avoid disturbing the baud rate generator. to read the identification number from the device, it is required to set the baud rate generator divisor latch to 1 (lcr bit-7 = logic 1) and set the content of the baud rate generator dll and dlm registers to 00 hex. then read the content of dlm for 10 hex for xr16c850 and the content of dll for the revision of the part. interrupt enable register (ier) the interrupt enable register (ier) masks the inter- rupts from receiver ready, transmitter empty, line status and modem status registers. these interrupts would normally be seen on the 850 int output pin. ier vs receive fifo interrupt mode operation when the receive fifo (fcr bit-0 = a logic 1) and receive interrupts (ier bit-0 = logic 1) are enabled, the receive interrupts and register status will reflect the following: a) the receive data available interrupts are issued to the external cpu when the fifo has reached the pro- grammed trigger level. it will be cleared when the fifo drops below the programmed trigger level. b) fifo status will also be reflected in the user acces- sible isr register when the fifo trigger level is reached. both the isr register status bit and the interrupt will be cleared when the fifo drops below the trigger level. c) the data ready bit (lsr bit-0) is set as soon as a character is transferred from the shift register to the receive fifo. it is reset when the fifo is empty. ier vs receive/transmit fifo polled mode opera- tion when fcr bit-0 equals a logic 1; resetting ier bits 0- 3 enables the 850 in the fifo polled mode of operation. since the receiver and transmitter have separate bits in the lsr either or both can be used in the polled mode by selecting respective transmit or receive control bit(s). a) lsr bit-0 will be a logic 1 as long as there is one byte in the receive fifo. b) lsr bit 1-4 will indicate if an overrun error occurred in the receiver. c) lsr bit-5 will indicate when the transmit fifo is empty. d) lsr bit-6 will indicate when both the transmit fifo and transmit shift register are empty. e) lsr bit-7 will indicate any data errors within the receive fifo. this bit will clear when the error byte is unloaded. ier bit-0: logic 0 = disable the receiver ready interrupt. (normal default condition)
xr16c850 27 rev. 1.20 logic 1 = enable the receiver ready interrupt. the receiver ready interrupt is cleared when lsr is read. ier bit-1: logic 0 = disable the transmitter empty interrupt. (normal default condition) logic 1 = enable the transmitter empty interrupt. the transmitter empty interrupt is cleared when isr is read. ier bit-2: logic 0 = disable the receiver line status interrupt. (normal default condition) logic 1 = enable the receiver line status interrupt. the receiver line interrupt is cleared when lsr is read. ier bit-3: logic 0 = disable the modem status register interrupt. (normal default condition) logic 1 = enable the modem status register interrupt. the modem status interrupt is cleared when msr is read. ier bit -4: logic 0 = disable sleep mode. (normal default condi- tion) logic 1 = enable sleep mode. see sleep mode section for details. ier bit-5: logic 0 = disable the software flow control, receive xoff interrupt. (normal default condition) logic 1 = enable the software flow control, receive xoff interrupt. the xoff interrupt is cleared by reading the isr register or upon receiving a xon character. also, when special character mode is enabled (efr-bit 5 =1) reading the isr register or a following received character will cleared the interrupt. see software flow control section for details. ier bit-6: logic 0 = disable the rts interrupt. (normal default condition) logic 1 = enable the rts interrupt. the 850 issues an interrupt when the rts pin transitions from a logic 0 to a logic 1 as reported in msr bit-register. the interrupt is cleared by reading the msr register. ier bit-7: logic 0 = disable the cts interrupt. (normal default condition) logic 1 = enable the cts interrupt. the 850 issues an interrupt when cts pin transitions from a logic 0 to a logic 1 as reported in msr register. the interrupt is cleared by reading the msr register. fifo control register (fcr) this register is used to enable the fifos, clear the fifos, set the transmit/receive fifo trigger levels, and select the dma mode. the dma, and fifo modes are defined as follows: dma mode mode 0 set and enable the interrupt for each single transmit or receive operation, and is similar to the st16c450 mode. transmit ready (-txrdy) will go to a logic 0 when ever an empty transmit space is available in the transmit holding register (thr). receive ready (-rxrdy) will go to a logic 0 whenever the receive holding register (rhr) is loaded with a character. mode 1 set and enable the interrupt in a block mode operation. the transmit interrupt is set when the transmit fifo is below the programmed trigger level. - txrdy remains a logic 0 as long as one empty fifo location is available. the receive interrupt is set when the receive fifo fills to the programmed trigger level. however the fifo continues to fill regardless of the programmed level until the fifo is full. -rxrdy remains a logic 0 as long as the fifo fill level is above the programmed trigger level. fcr bit-0: logic 0 = disable the transmit and receive fifo. (normal default condition) logic 1 = enable the transmit and receive fifo. this bit must be a 1 when other fcr bits are written to or they will not be programmed. fcr bit-1: logic 0 = no fifo receive reset. (normal default condition) logic 1 = clears the fifo counter and resets the pointers logic (the receive shift register is not cleared or altered). this bit will return to a logic 0 after clearing the fifo.
xr16c850 28 rev. 1.20 fcr bit-2: logic 0 = no fifo transmit reset. (normal default condition) logic 1 = clears the fifo counter and resets the pointers logic (the transmit shift register is not cleared or altered). this bit will return to a logic 0 after clearing the fifo. fcr bit-3: logic 0 = set dma mode 0. (normal default condition) logic 1 = set dma mode 1. transmit operation in mode 0: when the 850 is in the st16c450 mode (fifos dis- abled, fcr bit-0 = logic 0) or in the fifo mode (fifos enabled, fcr bit-0 = logic 1, fcr bit-3 = logic 0) and when there are no characters in the transmit fifo or transmit holding register, the -txrdy pin will be a logic 0. once active the -txrdy pin will go to a logic 1 after the first character is loaded into the transmit holding register. receive operation in mode 0: when the 850 is in mode 0 (fcr bit-0 = logic 0) or in the fifo mode (fcr bit-0 = logic 1, fcr bit-3 = logic 0) and there is at least one character in the receive fifo, the -rxrdy pin will be a logic 0. once active the - rxrdy pin will go to a logic 1 when there are no more characters in the receiver. transmit operation in mode 1: when the 850 is in fifo mode ( fcr bit-0 = logic 1, fcr bit-3 = logic 1 ), the -txrdy pin will be a logic 1 when the transmit fifo is completely full. it will be a logic 0 if one or more fifo locations are empty. receive operation in mode 1: when the 850 is in fifo mode (fcr bit-0 = logic 1, fcr bit-3 = logic 1) and the trigger level has been reached, or a receive time out has occurred, the -rxrdy pin will go to a logic 0. once activated, it will go to a logic 1 after there are no more characters in the fifo. fcr bit 4-5: (logic 0 or cleared is the default condition, tx trigger level = none) the xr16c850 provides 4 user selectable trigger levels, the fctr bits 4-5 selects one of the following tables. these bits are used to set the trigger level for the transmit fifo interrupt. the xr16c850 will issue a transmit empty interrupt when the number of characters in fifo drops below the selected trigger level. trigger table-a (transmit) default setting after reset, st16c550 mode bit-5 bit-4 fifo trigger level x x none trigger table-b (transmit) bit-5 bit-4 fifo trigger level 00 16 01 8 10 24 11 30 trigger table-c (transmit) bit-5 bit-4 fifo trigger level 00 8 01 16 10 32 11 56 trigger table-d (transmit) bit-5 bit-4 fifo trigger level x x user programmable trigger levels fcr bit 6-7: (logic 0 or cleared is the default condition, rx trigger level =8) these bits are used to set the trigger level for the receiver fifo interrupt. the interrupt will trigger again when rx data is unloaded below the threshold and incoming data fills it back up to the trigger level. the fctr bits 4-5 selects one of the following tables.
xr16c850 29 rev. 1.20 interrupt status register is read, the interrupt status is cleared. however it should be noted that only the current pending interrupt is cleared by the read. a lower level interrupt may be seen after re-reading the interrupt status bits. the interrupt source table 6 (below) shows the data values (bit 0-5) for the six prioritized interrupt levels and the interrupt sources associated with each of these interrupt levels. trigger table-a (receive) default setting after reset, st16c550 mode bit-7 bit-6 fifo trigger level 00 1 01 4 10 8 11 14 trigger table-b (receive) bit-7 bit-6 fifo trigger level 00 8 01 16 10 24 11 28 trigger table-c (receive) bit-7 bit-6 fifo trigger level 00 8 01 16 10 56 11 60 trigger table-d (receive) bit-7 bit-6 fifo trigger level x x user programmable trigger levels interrupt status register (isr) the 850 provides six levels of prioritized interrupts to minimize external software interaction. the interrupt status register (isr) provides the user with six interrupt status bits. performing a read cycle on the isr will provide the user with the highest pending interrupt level to be serviced. no other interrupts are acknowledged until the pending interrupt is serviced. whenever the
xr16c850 30 rev. 1.20 table 6, interrupt source table priority [ isr bits ] level b it-5 bit-4 bit-3 bit-2 bit-1 bit-0 source of the interrupt 1 0 0 0 1 1 0 lsr (receiver line status register) 2 0 0 0 1 0 0 rxrdy (received data ready) 2 0 0 1 1 0 0 rxrdy (receive data time out) 3 0 0 0 0 1 0 txrdy ( transmitter holding register empty) 4 0 0 0 0 0 0 msr (modem status register) 5 0 1 0 0 0 0 rxrdy (received xoff signal)/ special character 6 1 0 0 0 0 0 cts, rts change of state isr bit-0: logic 0 = an interrupt is pending and the isr contents may be used as a pointer to the appropriate interrupt service routine. logic 1 = no interrupt pending. (normal default condi- tion) isr bit 1-3: (logic 0 or cleared is the default condition) these bits indicate the source for a pending interrupt at interrupt priority levels 1, 2, and 3 (see interrupt source table). isr bit 4-5: (logic 0 or cleared is the default condition) these bits are enabled when efr bit-4 is set to a logic 1. isr bit-4 indicates that matching xoff character(s) have been detected. isr bit-5 indicates that cts, rts have been generated. note that once set to a logic 1, the isr bit-4 will stay a logic 1 until xon character(s) are received. isr bit 6-7: (logic 0 or cleared is the default condition) these bits are set to a logic 0 when the fifo is not being used. they are set to a logic 1 when the fifos are enabled line control register (lcr) the line control register is used to specify the asyn- chronous data communication format. the word length, the number of stop bits, and the parity are selected by writing the appropriate bits in this register. this register also has a secondary function to select 2 other register sets. the first is by setting bit-7 = 1 to select the baud rate divisor (dll and dlm) registers, and the second set of registers is selected when a bf hex is written to lcr to select the enhanced register set. lcr bit 0-1: (logic 0 or cleared is the default condition) these two bits specify the word length to be transmitted or received. the upper unused bit(s) in the received data byte is set to zero. bit-1 bit-0 word length 00 5 01 6 10 7 11 8 lcr bit-2: (logic 0 or cleared is the default condition) the length of stop bit is specified by this bit in conjunc- tion with the programmed word length. bit-2 word length stop bit length (bit time(s)) 0 5,6,7,8 1 1 5 1-1/2 1 6,7,8 2
xr16c850 31 rev. 1.20 lcr bit-3: parity or no parity can be selected via this bit. logic 0 = no parity (normal default condition) logic 1 = a parity bit is generated during the transmis- sion, the receiver checks and reports parity error in the lsr register. the parity is not presented in the received data byte. lcr bit-4: if the parity bit is enabled with lcr bit-3 set to a logic 1, lcr bit-4 selects the even or odd parity format. logic 0 = odd parity is generated by forcing an odd number of logic 1s in the transmitted data. the receiver must be programmed to check the same format. (nor- mal default condition) logic 1 = even parity is generated by forcing an even number of logic 1s in the transmitted data. the receiver must be programmed to check the same format. lcr bit-5: if the parity bit is enabled, lcr bit-5 selects the forced parity format. lcr bit-5 = logic 0, parity is not forced (normal default condition) lcr bit-5 = logic 1 and lcr bit-4 = logic 0, parity bit is forced to a logical 1 for the transmit and receive data. lcr bit-5 = logic 1 and lcr bit-4 = logic 1, parity bit is forced to a logical 0 for the transmit and receive data. lcr lcr lcr parity selection bit-3 bit-4 bit-5 0 x x no parity 1 0 0 odd parity 1 1 0 even parity 1 0 1 force parity 1 1 1 1 forced parity 0 lcr bit-6: when enabled the break control bit causes a break condition to be transmitted (the tx output is forced to a logic 0 state). this condition exists until disabled by setting lcr bit-6 to a logic 0. logic 0 = no tx break condition. (normal default condition) logic 1 = forces the transmitter output (tx) to a logic 0 for alerting the remote receiver to a line break condi- tion. lcr bit-7: the internal baud rate counter latch and enhance feature mode enable. logic 0 = divisor latch disabled. (normal default condi- tion) logic 1 = select baud rate divisors (dll and dlm) and enhanced feature register set enabled modem control register (mcr) this register controls the interface with the modem or a peripheral device. mcr bit-0: logic 0 = force -dtr output to a logic 1. (normal default condition) logic 1 = force -dtr output to a logic 0. mcr bit-1: logic 0 = force -rts output to a logic 1. (normal default condition) logic 1 = force -rts output to a logic 0. automatic rts may be used for hardware flow control by enabling efr bit-6 (see efr bit-6). mcr bit-2: logic 0 = set -op1 output to a logic 1. (normal default condition) logic 1 = set -op1 output to a logic 0. mcr bit-3: logic 0 = set -op2 output to a logic 1 (std mode). forces irqx outputs to three state mode during the pc mode. (normal default condition) logic 1 = set -op2 output to a logic 0 (std mode). forces the irqx outputs to the active mode during the pc mode. mcr bit-4: logic 0 = disable loop-back mode. (normal default condition) logic 1 = enable local loop-back mode (diagnostics). mcr bit-5: logic 0 = disable xon any function (for 16c550 compat- ibility). (normal default condition) logic 1 = enable xon any function. in this mode any rx character received will enable xon.
xr16c850 32 rev. 1.20 mcr bit-6: logic 0 = enable modem receive and transmit input/ output interface. (normal default condition) logic 1 = enable infrared irda receive and transmit inputs/outputs. while in this mode, the tx/rx output/ inputs are routed to the infrared encoder/decoder. the data input and output levels will conform to the irda infrared interface requirement. as such, while in this mode the infrared tx output will be a logic 0 during idle data conditions. care must be taken into consideration in the design not to over heat the ir led during powerup initialization state while tx output is still at logic 1. procedure to enable the ir encoder and decoder functions during initialization routine. write lcr with bf hex ; access to efr shadow register set efr bit-4 to logic 1 ; enable enhanced function bits write lcr with op. values ; set operating parameters set mcr bit-6 to logic 1 ; enable ir mode, tx pin goes logic 0 mcr bit-7: this bit overrides the clksel pin selection. logic 0 = divide by one. the input clock (crystal or external) is divided by sixteen and then presented to the programmable baud rate generator (bgr) without further modification, i.e., divide by one. (normal, default condition) logic 1 = divide by four. the divide by one clock described in mcr bit-7 equals a logic 0, is further divided by four (also see programmable baud rate generator section). line status register (lsr) this register provides the status of data transfers between the 850 and the cpu. lsr bit-0: logic 0 = no data in receive holding register or fifo. (normal default condition) logic 1 = data has been received and is saved in the receive holding register or fifo. lsr bit-1: logic 0 = no overrun error. (normal default condition) logic 1 = overrun error. a data overrun error occurred in the receive shift register. this happens when additional data arrives while the fifo is full. in this case the previous data in the shift register is overwritten. note that under this condition the data byte in the receive shift register is not transfer into the fifo, therefore the data in the fifo is not corrupted by the error. lsr bit-2: logic 0 = no parity error (normal default condition) logic 1 = parity error. the receive character does not have correct parity information and is suspect. in the fifo mode, this error is associated with the character at the top of the fifo. lsr bit-3: logic 0 = no framing error (normal default condition). logic 1 = framing error. the receive character did not have a valid stop bit(s). in the fifo mode this error is associated with the character at the top of the fifo. lsr bit-4: logic 0 = no break condition (normal default condition) logic 1 = the receiver received a break signal (rx was a logic 0 for one character frame time). in the fifo mode, only one break character is loaded into the fifo. lsr bit-5: this bit is the transmit holding register empty indica- tor. this bit indicates that the uart is ready to accept a new character for transmission. in addition, this bit causes the uart to issue an interrupt to cpu when the thr interrupt enable is set. the thr bit is set to a logic 1 when a character is transferred from the transmit holding register into the transmitter shift register. the bit is reset to logic 0 concurrently with the loading of the transmitter holding register by the cpu. in the fifo mode this bit is set when the transmit fifo is empty; it is cleared when at least 1 byte is written to the transmit fifo. lsr bit-6: this bit is the transmit empty indicator. this bit is set to a logic 1 whenever the transmit holding register and the transmit shift register are both empty. it is reset to logic 0 whenever either the thr or tsr contains a data character. in the fifo mode this bit is set to one whenever the transmit fifo and transmit shift register are both empty. lsr bit-7: logic 0 = no error (normal default condition)
xr16c850 33 rev. 1.20 logic 1 = at least one parity error, framing error or break indication is in the current fifo data. this bit is cleared when lsr register is read. modem status register (msr) this register provides the current state of the control interface signals from the modem, or other peripheral device that the 850 is connected to. four bits of this register are used to indicate the changed information. these bits are set to a logic 1 whenever a control input from the modem changes state. these bits are set to a logic 0 whenever the cpu reads this register. msr bit-0: logic 0 = no -cts change (normal default condition) logic 1 = the -cts input to the 850 has changed state since the last time it was read. a modem status interrupt will be generated. msr bit-1: logic 0 = no -dsr change (normal default condition) logic 1 = the -dsr input to the 850 has changed state since the last time it was read. a modem status interrupt will be generated. msr bit-2: logic 0 = no -ri change (normal default condition) logic 1 = the -ri input to the 850 has changed from a logic 0 to a logic 1. a modem status interrupt will be generated. msr bit-3: logic 0 = no -cd change (normal default condition) logic 1 = indicates that the -cd input to the 850 has changed state since the last time it was read. a modem status interrupt will be generated. msr bit-4: -cts functions as hardware flow control signal input if it is enabled via efr bit-7. the transmit holding register flow control is enabled/disabled by msr bit-4. flow control (when enabled) allows the starting and stopping the transmissions based on the external modem -cts signal. a logic 1 at the -cts pin will stop 850 transmis- sions as soon as current character has finished trans- mission. normally msr bit-4 bit is the compliment of the -cts input. however in the loop-back mode, this bit is equivalent to the rts bit in the mcr register. msr bit-5: dsr (active high, logical 1). normally this bit is the compliment of the -dsr input. in the loop-back mode, this bit is equivalent to the dtr bit in the mcr register. msr bit-6: ri (active high, logical 1). normally this bit is the compliment of the -ri input. in the loop-back mode this bit is equivalent to the op1 bit in the mcr register. msr bit-7: cd (active high, logical 1). normally this bit is the compliment of the -cd input. in the loop-back mode this bit is equivalent to the op2 bit in the mcr register. scratchpad register (spr) the xr16c850 provides a temporary data register to store 8 bits of user information. enhanced feature register (efr) enhanced features are enabled or disabled using this register. bits-0 through 4 provide single or dual character soft- ware flow control selection. when the xon1 and xon2 and/or xoff1 and xoff2 modes are selected (see table 7), the double 8-bit words are concatenated into two se- quential characters. efr bit 0-3: (logic 0 or cleared is the default condition) combinations of software flow control can be selected by programming these bits.
xr16c850 34 rev. 1.20 efr bit-4: enhanced function control bit. the content of the ier bits 4-7, isr bits 4-5, fcr bits 4-5, and mcr bits 5-7 are enabled when this bit is set to logic 1. after modifying these bits efr bit-4 can be set to a logic 0 to latch the new values. this feature prevents existing software from altering or overwriting the 850 enhanced functions. logic 0 = disable/latch enhanced features. ier bits 4- 7, isr bits 4-5, fcr bits 4-5, and mcr bits 5-7 are saved to retain the user settings, then ier bits 4-7, isr bits 4- 5, fcr bits 4-5, and mcr bits 5-7 are initialized to the default values shown in the internal register table. after a reset, the ier bits 4-7, isr bits 4-5, fcr bits 4-5, and mcr bits 5-7 are set to a logic 0 to be compatible with st16c550 mode. (normal default condition). logic 1 = enables the enhanced functions. when this bit is set to a logic 1 all enhanced features of the 850 are enabled and user settings stored during a reset will be restored. efr bit-5: logic 0 = special character detect disabled (normal default condition) logic 1 = special character detect enabled. the 850 compares each incoming receive character with xoff-2 data. if a match exists, the received data will be transferred to fifo and isr bit-4 will be set to indicate detection of special character. bit-0 in the x-registers corresponds with the lsb bit for the receive character. when this feature is enabled, the normal software flow control must be disabled (efr bits 0-3 must be set to a logic 0). efr bit-6: automatic rts is used for hardware flow control by enabling efr bit-6. the user must assert Crts to initiate this function. when auto rts is selected, an interrupt will be generated when the receive fifo is filled to the programmed rx trigger level and -rts will go to a logic 1 when it reaches the upper limit of the hysterisis level. -rts will return to a logic 0 when data is unloaded to the lower limit of the hysterisis. the state of this register bit changes with the status of the hardware flow control. -rts functions normally when hardware flow control is disabled. 0 = automatic rts flow control is disabled. (normal default condition) 1 = enable automatic rts flow control. cont-3 cont-2 cont-1 cont-0 tx, rx software flow controls 0 0 x x no transmit flow control 1 0 x x transmit xon1/xoff1 0 1 x x transmit xon2/xoff2 1 1 x x transmit xon1 and xon2/xoff1 and xoff2 x x 0 0 no receive flow control x x 1 0 receiver compares xon1/xoff1 x x 0 1 receiver compares xon2/xoff2 1011 transmit xon1/ xoff1. receiver compares xon1 and xon2, xoff1 and xoff2 0111 transmit xon2/xoff2 receiver compares xon1 and xon2/xoff1 and xoff2 1111 transmit xon1 and xon2/xoff1 and xoff2 receiver compares xon1 and xon2/xoff1 and xoff2 0011no transmit flow control receiver compares xon1 and xon2/xoff1 and xoff2 table 7. software flow control functions
xr16c850 35 rev. 1.20 efr bit-7: automatic cts flow control. logic 0 = automatic cts flow control is disabled. (normal default condition) logic 1 = enable automatic cts flow control. transmis- sion will stop when -cts goes to a logical 1. transmis- sion will resume when the -cts pin returns to a logical 0. feature control register (fctr) this register controls the xr16c850 new functions that are not available on st16c550 or st16c650a. fctr bit 0-1: user selectable -rts delay timer for hardware flow control application. after reset, these bits are set to 0 to select the next trigger level for hardware flow control. fctr fctr trigger bit-1 bit-0 level 0 0 next trigger level 0 1 4 char+trigger level 1 0 6 char+trigger level 1 1 8 char+trigger level fctr bit-2: 0 = select rx input as encoded irda data. 1 = select rx input as active high encoded irda data. fctr bit-3: auto rs-485 direction control. 0 = standard st16c550 mode. transmitter generates an interrupt when transmit holding register becomes empty and transmit shift register is shifting data out. 1 = enable auto rs485 direction control function. the direction control signal, -op1 pin, changes its output logic state from low to high one bit time after the last stop bit of the last character is shifted out. also, the transmit interrupt generation is delayed until the transmitter shift register becomes empty. the -op1 output pin will automatically return to logic high state when a data byte is loaded into the tx fifo. fctr bit 4-5: transmit / receive trigger table select. fctr fctr table bit-5 bit-4 0 0 table-a (tx/rx) 0 1 table-b (tx/rx) 1 0 table-c (tx/rx) 1 1 table-d (tx/rx) fctr bit-6: register mode select. 0 = scratch pad register is selected as general read and write register. st16c550 compatible mode. 1 = fifo count register, enhanced mode select reg- ister. number of characters in transmit or receive holding register can be read via scratch pad register when this bit is set. enhanced mode is selected when it is written into it. fctr bit-7: programmable trigger register select. 0 = receiver programmable trigger level register is selected. 1 = transmitter programmable trigger level register is selected. trigger level / fifo data count register (trg) user programmable transmit / receive trigger level register. trg bit 0-7: write only. these bits are used to program desired trigger levels that are not available in standard tables. trg bit 0-7: read only. transmit / receive fifo count. number of characters in transmit or receive fifo can be read via this register.
xr16c850 36 rev. 1.20 enhanced mode select register (emsr) this register is accessible only when fctr bit-6 is set to 1. emsr bit-0: write only 0 = receive fifo count register. the scratch pad register is used to provide the receive fifo count when it is read. 1 = transmit fifo count register. the scratch pad register is used to provide the transmit fifo count when it is read. emsr bit-1: write only 0 = normal. 1 = alternate receive - transmit fifo count. when emsr bit-0=1 and emsr bit-1=1, scratch pad register is used to provide the receive - transmit fifo count when it is read every alternate read cycle. the trg bit- 7 will provide fifo count mode information, trg bit- 7=0 receive mode, trg bit-7=1 transmit mode. emsr bit-2: write only this bit selects and enables the dma interface function on the 52-pin device, Cdack, -drq and tc become active. only tx or rx dma can be enabled at one time. 0 = enable rx dma 1 = enable tx dma emsr bit 3-7: reserved for future use. xr16c850 external reset conditions registers reset state ier ier bits 0-7 = logic 0 isr isr bit-0=1, isr bits 1-7 = logic 0 lcr, mcr bits 0-7 = logic 0 lsr lsr bits 0-4 = logic 0, lsr bits 5-6 = logic 1 lsr, bit 7 = logic 0 msr msr bits 0-3 = logic 0, msr bits 4-7 = logic levels of the input signals fcr, efr bits 0-7 = logic 0 fctr bits 0-7 = logic 0 emsr bits 0-7 = logic 0 scpad bits 0-7 = logic 1 signals reset state tx logic 1 -op1 logic 1 -op2 logic 1 -rts logic 1 -dtr logic 1 -rxrdy logic 1 (std mode),/ three state (pc mode) -txrdy logic 0 (std mode) / three state (pc mode) irqn/int logic 0 (std mode) / three state (pc mode)
xr16c850 37 rev. 1.20 t 1w ,t 2w clock pulse duration 20 20 ns t 3w oscillator/clock frequency 8 24 mhz t 4w address strobe width 50 25 ns t 5s address setup time 15 10 ns t 5h address hold time 10 5 ns t 6s address setup time 10 5 ns t 6h chip select hold time 0 0 ns t 7d -ior delay from chip select 10 10 ns note 1: t 7w -ior strobe width 50 25 ns t 7h chip select hold time from -ior 5 5 ns note 1: t 8d ior delay from chip select 8 8 ns t 9d read cycle delay 50 50 ns t 10d csout delay from chip select 15 10 ns 100 pf load t 11d -ior to -ddis delay 25 20 ns 100 pf load t 12d delay from -ior to data 35 25 ns t 12h data disable time 25 15 ns t 13d -iow delay from chip select 10 10 ns note 1: t 13w -iow strobe width 40 40 ns t 13h chip select hold time from -iow 0 0 ns t 14d -iow delay from address 10 10 ns note 1: t 15d write cycle delay 50 50 ns t 16s data setup time 20 15 ns t 16h data hold time 50 35 ns t 17d delay from -iow to output 50 50 ns 100 pf load t 18d delay to set interrupt from modem 50 35 ns 100 pf load input t 19d delay to reset interrupt from -ior 50 35 ns 100 pf load t 20d delay from stop to set interrupt 1 1 rclk t 21d delay from -ior to reset interrupt 200 200 ns 100 pf load t 22d delay from stop to interrupt 100 100 ns t 23d delay from initial int reset to transmit 8 24 8 24 rclk start t 24d delay from -iow to reset interrupt 175 175 ns t 25d delay from stop to set -rxrdy 1 1 rclk t 26d delay from -ior to reset -rxrdy 175 175 ns t 27d delay from -iow to set -txrdy 175 175 ns t 28d delay from start to reset -txrdy 8 8 rclk t r reset pulse width 40 40 ns n baud rate devisor 1 2 16 -1 1 2 16 -1 rclk note 1: applicable only when -as is tied low. ac electrical characteristics t a =0 - 70 c ( -40 - +85 c for ip, ij, iq packages), vcc=3.3 - 5.0 v 10% unless otherwise specified. symbol parameter limits limits units conditions 3.3 5.0 min max min max
xr16c850 38 rev. 1.20 absolute maximum ratings supply range 7 volts voltage at any pin gnd-0.3 v to vcc+0.3 v operating temperature -40 c to +85 c storage temperature -65 c to +150 c package dissipation 500 mw dc electrical characteristics t a =0 - 70 c ( -40 - +85 c for ip, ij, iq packages), vcc=3.3 - 5.0 v 10% unless otherwise specified. symbol parameter limits limits units conditions 3.3 5.0 min max min max v ilck clock input low level -0.3 0.6 -0.5 0.6 v v ihck clock input high level 2.4 vcc 3.0 vcc v v il input low level -0.3 0.8 -0.5 0.8 v v ih input high level 2.0 2.2 vcc v v ol output low level on all outputs 0.4 v i ol = 5 ma v ol output low level on all outputs 0.4 v i ol = 4 ma v oh output high level 2.4 v i oh = -5 ma v oh output high level 2.0 v i oh = -1 ma i il input leakage 10 10 m a i cl clock leakage 10 10 m a i cc avg power supply current 2.7 4 ma i sb avg stand by current 30 50 m a see test 1: c p input capacitance 5 5 pf test 1: for low power operation these pins should be left at logic 1 state: s1, s2, a4, a9, bus8/16, clk8/16, clksel, -dma, -dack, sel, tc and rx.
xr16c850 39 rev. 1.20 t3w -baudout 1/2 -baudout 1/3 -baudout 1/3> -baudout t1w t2w external clock x450-ck-1 clock timing
xr16c850 40 rev. 1.20 -ddis d0-d7 t12d t12h x550-rd-1 -as a0-a2 -cs2 cs1-cs0 -ior ior t4w t5s t5h t6s t6h t7w t7d t7h t9d t11d t11d t8d valid address valid active data active general read timing in "std mode"
xr16c850 41 rev. 1.20 -as a0-a2 -cs2 cs1-cs0 -iow iow d0-d7 t4w t5s t5h t6s t6h t13w t13d t13h t15d t16s x550-wd-1 t14d t16h valid address valid active data general write timing in "std mode"
xr16c850 42 rev. 1.20 a0-a9 -aen -ior d0-d7 t6s t7w t7d t7d t9d t12s t12h x650-rd-2 active data valid address active a0-a9 -aen -iow d0-d7 t6s t13w t13d t13h t15d t16s t16h x650-wd-2 valid address active active data general read timing in "pc mode" general write timing in "pc mode"
xr16c850 43 rev. 1.20 -iow iow -rts -dtr -cd -cts -dsr int -ior ior -ri t17d t18d t18d t19d t18d x450-md-1 active active change of state change of state active active active change of state change of state change of state active active modem input/output timing
xr16c850 44 rev. 1.20 stop bit parity bit data bits (5-8) d0 d1 d2 d3 d4 d5 d6 d7 5 data bits 6 data bits 7 data bits start bit rx next data start bit int -ior ior t20d t21d 16 baud rate clock x450-rx-1 active receive timing
xr16c850 45 rev. 1.20 stop bit parity bit data bits (5-8) d0 d1 d2 d3 d4 d5 d6 d7 start bit rx next data start bit -rxrdy -ior ior t25d t26d x550-rx-2 active data ready active receive ready timing in non fifo mode
xr16c850 46 rev. 1.20 stop bit parity bit data bits (5-8) d0 d1 d2 d3 d4 d5 d6 d7 start bit rx first byte that reaches the trigger level -rxrdy -ior ior t25d t26d x550-rx-3 active data ready active receive ready timing in fifo mode
xr16c850 47 rev. 1.20 stop bit parity bit data bits (5-8) d0 d1 d2 d3 d4 d5 d6 d7 5 data bits 6 data bits 7 data bits start bit tx next data start bit int t22d t24d 16 baud rate clock x450-tx-1 -iow iow t23d active active tx ready active transmit timing
xr16c850 48 rev. 1.20 stop bit parity bit data bits (5-8) d0 d1 d2 d3 d4 d5 d6 d7 start bit tx next data start bit -txrdy t28d x850-tx-2 -iow iow t27d byte #128 fifo full transmit ready timing in non fifo mode
xr16c850 49 rev. 1.20 stop bit parity bit data bits (5-8) d0 d1 d2 d3 d4 d5 d6 d7 5 data bits 6 data bits 7 data bits s tart bit tx -iow iow d0-d7 -txrdy byte #128 t28d t27d x850-tx-3 fifo full active transmit ready timing in fifo mode
xr16c850 50 rev. 1.20 uart frame data bits start stop 0000 0 11 111 tx irtx bit time 1/2 bit time 3/16 bit time uart frame data bits start stop 0000 0 11 111 rx irrx bit time 0-1 16x clock delay x650-ir-1 infrared transmit timing infrared receive timing
xr16c850 51 rev. 1.20
xr16c850 52 rev. 1.20
xr16c850 53 rev. 1.20
xr16c850 54 rev. 1.20
xr16c850 55 rev. 1.20 notice exar corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. exar corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. charts and schedules contained here in are only for illustration purposes and may vary depending upon a users specific application. while the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. exar corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. products are not authorized for use in such applications unless exar corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of exar corporation is adequately protected under the circumstances. copyright 1999 exar corporation datasheet june 1999 reproduction, in part or whole, without the prior written consent of exar corporation is prohibited.

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