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| motorola reserves the right to make changes without further notice to any products herein. motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. "typical" parameters can and do vary in different applications. all operating parameters, including "typicals" must be validated for each customer application by customer's technical experts. motorola does not convey any license under its patent rights nor the rights of others. motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the motorola product could create a situation where personal injury or death may occur. should buyer purchase or use motorola products for any such unintended or unauthorized application, buyer shall indemnify and hold motorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that motorola was negligent regarding the design or manufacture of the part. motorola and ! are registered trademarks of motorola, inc. motorola, inc. is an equal opportunity/affirmative action employer. ?motorola, inc. 1996 modular microcontroller family adc analog-to-digital converter reference manual f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc motorola reference manual iii paragraph title page section 1functional overview 1.1 analog subsystem .................................................................................... 1-1 1.2 digital control subsystem ......................................................................... 1-1 1.3 general-purpose i/o ................................................................................. 1-2 1.4 module configuration ................................................................................ 1-2 1.5 bus organization ....................................................................................... 1-3 1.6 memory map ............................................................................................. 1-3 section 2 signal descriptions 2.1 analog/digital input pins (an[7:0]/pada[7:0]) .......................................... 2-1 2.2 digital output pins (padb[7:0]) ................................................................ 2-1 2.3 analog reference pins .............................................................................. 2-1 2.4 analog supply pins ................................................................................... 2-2 section 3configuration and control 3.1 adc bus interface unit ............................................................................. 3-1 3.2 module configuration ................................................................................ 3-1 3.2.1 low-power stop operation ............................................................... 3-1 3.2.2 freeze mode operation .................................................................... 3-2 3.2.3 privilege levels ................................................................................. 3-2 3.2.4 adc module configuration register (adcmcr) .............................. 3-3 3.3 general-purpose i/o ................................................................................. 3-3 3.4 adc test register (adctest) ................................................................ 3-4 3.5 initialization checklist ................................................................................ 3-4 section 4 analog subsystem 4.1 multiplexer ................................................................................................. 4-1 4.2 sample buffer amplifier ............................................................................. 4-1 4.3 rc dac array ........................................................................................... 4-2 4.4 comparator ............................................................................................... 4-2 4.5 successive approximation register (sar) ............................................... 4-2 section 5 digital control subsystem 5.1 conversion timing .................................................................................... 5-1 5.2 clock and prescaler control ...................................................................... 5-3 5.3 final sample time .................................................................................... 5-3 5.4 resolution ................................................................................................. 5-4 5.5 conversion mode ...................................................................................... 5-4 table of contents f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola adc iv reference manual (continued) paragraph title page table of contents 5.6 channel selection ..................................................................................... 5-6 5.7 control and status registers .................................................................... 5-7 5.7.1 adc control register 0 (adctl0) .................................................... 5-7 5.7.2 adc control register 1 (adctl1) .................................................... 5-8 5.7.3 adc status register (adstat) ........................................................ 5-9 5.8 result registers (rslt0?slt7) ............................................................ 5-9 section 6 pin connection considerations 6.1 analog reference pins .............................................................................. 6-1 6.2 analog power pins .................................................................................... 6-1 6.3 analog input pins ...................................................................................... 6-2 6.3.1 settling time for the external circuit ................................................. 6-4 6.3.2 error resulting from leakage ........................................................... 6-4 appendix a electrical characteristics appendix b memory map and registers b.1 memory map ............................................................................................ b-1 b.2 registers .................................................................................................. b-2 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc motorola reference manual v figure title page 1-1 adc block diagram ....................................................................................... 1-2 5-1 8-bit conversion timing ................................................................................. 5-2 5-2 10-bit conversion timing ............................................................................... 5-2 5-3 adc clock and prescaler control .................................................................. 5-3 6-1 analog input circuitry ..................................................................................... 6-1 6-2 errors resulting from clipping ....................................................................... 6-2 6-3 electrical model of an a/d input pin ............................................................... 6-3 a-1 circuit and quantization error in 8-bit conversions ....................................... a-4 a-2 circuit and quantization error in 10-bit conversions ..................................... a-5 list of illustrations f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola adc vi reference manual (continued) figure title page list of illustrations f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc motorola reference manual vii table title page 1-1 adc module memory map .................................................................................... 1-4 3-1 frz field selection ............................................................................................... 3-2 5-1 prescaler output.................................................................................................... 5-3 5-2 sts field selection ............................................................................................... 5-4 5-3 conversion mode bits............................................................................................ 5-4 5-4 adc conversion modes ........................................................................................ 5-4 5-5 single-channel conversions ................................................................................. 5-6 5-6 multiple-channel conversions............................................................................... 5-7 6-1 external circuit settling time (10-bit conversions)............................................... 6-4 6-2 error resulting from input leakage (i off )............................................................. 6-5 a-1 maximum ratings.................................................................................................. a-1 a-2 adc dc electrical characteristics (operating) ..................................................... a-2 a-3 adc ac characteristics (operating)..................................................................... a-2 a-4 analog converter characteristics (operating) ...................................................... a-3 list of tables f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola adc viii reference manual (continued) table title page list of tables f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc functional overview motorola reference manual 1-1 section 1functional overview the analog-to-digital converter (adc), a module in motorola's family of modular micro- controllers, is a unipolar, successive-approximation converter with eight modes of op- eration and selectable 8- or 10-bit resolution. monotonicity is guaranteed for both 8- and 10-bit conversions. with a 16.78-mhz system clock, the adc can perform an 8- bit single conversion in 8 microseconds or a 10-bit single conversion in 9 microsec- onds. the adc contains an analog and a digital subsystem. figure 1-1 is a functional block diagram of the adc module. 1.1 analog subsystem the analog subsystem consists of a multiplexer, an input sample amplifier, a resistor- capacitor digital-to-analog converter (rc dac) array, and a high-gain comparator. the multiplexer selects one of eight internal or eight external signal sources for con- version. the sample amplifier buffers external high-impedance sources from the inter- nal circuitry. the rc dac array performs two functions: it acts as a sample-and-hold circuit, and it provides the digital-to-analog comparison output necessary for succes- sive approximation conversion. the comparator indicates whether each successive output of the rc dac array is higher or lower than the sampled input. section 4 an- alog subsystem describes this subsystem in greater detail. 1.2 digital control subsystem the digital control subsystem contains registers and logic to control the conversion process. control registers and associated logic select the conversion resolution (eight or ten bits), multiplexer input, conversion sequencing mode, sample time, and adc clock cycle. as each input is converted, the digital control subsystem stores the result, one bit at a time, in the successive approximation register (sar) and then transfers the result to one of eight result registers. each result is available in three formats (right- justified unsigned, left-justified signed, and left-justified unsigned), depending on the address from which it is read. section 5 digital control subsystem de- scribes the digital control functions in detail. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola functional overview adc 1-2 reference manual figure 1-1 adc block diagram 1.3 general-purpose i/o in addition to use as multiplexer inputs, the eight analog inputs can be used as a gen- eral-purpose digital input port (port ada), provided signals are within logic level spec- ification. port adb is a dedicated output port. a port data register (pdr) is used to access data from these ports. refer to section 2 signal descriptions and 3.3 general-purpose i/o for more information on ports ada and adb. 1.4 module configuration the adc module configuration register (adcmcr) controls the interaction between the adc and other modules. low-power stop mode and freeze mode are adc oper- ating modes associated with assertion of imb signals by other microcontroller modules sar rc dac array and comparator analog mux and sample buffer amp clk select/ prescale an6/pada6 an5/pada5 an4/pada4 an3/pada3 an2/pada2 an1/pada1 an0/pada0 v rh v rl reference v dda v ssa supply adc bus interface unit intermodule bus (imb) reserved reserved reserved reserved v rh v rl (v rh ? rl )/2 reserved mode and timing control internal connections port ada data register result 7 result 6 result 5 result 4 result 3 result 2 result 1 result 0 padb6 padb5 padb4 padb3 padb2 padb1 padb0 an7/pada7 padb7 port adb data register f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc functional overview motorola reference manual 1-3 or by external sources. the adcmcr also determines the privilege level at which most adc registers operate. refer to 3.2 module configuration for additional infor- mation. 1.5 bus organization the adc bus interface unit (abiu) serves as an interface between the adc and the intermodule bus (imb). the imb handles communication between the adc and other microcontroller modules and supplies timing signals to the adc. for additional infor- mation on the abiu, refer to 3.1 adc bus interface unit . 1.6 memory map the adc module is mapped into 32 words of address space (see table 1-1 ). five words are control and status registers, one word is digital port data, and 24 words pro- vide access to the results of a/d conversion (eight addresses for each type of convert- ed data). two words are reserved for expansion. the addresses provided in table 1- 1 and elsewhere in this manual are offsets from the adc base address. for the pre- cise locations of these registers, consult the user's manual for the specific microcon- troller unit (mcu). the column labeled ?ccess?in table 1-1 specifies which registers are supervisor only and which can be programmed to operate at either access level. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola functional overview adc 1-4 reference manual s = supervisor-accessible only s/u = supervisor- or user-accessible depending on state of the supv bit in the adcmcr table 1-1 adc module memory map address access control registers $xxxx00 s module configuration register (adcmcr) $xxxx02 s adc test register (adctest) $xxxx04 s (reserved) $xxxx06 s/u port data register (pdr) $xxxx08 s/u (reserved) $xxxx0a s/u adc control register 0 (adctl0) $xxxx0c s/u adc control register 1 (adctl1) $xxxx0e s/u adc status register (adstat) address access right-justified unsigned result registers $xxxx10 s/u adc result register 0 (rslt0) $xxxx12 s/u adc result register 1 (rslt1) $xxxx14 s/u adc result register 2 (rslt2) $xxxx16 s/u adc result register 3 (rslt3) $xxxx18 s/u adc result register 4 (rslt4) $xxxx1a s/u adc result register 5 (rslt5) $xxxx1c s/u adc result register 6 (rslt6) $xxxx1e s/u adc result register 7 (rslt7) address access left-justified signed result registers $xxxx20 s/u adc result register 0 (rslt0) $xxxx22 s/u adc result register 1 (rslt1) $xxxx24 s/u adc result register 2 (rslt2) $xxxx26 s/u adc result register 3 (rslt3) $xxxx28 s/u adc result register 4 (rslt4) $xxxx2a s/u adc result register 5 (rslt5) $xxxx2c s/u adc result register 6 (rslt6) $xxxx2e s/u adc result register 7 (rslt7) address access left-justified unsigned result registers $xxxx30 s/u adc result register 0 (rslt0) $xxxx32 s/u adc result register 1 (rslt1) $xxxx34 s/u adc result register 2 (rslt2) $xxxx36 s/u adc result register 3 (rslt3) $xxxx38 s/u adc result register 4 (rslt4) $xxxx3a s/u adc result register 5 (rslt5) $xxxx3c s/u adc result register 6 (rslt6) $xxxx3e s/u adc result register 7 (rslt7) f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc signal descriptions motorola reference manual 2-1 section 2 signal descriptions the adc uses up to 20 pins. up to eight pins are analog inputs (which can also be used as digital inputs), two pins are analog reference connections, and two pins are analog supply connections. in addition, eight pins serve as digital output pins in certain microcontroller systems. in systems not requiring these pins, they are not implement- ed, and the outputs from the module are not connected. refer to the appropriate mi- crocontroller user's manual for specific information. 2.1 analog/digital input pins (an[7:0]/pada[7:0]) each of the eight analog input pins (an[7:0]) is connected to a multiplexer in the adc. the multiplexer selects an analog input to convert to digital data. input voltages to the multiplexer must be between v rh and v rl . refer to section 6 pin connection considerations for recommendations on filtering the analog inputs. the analog input pins can also be read as digital inputs, provided the applied voltage is within the limits specified in appendix a electrical characteristics . when used as digital inputs, the pins are organized into an 8-bit port, port ada. data for port a is latched in the lower half of the 16-bit port data register (pdr). the digital inputs are then referred to as pada[7:0]. when used for digital input, each of these pins is conditioned by a synchronizer with an enable feature. the synchronizer is not enabled until the actual imb bus cycle addressing the pdr begins. this minimizes the high-current effect of mid-level signals on the inputs. this is particularly important when some of the inputs are being used as digital inputs and some as analog inputs. refer to 3.3 general-purpose i/o for more information on port ada. 2.2 digital output pins (padb[7:0]) the eight digital output pins (padb[7:0]) make up port adb, an output-only port. data for port adb is latched in the upper half of the pdr. on some mcus, these pins are left unconnected and port adb is not implemented. a read of the upper byte of the port data register returns the digital value in the output register of port adb. refer to 3.3 general-purpose i/o for more information on this output port. 2.3 analog reference pins separate high (v rh ) and low (v rl ) analog reference voltages are connected to the analog reference pins. because they are separated from the analog power supply pins (v dda and v ssa ), the reference pins can be connected to regulated and filtered sup- plies that allow the adc to achieve its highest degree of accuracy. refer to section 6 pin connection considerations for recommendations on filtering and con- ditioning the analog reference inputs. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola signal descriptions adc 2-2 reference manual the required reference voltage levels are provided in appendix a electrical characteristics . 2.4 analog supply pins pins v dda and v ssa supply power to the analog circuitry associated with the sample amplifier and rc dac array. other circuitry in the adc is powered from the digital power bus (pins v ddi and v ssi ). dedicated power for the rc dac array is necessary to isolate sensitive analog circuitry from noise on the digital power bus. refer to ap- pendix a electrical characteristics for precise electrical specifications. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc configuration and control motorola reference manual 3-1 section 3configuration and control other microcontroller modules communicate with the adc module via the intermodule bus (imb). the adc bus interface unit (abiu) coordinates imb activity with internal adc bus activity. the first part of this section explains the operation of the abiu. the second part of this section describes the adc module configuration register (adcm- cr), which contains bits used to configure the adc module. the final parts of this sec- tion discuss the general-purpose i/o functions of the adc module and provide a checklist for initializing the adc. 3.1 adc bus interface unit the abiu is designed to act as a slave device on the imb. the imb handles commu- nication between the adc and other microcontroller modules and supplies timing sig- nals to the adc. the abiu provides imb bus cycle termination and synchronizes internal adc signals with imb signals. the abiu also manages data bus routing to ac- commodate the three conversion data formats and controls the interface to the adc internal bus. adc registers are updated immediately when written to. however, if a conversion is in progress when a control bit is written, conversion halts and must be restarted before the new control parameter can take effect. communication between the imb and the adc is interleaved with internal adc com- munication. adc register accesses by the host system require bus cycles of three mcu clocks, so that each bus cycle contains six clock edges. internal i/o (sar to re- sult registers) and i/o from the imb occur during pre-assigned, non-conflicting times. this ensures that the adc can access the sar and result registers at all times. 3.2 module configuration the adcmcr contains bits that control the interaction of the adc module with other mcu modules. these bits place the adc in low-power or normal operation, determine the reaction of the adc module to assertion of the cpu freeze command, and de- termine the privilege level required to access most adc registers. 3.2.1 low-power stop operation when the stop bit in the adcmcr is set, the imb clock signal internal to the adc is disabled. this places the module in an idle state and minimizes power consumption. the bus interface unit does not shut down and adc registers are still accessible. any conversion in progress when stop is set is aborted. software can write to the adcmcr to set the stop bit. in addition, system reset (ei- ther internally or externally generated) sets this bit. following either of these condi- tions, the stop bit must be cleared before the adc can be used. because analog circuit bias currents are turned off when stop is set, the adc requires recovery time after the stop bit is cleared. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola configuration and control adc 3-2 reference manual execution of the cpu lpstop command can place the entire modular microcontrol- ler, including the adc, in low-power stop mode by turning off the system clock. this command does not set the stop bit in the adcmcr. before issuing the lpstop command, the user should assert the stop bit in the adcmcr so that the module stops in a known state. 3.2.2 freeze mode operation when the cpu enters background debugging mode, the freeze signal is asserted. the adc can respond to internal assertion of freeze in three ways: it can ignore freeze assertion, finish the current conversion and then freeze, or freeze immedi- ately. the type of response is determined by the value of the frz[1:0] field in the ad- cmcr (see table 3-1 ). when the adc freezes, the adc clock stops and all sequential activity ceases. con- tents of control and status registers remain valid while frozen. when the freeze sig- nal is negated, adc activity resumes. if the adc freezes during a conversion, activity resumes with the next step in the con- version sequence. however, capacitors in the analog conversion circuitry may dis- charge while the adc is frozen, and conversion results may be inaccurate. 3.2.3 privilege levels to protect system resources, the processor in certain mcus can operate at either of two privilege levels: user or supervisor. in systems that support privilege levels, ac- cesses of the adcmcr and adctest registers are permissible only when the cpu is operating at the supervisor privilege level. the remaining adc registers are pro- grammable to permit supervisor access only or to permit access when the cpu is op- erating at either privilege level. if the supv bit in the adcmcr is set, access to adc registers is permitted only when the cpu is operating at the supervisor level. if supv is clear, then both user and su- pervisor accesses of all registers other than the adcmcr and adctest register are permitted. the adc does not respond to a read or write of a supervisor-access register when the cpu is operating at the user privilege level. attempting such a read or write results in the bus access being transferred externally. refer to the sim or scim section of the appropriate mcu user's manual for details on external bus cycles to unimplemented locations. table 3-1 frz field selection frz response 00 ignore freeze 01 reserved 10 finish conversion, then freeze 11 freeze immediately f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc configuration and control motorola reference manual 3-3 mcus that do not support privilege levels always operate at the supervisor level, so that adc registers are always accessible. 3.2.4 adc module configuration register (adcmcr) the adcmcr contains fields and bits that control freeze and stop modes and deter- mine the privilege level required to access most adc registers. stop ?stop mode 0 = normal operation 1 = low-power operation frz[1:0] ?freeze the frz field determines adc response to assertion of the freeze signal by the cpu. 00 = ignore freeze 01 = reserved 10 = finish conversion, then freeze 11 = freeze immediately supv ?supervisor/user 0 = user access permitted to registers controlled by the supv bit 1 = supervisor access only permitted to adc registers 3.3 general-purpose i/o two digital ports are associated with the adc. these ports are accessed through the 16-bit port data register (pdr). port ada, an input-only port, uses the eight analog in- put pins. (certain mcus may provide fewer than eight analog input pins. refer to the appropriate mcu user's manual for details.) data for port ada is accessed in the lower half of the pdr. the digital level of an input port pin may be read at any time. a read of the pdr does not affect an a/d conversion in progress. use of any port a pin for digital input does not preclude the use of any other port a pin for analog input. if the signal on the input pin is not within v ih and v il specification (i.e., if the signal is in the dead band region), a read of the pdr returns an undetermined value. port adb, an output-only port, uses pins padb[7:0]. data for port adb is latched in the upper half of the pdr. on some mcus, port adb is not implemented. on these mcus, reads of the upper half of the pdr return whatever value was last written to the upper half of the register. adcmcr ?adc module configuration register $xxxx00 15 14 13 12 8 7 6 0 stop frz not used supv not used reset: 1 0 0 0 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola configuration and control adc 3-4 reference manual 3.4 adc test register (adctest) adctest ?adc test register $xxxx06 adctest is used only during factory testing of the mcu. 3.5 initialization checklist to initialize the adc submodule and begin a conversion sequence, follow these steps: 1. write to the adcmcr to ensure the stop and freeze bits are cleared and assign the desired value to the supv bit. 2. write to adctl0 to select the sample time, adc clock prescaler, and 8- or 10- bit resolution. 3. write to adctl1 to select the conversion mode (scan, mult, and s8cm bits) and conversion channel or channels (cd:ca) and to begin a conversion se- quence. once a conversion sequence has begun, the type of conversion mode selected deter- mines the programming sequence. refer to section 5 digital control sub- system for additional information on conversion modes and the adc control and status registers. pdr ?port data register $xxxx02 15 8 7 0 port adb output data port ada input data reset: 0 0 0 0 0 0 0 0 state of input pins f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc analog subsystem motorola reference manual 4-1 section 4 analog subsystem this section describes the operation of the analog subsystem. understanding this sub- system is helpful in designing adc applications and in using the digital control func- tions that regulate a/d conversion. refer to section 6 pin connection considerations for adc design considerations and section 5 digital con- trol subsystem for details concerning digital control functions. the analog subsystem consists of a multiplexer, sample capacitors, a buffer amplifier, an rc dac array, and a high-gain comparator. comparator output is used to se- quence the successive approximation register (sar). since the sar, like the rest of the analog subsystem, is not directly accessible to user software, its description is in- cluded in this section. 4.1 multiplexer the multiplexer selects one of eight external or eight internal sources for conversion. the eight internal sources include v rh , v rl, (v rh ?v rl ) / 2, and five reserved chan- nels. multiplexer operation is controlled by channel selection field [cd:ca] in adctl1. refer to 5.6 channel selection for details on selecting a conversion channel. the multiplexer contains positive clamping and negative stress protection circuitry. this circuitry prevents voltages (within certain limits) on other input channels from af- fecting the current conversion. 4.2 sample buffer amplifier each of the eight external input channels is associated with a sample capacitor and share a single sample buffer amplifier. after a conversion is initiated, the multiplexer output is connected to the sample capacitor at the input of the sample buffer amplifier for the first two adc clock cycles of the sampling period. the sample amplifier buffers the input channel from the relatively large capacitance of the rc dac array. the input channel sees only the small sample capacitors during this period. during the second two adc clock cycles of the sampling period, the sample capacitor is disconnected from the multiplexer, and the stored level in the sample capacitor is transferred to the rc dac array via the sample buffer amplifier. during the third part of the sampling period, the sample capacitor and amplifier are by- passed, and the multiplexer input charges the rc dac array directly. charging the rc dac array directly once the stored voltage level approaches the input voltage allows the adc to achieve a high degree of accuracy. moreover, since the voltage on the rc dac array is nearly equal to the external voltage by the start of this third period, this rc dac voltage presents very little loading to the external circuitry. this results in higher allowable input impedance and virtually no charge-sharing between channels. the length of this third period is determined by the value in the sts field of adctl0. refer to 5.1 conversion timing for additional information on adc conversion timing. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola analog subsystem adc 4-2 reference manual 4.3 rc dac array the rc dac array consists of binary-weighted capacitors and a resistor-divider chain. the array performs two functions: it acts as a sample-and-hold circuit during conver- sion and provides each successive digital-to-analog comparison voltage to the com- parator. conversion begins with msb comparison and ends with lsb comparison. array switching is controlled by the digital subsystem. 4.4 comparator the comparator indicates whether each approximation output from the rc dac array during resolution is higher or lower than the sampled input voltage. comparator output is fed to the digital control logic, which sets or clears each bit in the successive approx- imation register in sequence, msb first. 4.5 successive approximation register (sar) the sar accumulates the result of each conversion one bit at a time, starting with the most significant bit. at the start of the resolution period, the msb of the sar is set, and all less significant bits are cleared. depending on the result of the first comparison, the msb is either left set or cleared. each successive bit is set or left cleared in descend- ing order until all eight or ten bits have been resolved. when conversion is complete, the content of the sar is transferred to the appropriate result register, where it can be read by software. the sar itself is not accessible to user software. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc digital control subsystem motorola reference manual 5-1 section 5 digital control subsystem the digital control subsystem includes control and status registers, clock and prescal- er control logic, channel and reference select logic, conversion sequence control logic, and eight result registers. the successive approximation register, which holds each conversion result before it is transferred to the appropriate result register, is discussed in section 4 analog subsystem . adctl0 and adctl1 (adc control registers 0 and 1) and associated logic select the conversion resolution (8 or 10 bits), input channel, conversion mode, sample time, and adc clock cycle. adstat (the adc status register) contains flags indicating the com- pletion of a/d conversions. writing to adctl1 initiates a conversion. conversion results are stored, one bit at a time, in the sar. results are discrete val- ues between 0 and 255 (2 8 ?1) for 8-bit conversions and between 0 and 1023 (2 10 1) for 10-bit conversions. one binary unit = (v rh v rl ) / 2 n , where n = 8 or 10. each converted result is transferred from the sar to bits [7:0] (for 8-bit conversion) or [9:0] (for 10-bit conversion) of the appropriate result register. each result is available in three formats (right-justified unsigned, left-justified signed, and left-justified unsigned), depending on the address from which it is read. the following subsections discuss control functions involving the control and status registers. register diagrams are provided later in this section. (they are also provided in appendix b memory map and registers .) 5.1 conversion timing total conversion time is made up of initial sample time, transfer time, final sample time, and resolution time. initial sample time refers to the time during which the selected in- put channel is connected to the sample capacitor at the input of the sample buffer am- plifier. during the transfer period, the sample capacitor is disconnected from the multiplexer, and the stored voltage is buffered and transferred to the rc dac array. during the final sampling period, the sample capacitor and amplifier are bypassed, and the multiplexer input charges the rc dac array directly. during the resolution pe- riod, the voltage in the rc dac array is converted to a digital value and stored in the sar. initial sample time and transfer time are fixed at 2 adc clock cycles each. final sample time can be 2, 4, 8, or 16 adc clock cycles, depending on the value of the sts field in adctl0. (refer to 5.3 final sample time .) resolution time is 10 cycles for 8-bit conversion and 12 cycles for 10-bit conversion. transfer and resolution therefore require a minimum of 16 adc clocks (8 m s with a 2.1- mhz adc clock) for 8-bit resolution or 18 adc clocks (9 m s with a 2.1-mhz adc clock) for 10-bit resolution. if the user selects the maximum final sample time period of 16 adc clocks, the total conversion time is 15 m s for an 8-bit conversion or 16 m s for a 10-bit conversion (with a 2.1-mhz adc clock). f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola digital control subsystem adc 5-2 reference manual figure 5-1 and figure 5-2 illustrate the timing for 8- and 10-bit conversions, respec- tively. these diagrams assume a final sampling period of two adc clocks. figure 5-1 8-bit conversion timing figure 5-2 10-bit conversion timing ch 8 ch 7 ch 6 ch 5 ch 4 ch 3 ch 2 ch 1 scf flag set here and sequence ends if in the 4 channel mode scf flag set here and sequence ends if in the 8 channel mode end 6 cycles 16 1 transfer conversion to result register and set ccf resolution time final sample time initial sample time transfer time 1 cycle sar6 1 cycle sar5 1 cycle sar4 1 cycle sar3 1 cycle sar2 1 cycle sar1 1 cycle sar0 1 cycle eoc 2 cycles sar7 successive approximation sequence sample and transfer period ch 8 ch 7 ch 6 ch 5 ch 4 ch 3 ch 2 ch 1 scf flag set here and sequence ends if in the 4-channel mode scf flag set here and sequence ends if in the 8-channel mode 1 cycle end 6 cycles 16 1 transfer conversion to result register and set ccf resolution time sar8 final sample time initial sample time transfer time 1 cycle sar7 1 cycle sar6 1 cycle sar5 1 cycle sar4 1 cycle sar3 1 cycle sar2 1 cycle sar1 1 cycle sar0 1 cycle eoc 2 cycles sar9 successive approximation sequence sample and transfer period f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc digital control subsystem motorola reference manual 5-3 5.2 clock and prescaler control the adc clock is derived from the system clock by a programmable prescaler. the prescaler has two stages. the first stage is a 5-bit modulus counter contained in the prs field in adctl0. the system clock is divided by this value + 1 and then fed to the second stage, a divide-by-two circuit, to generate the adc clock. figure 5? illustrates the relationship of adc clock to system clock. figure 5-3 adc clock and prescaler control adc clock frequency must be between 0.5 and 2.1 mhz. the reset value of the prs field is %00011, which divides a nominal 16.78 mhz system clock by eight, yielding maximum adc clock frequency. the clock generation circuitry ensures that the adc clock can never be faster than one fourth the system clock speed. thus there are a minimum of four full imb clock cycles for each adc clock cycle. table 5-1 shows prescaler output values and associated minimum and maximum sys- tem clock speeds. 5.3 final sample time during the final sample period, the selected channel is connected directly to the rc dac array for the specified sample time. the value of the sts (sample time select) field in adctl0 determines final sample time in adc clock cycles. the sample period is thus determined by both the prs field (which controls the adc clock period) and the sts field. final sample time can be 2, 4, 8, or 16 adc clocks (see table 5-2 ). table 5-1 prescaler output prs[4:0] adc clock minimum system clock maximum system clock %00000 reserved %00001 system clock/4 2.0 mhz 8.4 mhz %00010 system clock/6 3.0 mhz 12.6 mhz %00011 system clock/8 4.0 mhz 16.8 mhz . . . . . . . . . . . . %11101 system clock/60 30.0 mhz %11110 system clock/62 31.0 mhz %11111 system clock/64 32.0 mhz system clock modulus counter divide by 2 adc clock pr[4:0] f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola digital control subsystem adc 5-4 reference manual 5.4 resolution adc resolution can be either eight or ten bits. resolution is determined by the state of the res10 bit in adctl0 (0 = 8-bit resolution, 1 = 10-bit resolution). both 8-bit and 10-bit conversion results are automatically aligned in the result registers. refer to 5.1 conversion timing for the time required for 8- and 10-bit conversions. 5.5 conversion mode conversion mode is controlled by three bits in adctl1. table 5-3 shows the meaning of these bits. the combination of these bits determines the conversion mode, as shown in table 5- 4 and explained in the following paragraphs. conversion begins with the multiplexer input specified by the value in the cd:ca field of adctl1. table 5-2 sts field selection sts[1:0] sample time 00 2 a/d clock periods 01 4 a/d clock periods 10 8 a/d clock periods 11 16 a/d clock periods table 5-3 conversion mode bits bit meaning scan (scan mode selection) conversion can be limited to a single sequence or performed continuously 0 = single sequence 1 = continuous conversions mult (multichannel conversions) conversion can be run on a single channel or on a block of four or eight channels (depending on s8cm) 0 = single channel 1 = multiple channels s8cm (select 8-conversion sequence mode) length of a conversion sequence 0 = 4 conversions 1 = 8 conversions table 5-4 adc conversion modes scan mult s8cm mode 000 0 001 1 010 2 011 3 100 4 101 5 110 6 111 7 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc digital control subsystem motorola reference manual 5-5 mode 0 ?a single 4-conversion sequence is performed on a single input channel specified by the value in cd:ca. each result is stored in a separate result register (rslt0 to rslt3). the appropriate ccf bit in adstat is set as each register is filled. the scf bit in adstat is set when the conversion sequence is com- plete. mode 1 ?a single 8-conversion sequence is performed on a single input channel specified by the value in cd:ca. each result is stored in a separate result register (rslt0 to rslt7). the appropriate ccf bit in adstat is set as each register is filled. the scf bit in adstat is set when the conversion sequence is com- plete. mode 2 ?a single conversion is performed on each of four sequential input chan- nels, starting with the channel specified by the value in cd:cc. each result is stored in a separate result register (rslt0 to rslt3). the appropriate ccf bit in adstat is set as each register is filled. the scf bit in adstat is set when the last conversion is complete. mode 3 ?a single conversion is performed on each of eight sequential input chan- nels, starting with the channel specified by the value in cd. each result is stored in a separate result register (rslt0 to rslt7). the appropriate ccf bit in ad- stat is set as each register is filled. the scf bit in adstat is set when the last conversion is complete. mode 4 ?continuous 4-conversion sequences are performed on a single input channel specified by the value in cd:ca. each result is stored in a separate re- sult register (rslt0 to rslt3). previous results are overwritten when a se- quence repeats. the appropriate ccf bit in adstat is set as each register is filled. the scf bit in adstat is set when the first 4-conversion sequence is complete. mode 5 ?continuous 8-conversion sequences are performed on a single input channel specified by the value in cd:ca. each result is stored in a separate re- sult register (rslt0 to rslt7). previous results are overwritten when a se- quence repeats. the appropriate ccf bit in adstat is set as each register is filled. the scf bit in adstat is set when the first 8-conversion sequence is complete. mode 6 ?continuous conversions are performed on each of four sequential input channels, starting with the channel specified by the value in cd:cc. each result is stored in a separate result register (rslt0 to rslt3). the appropriate ccf bit in adstat is set as each register is filled. the scf bit in adstat is set when the first 4-conversion sequence is complete. mode 7 ?continuous conversions are performed on each of eight sequential input channels, starting with the channel specified by the value in cd. each result is stored in a separate result register (rslt0 to rslt7). the appropriate ccf bit in adstat is set as each register is filled. the scf bit in adstat is set when the first 8-conversion sequence is complete. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola digital control subsystem adc 5-6 reference manual 5.6 channel selection the value of the channel selection field (cd:ca) in adctl1 determines which multi- plexer input or inputs are used in a conversion sequence. there are 16 possible in- puts. eight inputs are external pins (an[7:0]), and eight are internal. table 5-5 summarizes adc operation when mult is cleared (single-channel modes). table 5-6 summarizes adc operation when mult is set (multichannel modes). the scan bit determines whether single or continuous conversion sequences are per- formed. channel numbers are given in order of conversion. table 5-5 single-channel conversions s8cm cd cc cb ca input result register 0 0000 an0 rslt0 ?rslt3 0 0001 an1 rslt0 ?rslt3 0 0010 an2 rslt0 ?rslt3 0 0011 an3 rslt0 ?rslt3 0 0100 an4 rslt0 ?rslt3 0 0101 an5 rslt0 ?rslt3 0 0110 an6 rslt0 ?rslt3 0 0111 an7 rslt0 ?rslt3 0 1000 reserved rslt0 ?rslt3 0 1001 reserved rslt0 ?rslt3 0 1010 reserved rslt0 ?rslt3 0 1011 reserved rslt0 ?rslt3 0 1100 v rh rslt0 ?rslt3 0 1101 v rl rslt0 ?rslt3 0 1110 (v rh v rl ) / 2 rslt0 ?rslt3 0 1111 test/reserved rslt0 ?rslt3 1 0000 an0 rslt0 ?rslt7 1 0001 an1 rslt0 ?rslt7 1 0010 an2 rslt0 ?rslt7 1 0011 an3 rslt0 ?rslt7 1 0100 an4 rslt0 ?rslt7 1 0101 an5 rslt0 ?rslt7 1 0110 an6 rslt0 ?rslt7 1 0111 an7 rslt0 ?rslt7 1 1000 reserved rslt0 ?rslt7 1 1001 reserved rslt0 ?rslt7 1 1010 reserved rslt0 ?rslt7 1 1011 reserved rslt0 ?rslt7 1 1100 v rh rslt0 ?rslt7 1 1101 v rl rslt0 ?rslt7 1 1110 (v rh ?v rl ) / 2 rslt0 ?rslt7 1 1111 test/reserved rslt0 ?rslt7 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc digital control subsystem motorola reference manual 5-7 5.7 control and status registers there are two control registers and one status register. writes to adctl1 initiate a conversion. if a conversion sequence is already in progress, a write to either control register aborts it and resets the scf and ccf flags in adstat. 5.7.1 adc control register 0 (adctl0) adctl0 is used to select the conversion resolution (8 or 10 bits), the sample time, and the clock/prescaler value. writing to this register aborts any conversion in progress, and adc activity halts until a write to adctl1 occurs. table 5-6 multiple-channel conversions s8cm cd cc cb ca input result register 0 0 0 x x an0 rslt0 an1 rslt1 an2 rslt2 an3 rslt3 0 0 1 x x an4 rslt0 an5 rslt1 an6 rslt2 an7 rslt3 0 1 0 x x reserved rslt0 reserved rslt1 reserved rslt2 reserved rslt3 011xx v rh rslt0 v rl rslt1 (v rh ?v rl ) / 2 rslt2 test/reserved rslt3 1 0 x x x an0 rslt0 an1 rslt1 an2 rslt2 an3 rslt3 an4 rslt4 an5 rslt5 an6 rslt6 an7 rslt7 1 1 x x x reserved rslt0 reserved rslt1 reserved rslt2 reserved rslt3 v rh rslt4 v rl rslt5 (v rh v rl ) / 2 rslt6 test/reserved rslt7 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola digital control subsystem adc 5-8 reference manual res10 ?10-bit resolution 0 = 8-bit conversion 1 = 10-bit conversion sts[1:0] ?sample time select 00 = 2 a/d clock periods 01 = 4 a/d clock periods 10 = 8 a/d clock periods 11 = 16 a/d clock periods the sts field selects the final sample time, after the buffered sample transfer has oc- curred. refer to 5.1 conversion timing and 5.3 final sample time for additional in- formation. prs[4:0] ?prescaler rate selection %00000 = system clock/4 %00001 = system clock/4 %00010 = system clock/6 %00011 = system clock/8 .. .. . . %11101 = system clock/60 %11110 = system clock/62 %11111 = system clock/64 the system clock is divided by the prs value plus one, then divided by two, to deter- mine the adc clock. (assigning a value of zero to this field, however, has the same effect as assigning a value of one.) refer to 5.2 clock and prescaler control for more information. 5.7.2 adc control register 1 (adctl1) adctl1 is used to select the conversion mode and the channel or channels to be con- verted. writing to this register aborts any conversion in progress and initiates a new conversion. refer to 5.5 conversion mode and 5.6 channel selection for additional information on these fields. scan ?scan mode selection 0 = single conversion sequence 1 = continuous conversion adctl0 ?adc control register 0 $xxxx0a 15 8 7 6 5 4 3 2 1 0 not used res10 sts prs reset: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 adctl1 ?adc control register 1 $xxxx0c 15 8 7 6 5 4 3 2 1 0 not used scan mult s8cm cd cc cb ca reset: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc digital control subsystem motorola reference manual 5-9 mult ?multichannel conversion 0 = conversion sequence(s) run on a channel selected by cd:ca. 1 = sequential conversion of four or eight channels selected by cd:ca. s8cm ?select eight-conversion sequence mode 0 = four-conversion sequence 1 = eight-conversion sequence cd:ca ?channel selection the bits in this field are used to select an input or block of inputs for a/d conversion. table 5-5 and table 5-6 explain the operation of these fields. 5.7.3 adc status register (adstat) adstat is a read-only register that contains the sequence complete flag (scf), con- version counter (cctr), and one channel converted flag (ccf) for each of the eight channels. scf ?sequence complete flag this bit is set at the end of the conversion sequence when scan = 0 in adctl1 and set at the end of the first conversion sequence when scan = 1. 0 = sequence not complete 1 = sequence complete cctr[2:0] ?conversion counter this field shows the content of the conversion counter pointer during a conversion se- quence. the value is the number of the next result register to be written to (i.e., the channel currently being converted). ccf[7:0] ?conversion complete flags each bit in this field corresponds to an a/d result register (ccf7 corresponds to rslt7, etc.). a bit is set when conversion of the corresponding input is complete and is cleared when the result register containing the converted value is read. 5.8 result registers (rslt0?slt7) the eight read-only result registers store data after conversion is complete. each reg- ister can be read from three different addresses in the register block. data format de- pends on the address from which it is read. the result registers reside on the internal differential data bus. adstat ?adc status register $xxxx0e 15 14 11 10 8 7 0 scf not used cctr ccf reset: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola digital control subsystem adc 5-10 reference manual the conversion result is unsigned right-justified data. bits [9:0] are used for 10-bit res- olution, bits [7:0] are used for 8-bit resolution (bits [9:8] are zero). bits [15:10] always return zero when read. the conversion result is signed left-justified data. bits [15:6] are used for 10-bit reso- lution, bits [15:8] are used for 8-bit resolution (bits [7:6] are zero). although the adc is a unipolar converter, this data format is provided by assuming that the zero reference point is (v rh + v rl ) / 2. when the register is read, bit 15 re- turns zero for a positive number and one for a negative number. for a negative num- ber, the value read is in twos complement form. bits [5:0] return zeros when read. for eight-bit conversions, the table below summarizes the results of a read of the upper byte of this register. the conversion result is unsigned left-justified data. bits [15:6] are used for 10-bit res- olution, bits [15:8] are used for 8-bit resolution (bits [7:6] are zero). bits [5:0] always return zero when read. unsigned right-justified format $xxxx10?xxxx1f 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 not used 10-bit result 8/10-bit result signed left-justified format $xxxx20?xxxx2f 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 8/10-bit result 10-bit result not used input voltage digital result + full scale (v rh ) $7f bipolar zero ((v rh - v rh )/2) $00 zero - 1 count $ff ?full scale (v rl ) $80 unsigned left-justified format $xxxx30?xxxx3f 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 8/10-bit result 10-bit result not used f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc pin connection considerations motorola reference manual 6-1 section 6 pin connection considerations the adc requires accurate, noise-free input signals for proper operation. this section discusses the design of external circuitry to maximize adc performance. 6.1 analog reference pins no a/d converter can be more accurate than its analog reference. any noise in the reference can result in at least that much error in a conversion. the reference for the adc, supplied by pins v rh and v rl , should be low-pass filtered from its source to ob- tain a noise-free, clean signal. in many cases, simple capacitive bypassing may suf- fice. in extreme cases, inductors or ferrite beads may be necessary if noise or rf energy is present. series resistance is not advisable since there is an effective dc cur- rent requirement from the reference voltage by the internal resistor string in the rc dac array. external resistance may introduce error in this architecture under certain conditions. any series devices in the filter network should contain a minimum amount of dc resistance. for accurate conversion results, the analog reference voltages must be within the lim- its defined by v dda and v ssa , as explained in the following subsection. 6.2 analog power pins the analog supply pins (v dda and v ssa ) define the limits of the analog reference volt- ages (v rh and v rl ) and of the analog multiplexer inputs. figure 6-1 is a diagram of the analog input circuitry. figure 6-1 analog input circuitry sample amp 8 channels total rc dac array comparator ref 1 v ssa v rl ref 2 v dda v rh f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola pin connection considerations adc 6-2 reference manual since the sample amplifier is powered by v dda and v ssa , it can accurately transfer input signal levels up to but not exceeding v dda and down to but not below v ssa . if the input signal is outside of this range, the output from the sample amplifier is clipped. in addition, v rh and v rl must be within the range defined by v dda and v ssa . as long as v rh is less than or equal to v dda and v rl is greater than or equal to v ssa and the sample amplifier has accurately transferred the input signal, resolution is rati- ometric within the limits defined by v rl and v rh . if v rh is greater than v dda , the sample amplifier can never transfer a full-scale value. if v rl is less than v ssa , the sample amplifier can never transfer a zero value. figure 6-2 shows the results of reference voltages outside the range defined by v dda and v ssa . at the top of the input signal range, v dda is 10 mv lower than v rh . this results in a maximum obtainable 10-bit conversion value of 3fe. at the bottom of the signal range, v ssa is 15 mv higher than v rl, resulting in a minimum obtainable 10- bit conversion value of 3. figure 6-2 errors resulting from clipping 6.3 analog input pins analog inputs should have low ac impedance at the pins. low ac impedance can be realized by placing a capacitor with good high frequency characteristics at the input pin of the part. ideally, that capacitor should be as large as possible (within the practi- 0 .020 5.100 5.110 input in volts (v rh = 5.120 v, v rl = 0 v) 1 2 3 4 5 6 7 8 3fa 3fb 3fc 3fd 3fe 3ff .010 .030 5.120 5.130 10-bit result 5.140 0 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc pin connection considerations motorola reference manual 6-3 cal range of capacitors that still have good high frequency characteristics). this capac- itor has two effects. first, it helps attenuate any noise that may exist on the input. second, it sources charge during the sample period when the analog signal source is a high-impedance source. series resistance can be used with the capacitor on an input pin to implement a simple rc filter. the maximum level of filtering at the input pins is application dependent and is based on the bandpass characteristics required to accurately track the dynamic characteristics of an input. simple rc filtering at the pin may be limited by the source impedance of the transducer or circuit supplying the analog signal to be measured. (refer to 6.3.2 error resulting from leakage .) in some cases, the size of the capac- itor at the pin may be very small. figure 6-3 is a simplified model of an input channel. refer to this model in the follow- ing discussion of the interaction between the user's external circuitry and the circuitry inside the adc. figure 6-3 electrical model of an a/d input pin in figure 6-3 , r f and c f comprise the user's external filter circuit. c s is the internal sample capacitor. the value for this capacitor is 2 pf. each channel has its own ca- pacitor. the 2-pf capacitor is never precharged: it retains the value of the last sample. v i is an internal voltage source used to precharge the dac capacitor array (c dac ) be- fore each sample. the value of this supply is v dd /2, or 2.5 volts for 5-volt operation. the following paragraphs provide a simplified description of the interaction between the adc and the user's external circuitry. this circuitry is assumed to be a simple rc low-pass filter passing a signal from a source to the adc input pin. the following sim- plifying assumptions are made: s1 s2 amp r f s4 s3 c dac v i c s c f v src internal circuit model external circuit = source voltage = internal capacitance (for a bypassed channel, this is the c dac capacitance) v src r f c f c s c dac v i = filter impedance (source impedance included) = filter capacitor = dac capacitor array = internal voltage source for precharge (v dd /2) f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola pin connection considerations adc 6-4 reference manual ?the source impedance is included with the series resistor of the rc filter. ?the external capacitor is perfect (no leakage, no significant dielectric absorption characteristics, etc.) ?all parasitic capacitance associated with the input pin is included in the value of the external capacitor. ?inductance is ignored. ?the ?n?resistance of the internal switches is zero ohms and the ?ff?resistance is infinite. 6.3.1 settling time for the external circuit the values for r f and c f in the user's external circuitry determine the length of time required to charge c f to the source voltage level (v src ). at time t = 0, s1 in figure 6-3 closes. s2 is open, disconnecting the internal circuitry from the external circuitry. assume that the initial voltage across c f is 0. as c f charges, the voltage across it is determined by the following equation, where t is the total charge time: v cf = v src (1? ?/r f c f) when t = 0, the voltage across c f = 0. as t approaches infinity, v cf will equal v src . (this assumes no internal leakage.) with 10-bit resolution, 1/2 of a count is equal to 1/2048 full-scale value. assuming worst case (v src = full scale), table 6-1 shows the required time for c f to charge to within 1/2 of a count of the actual source voltage dur- ing 10-bit conversions. note that these times are completely independent of the a/d converter architecture (assuming the adc is not affecting the charging). the external circuit described in table 6-1 is a low-pass filter. a user interested in measuring an ac component of the external signal must take the characteristics of this filter into account. 6.3.2 error resulting from leakage a series resistor can limit the current to a pin, but input leakage acting through a large source impedance can degrade a/d accuracy. the maximum input leakage current is specified in appendix a electrical characteristics . input leakage is greatest at high operating temperatures and as a general rule decreased by one half for each 10 c decrease in temperature. when v rh ?v rl = 5.12 v, 1 count (assuming 10-bit resolution) corresponds to 5 mv of input voltage. a typical input leakage of 50 na acting through 100 k w of external se- table 6-1 external circuit settling time (10-bit conversions) filter source resistance capacitor 100 w 1 k w 10 k w 100 k w 1 m f 760 m s 7.6 ms 76 ms 760 ms .1 m f 76 m s 760 m s 7.6 ms 76 ms .01 m f 7.6 m s 76 m s 760 m s 7.6 ms .001 m f 760 ns 7.6 m s 76 m s 760 m s 100 pf 76 ns 760 ns 7.6 m s 76 m s f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc pin connection considerations motorola reference manual 6-5 ries resistance results in an error of less than 1 count (5.0 mv). if the source imped- ance is 1 m w and a typical leakage of 50 na is present, an error of 10 counts (50 mv) is introduced. in addition to internal junction leakage, external leakage (e.g., if external clamping di- odes are used) and charge sharing effects with internal capacitors also contribute to the total leakage current. table 6-2 illustrates the effect of different levels of total leak- age on accuracy for different values of source impedance. the error is listed in terms of 10-bit counts. notice that leakage from the part of 10 na is obtainable only within a limited temperature range. table 6-2 error resulting from input leakage (i off ) source leakage value (10-bit conversions) impedance 10 na 50 na 100 na 1000 na 1 k w 0.2 counts 10 k w 0.1 counts 0.2 counts 2 counts 100 k w 0.2 counts 1 count 2 counts 20 counts f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola pin connection considerations adc 6-6 reference manual f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc electrical characteristics motorola reference manual a-1 appendix a electrical characteristics the following ratings define the conditions under which the adc can operate without damage. notes: 1. below disruptive current conditions, the channel being stressed will have conversion values of $3ff for analog inputs greater than v rh and $000 for values less than v rl . this assumes that v rh v dda and v rl 3 v ssa due to the presence of the sample amplifier. other channels are not affected by non- disruptive conditions 2. input signals with large slew rates or high frequency noise components cannot be converted accu- rately. these signals also interfere with conversion of other channels. table a-1 maximum ratings num parameter symbol min max unit 1 analog supply v dda ?0.3 6.5 v 2 internal digital supply v ddi ?0.3 6.5 v 3 reference supply v rh , v rl ?0.3 6.5 v 4v ss differential voltage v ssi ? v ssa ?0.1 0.1 v 5v dd differential voltage v ddi ? v dda ?6.5 6.5 v 6v ref differential voltage v rh ? v rl ?6.5 6.5 v 7v ref to v dda differential voltage v rh ? v dda ?6.5 6.5 v 8 disruptive input current 1,2 i na ?15 15 m a f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola electrical characteristics adc a-2 reference manual notes: 1. refers to operation over full temperature and frequency range. 2. to obtain full-scale, full-range results, v ssa v rl v indc v rh v dda. 3. current measured at maximum system clock frequency with all modules active. 4. maximum leakage occurs at maximum operating temperature. as a general rule, current decreases by half for each 10 c below maximum temperature notes: 1. assumes 2.1 mhz adc clock and selection of minimum sample time (2 adc clocks) table a-2 adc dc electrical characteristics (operating) (vss = 0 vdc, adclk = 2.1 mhz, ta within operating temperature range) num parameter symbol min max unit 1 analog supply 1 v dda 4.5 5.5 v 2 internal digital supply 1 v ddi 4.5 5.5 v 3v ss differential voltage v ssi ? v ssa ?1.0 1.0 mv 4v dd differential voltage v ddi ? v dda ?1.0 1.0 v 5 reference voltage low 2 v rl v ssa v dda / 2 v 6 reference voltage high 2 v rh v dda / 2 v dda v 7v ref differential voltage v rh ? v rl 4.5 5.5 v 8 input voltage 2 v indc v ssa v dda v 9 input high, digital port v ih 0.7 (v dda )v dda + 0.3 v 10 input low, digital port v il v ssa ?0.3 0.2 (v dda )v 11 cmos output high, digital port i oh = ?10.0 m a v oh v dda ?0.2 v 12 output low, digital port i ol = 10.0 m a v ol 0.2 v 13 output high, digital port i oh = ?0.8 ma v oh v dda ?0.8 v 14 output low, digital port i ol = 1.6 ma v ol 0.4 v 15 analog supply current 3 i dda 1.0 ma 17 reference supply current i ref 250 m a 18 input current, off channel 4 i off 100 na 19 total input capacitance, not sampling c inn ?0 pf 20 total input capacitance, sampling c ins ?5 pf table a-3 adc ac characteristics (operating) (vdd and vdda = 5.0 vdc 10%, vss = 0 vdc, ta within operating temperature range) num parameter symbol min max unit 1 imb clock frequency f iclk 2.0 16.78 mhz 2 adc clock frequency f adclk 0.5 2.1 mhz 3 8-bit conversion time (16 adc clocks) 1 t conv 7.62 m s 4 10-bit conversion time (18 adc clocks) 1 t conv 8.58 m s 5 stop recovery time t sr ?0 m s f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc electrical characteristics motorola reference manual a-3 notes: 1. v rh ?v rl 3 5.12 v; v dda - v ssa = 5.12 v 2. at v ref = 5.12 v, one 10-bit count = 5 mv and one 8-bit count = 20 mv. 3. 8-bit absolute error of 1 count (20 mv) includes 1/2 count (10 mv) inherent quantization error and 1/2 count (10 mv) circuit (differential, integral, and offset) error. 4. 10-bit absolute error of 2.5 counts (12.5 mv) includes 1/2 count (2.5 mv) inherent quantization error and 2 counts (10 mv) circuit (differential, integral, and offset) error. 5. maximum source impedance is application-dependent. error resulting from pin leakage depends on junction leakage into the pin and on charge-sharing effects with internal capacitors. error from junction leakage is a func- tion of source impedance and input leakage current: v err = r s i off where i off is a function of operating temperature. (see note 4 in table a?.) charge-sharing effects with internal capacitors are a function of adc clock speed, the number of channels being scanned, and source impedance. for 10-bit conversions, charge pump leakage is computed as follows: v err10 = .25 pf v dda r s adclk/(9 number of channels) for 8-bit conversions, charge pump leakage is computed as follows: v err8 = .25 pf v dda r s adclk/(8 number of channels) table a-4 analog converter characteristics (operating) (vdd and vdda = 5.0 vdc 10%, vss = 0 vdc, ta = tl to th, adclk = 2.1 mhz) num parameter symbol min typ max unit 1 8-bit resolution 1 1 count 20 mv 2 8-bit differential nonlinearity 2 dnl ?.5 0.5 counts 3 8-bit integral nonlinearity 2 inl ? 1 counts 4 8-bit absolute error 2,3 ae ? 1 counts 5 10-bit resolution 1 1 count 5 mv 6 10-bit differential nonlinearity 2 dnl ?.5 0.5 counts 7 10-bit integral nonlinearity 2 inl ? 2 counts 8 10-bit absolute error 2,4 ae ?.5 2.5 counts 9 source impedance at input 5 r s 20 see note 5 k w f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola electrical characteristics adc a-4 reference manual figure a-1 circuit and quantization error in 8-bit conversions 0 204060 input in mv, v rh ?v rl = 5.120 v digital output a b c ?+1/2-count (10 mv) inherent quantization error ?circuit-contributed +10 mv error ?+20 mv absolute error (one 8-bit count) +20 mv 8-bit absolute error boundary 80 ?0 mv 8-bit absolute error boundary 8-bit transfer curve (no circuit error) ideal transfer curve a b c f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc electrical characteristics motorola reference manual a-5 figure a-2 circuit and quantization error in 10-bit conversions 0 204060 input in mv, v rh ?v rl = 5.120 v c a b digital output a b c ?+1/2-count (2.5 mv) inherent quantization error ?circuit-contributed +10 mv error ?+12.5 mv absolute error (2-1/2 10-bit counts) +12.5 mv 10-bit absolute error boundary ?2.5 mv 10-bit absolute error boundary 10-bit transfer curve (no circuit error) ideal transfer curve 80 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola electrical characteristics adc a-6 reference manual f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc memory map and registers motorola reference manual b-1 appendix b memory map and registers b.1 memory map s = supervisor-accessible only s/u = supervisor- or user-accessible depending on state of the supv bit in the adcmcr address access control registers $xxxx00 s module configuration register (adcmcr) $xxxx02 s adc test register (adctest) $xxxx04 s (reserved) $xxxx06 s/u port data register (pdr) $xxxx08 s/u (reserved) $xxxx0a s/u adc control register 0 (adctl0) $xxxx0c s/u adc control register 1 (adctl1) $xxxx0e s/u adc status register (adstat) address access right-justified unsigned result registers $xxxx10 s/u adc result register 0 (rslt0) $xxxx12 s/u adc result register 1 (rslt1) $xxxx14 s/u adc result register 2 (rslt2) $xxxx16 s/u adc result register 3 (rslt3) $xxxx18 s/u adc result register 4 (rslt4) $xxxx1a s/u adc result register 5 (rslt5) $xxxx1c s/u adc result register 6 (rslt6) $xxxx1e s/u adc result register 7 (rslt7) address access left-justified signed result registers $xxxx20 s/u adc result register 0 (rslt0) $xxxx22 s/u adc result register 1 (rslt1) $xxxx24 s/u adc result register 2 (rslt2) $xxxx26 s/u adc result register 3 (rslt3) $xxxx28 s/u adc result register 4 (rslt4) $xxxx2a s/u adc result register 5 (rslt5) $xxxx2c s/u adc result register 6 (rslt6) $xxxx2e s/u adc result register 7 (rslt7) address access left-justified unsigned result registers $xxxx30 s/u adc result register 0 (rslt0) $xxxx32 s/u adc result register 1 (rslt1) $xxxx34 s/u adc result register 2 (rslt2) $xxxx36 s/u adc result register 3 (rslt3) $xxxx38 s/u adc result register 4 (rslt4) $xxxx3a s/u adc result register 5 (rslt5) $xxxx3c s/u adc result register 6 (rslt6) $xxxx3e s/u adc result register 7 (rslt7) f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola memory map and registers adc b-2 reference manual b.2 registers stop ?stop mode 0 = normal operation 1 = low-power operation frz[1:0] ?freeze the frz field determines adc response to assertion of the freeze signal by the cpu. 00 = ignore freeze 01 = reserved 10 = finish conversion, then freeze 11 = freeze immediately supv ?supervisor/unrestricted 0 = unrestricted access to registers controlled by the supv bit 1 = supervisor access only res10 ?10-bit resolution 0 = 8-bit conversion 1 = 10-bit conversion sts[1:0] ?sample time select field the sts field selects the initial sample time. 00 = 2 a/d clock periods 01 = 4 a/d clock periods 10 = 8 a/d clock periods 11 = 16 a/d clock periods refer to 5.1 conversion timing and 5.3 final sample time for additional informa- tion. adcmcr ?adc module configuration register $xxxx00 15 14 13 12 8 7 6 0 stop frz not used supv not used reset: 1 0 0 0 pdr ?port data register $xxxx06 15 8 7 0 port adb output data port ada input data reset: 0 0 0 0 0 0 0 0 state of input pins adctl0 ?adc control register 0 $xxxx0a 15 8 7 6 5 4 3 2 1 0 not used res10 sts prs reset: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . adc memory map and registers motorola reference manual b-3 prs[4:0] ?prescaler rate selection field %00000 = system clock/4 %00001 = system clock/4 %00010 = system clock/6 %00011 = system clock/8 . . . . . . %11101 = system clock/60 %11110 = system clock/62 %11111 = system clock/64 the system clock is divided by the prs value plus one, then divided by two, to deter- mine the adc clock. (assigning a value of zero to this field, however, has the same effect as assigning a value of one.) refer to 5.2 clock and prescaler control for more information. scan ?scan mode selection bit 0 = single conversion sequence 1 = continuous conversion mult ?multichannel conversion bit 0 = conversion sequence(s) run on a channel selected by [cd:ca]. 1 = sequential conversion of four or eight channels selected by [cd:ca]. s8cm ?select eight-conversion sequence mode 0 = four-conversion sequence 1 = eight-conversion sequence cd:ca ?channel selection the bits in this field are used to select an input or block of inputs for a/d conversion. table 5-5 and table 5-6 explain the operation of these fields. scf ?sequence complete flag this bit is set at the end of the conversion sequence when scan = 0 in adctl1 and set at the end of the first conversion sequence when scan = 1. 0 = sequence not complete 1 = sequence complete adctl1 ?adc control register 1 $xxxx0c 15 8 7 6 5 4 3 2 1 0 not used scan mult s8cm cd cc cb ca reset: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 adstat ?adc status register $xxxx0e 15 14 11 10 8 7 0 scf not used cctr ccf reset: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . motorola memory map and registers adc b-4 reference manual cctr[2:0] ?conversion counter this field shows the content of the conversion counter pointer during a conversion se- quence. the value is the number of the next result register to be written to (i.e., the channel currently being converted). ccf[7:0] ?conversion complete each bit in this field corresponds to an a/d result register (ccf7 corresponds to rslt7, etc.). a bit is set when conversion of the corresponding input is complete and is cleared when the result register containing the converted value is read. the conversion result is unsigned right-justified data. bits [9:0] are used for 10-bit res- olution, bits [7:0] are used for 8-bit conversion (bits [9:8] are zero). bits [15:10] always return zero when read. the conversion result is signed left-justified data. bits [15:6] are used for 10-bit reso- lution, bits [15:8] are used for 8-bit conversion (bits [7:6] are zero). although the adc is a unipolar converter, this data format is provided by assuming that the zero refer- ence point is (v rh - v rl ) / 2. a read of bit 15 returns the inverse of the stored value and indicates the sign of the result. the value read from this register is thus an offset binary twos complement number. bits [5:0] return zero when read. the conversion result is unsigned left-justified data. bits [15:6] are used for 10-bit res- olution, bits [15:8] are used for 8-bit conversion (bits [7:6] are zero). bits [5:0] always return zero when read. rslt0?slt7 ?result registers (right-justified) $xxxx10?xxxx1f 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 not used 10-bit result 8/10-bit result rslt0?slt7 ?result registers (signed left-justified) $xxxx20?xxxx2f 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 8/10-bit result 10-bit result not used rslt0?slt7 ?result registers (unsigned left-justified) $xxxx30?xxxx3f 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 8/10-bit result 10-bit result not used f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . . |
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