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october 1994 order number: 231244-006 82C54 chmos programmable interval timer y compatible with all intel and most other microprocessors y high speed, ``zero wait state'' operation with 8 mhz 8086/88 and 80186/188 y handles inputs from dc e 10 mhz for 82C54-2 y available in express e standard temperature range e extended temperature range y three independent 16-bit counters y low power chmos ei cc e 10 ma @ 8 mhz count frequency y completely ttl compatible y six programmable counter modes y binary or bcd counting y status read back command y available in 24-pin dip and 28-pin plcc the intel 82C54 is a high-performance, chmos version of the industry standard 8254 counter/timer which is designed to solve the timing control problems common in microcomputer system design. it provides three independent 16-bit counters, each capable of handling clock inputs up to 10 mhz. all modes are software programmable. the 82C54 is pin compatible with the hmos 8254, and is a superset of the 8253. six programmable timer modes allow the 82C54 to be used as an event counter, elapsed time indicator, programmable one-shot, and in many other applications. the 82C54 is fabricated on intel's advanced chmos iii technology which provides low power consumption with performance equal to or greater than the equivalent hmos product. the 82C54 is available in 24-pin dip and 28-pin plastic leaded chip carrier (plcc) packages. 231244 1 figure 1. 82C54 block diagram 231244 3 plastic leaded chip carrier 231244 2 diagrams are for pin reference only. package sizes are not to scale. figure 2. 82C54 pinout
82C54 table 1. pin description symbol pin number type function dip plcc d 7 -d 0 1-8 2-9 i/o data: bidirectional tri-state data bus lines, connected to system data bus. clk 0 9 10 i clock 0: clock input of counter 0. out 0 10 12 o output 0: output of counter 0. gate 0 11 13 i gate 0: gate input of counter 0. gnd 12 14 ground: power supply connection. out 1 13 16 o out 1: output of counter 1. gate 1 14 17 i gate 1: gate input of counter 1. clk 1 15 18 i clock 1: clock input of counter 1. gate 2 16 19 i gate 2: gate input of counter 2. out 2 17 20 o out 2: output of counter 2. clk 2 18 21 i clock 2: clock input of counter 2. a 1 ,a 0 20-19 23-22 i address: used to select one of the three counters or the control word register for read or write operations. normally connected to the system address bus. a 1 a 0 selects 0 0 counter 0 0 1 counter 1 1 0 counter 2 1 1 control word register cs 21 24 i chip select: a low on this input enables the 82C54 to respond to rd and wr signals. rd and wr are ignored otherwise. rd 22 26 i read control: this input is low during cpu read operations. wr 23 27 i write control: this input is low during cpu write operations. v cc 24 28 power: a 5v power supply connection. nc 1, 11, 15, 25 no connect functional description general the 82C54 is a programmable interval timer/counter designed for use with intel microcomputer systems. it is a general purpose, multi-timing element that can be treated as an array of i/o ports in the system software. the 82C54 solves one of the most common prob- lems in any microcomputer system, the generation of accurate time delays under software control. in- stead of setting up timing loops in software, the pro- grammer configures the 82C54 to match his require- ments and programs one of the counters for the de- sired delay. after the desired delay, the 82C54 will interrupt the cpu. software overhead is minimal and variable length delays can easily be accommodated. some of the other counter/timer functions common to microcomputers which can be implemented with the 82C54 are: # real time clock # even counter # digital one-shot # programmable rate generator # square wave generator # binary rate multiplier # complex waveform generator # complex motor controller 2
82C54 block diagram data bus buffer this 3-state, bi-directional, 8-bit buffer is used to in- terface the 82C54 to the system bus (see figure 3). 231244 4 figure 3. block diagram showing data bus buffer and read/write logic functions read/write logic the read/write logic accepts inputs from the sys- tem bus and generates control signals for the other functional blocks of the 82C54. a 1 and a 0 select one of the three counters or the control word regis- ter to be read from/written into. a ``low'' on the rd input tells the 82C54 that the cpu is reading one of the counters. a ``low'' on the wr input tells the 82C54 that the cpu is writing either a control word or an initial count. both rd and wr are qualified by cs ;rd and wr are ignored unless the 82C54 has been selected by holding cs low. the wr y and clk signals should be synchronous. this is accomplished by using a clk input signal to the 82C54 counters which is a derivative of the sys- tem clock source. another technique is to externally synchronize the wr y and clk input signals. this is done by gating wr y with clk. control word register the control word register (see figure 4) is selected by the read/write logic when a 1 ,a 0 e 11. if the cpu then does a write operation to the 82C54, the data is stored in the control word register and is interpreted as a control word used to define the operation of the counters. the control word register can only be written to; status information is available with the read-back command. 231244 5 figure 4. block diagram showing control word register and counter functions counter 0, counter 1, counter 2 these three functional blocks are identical in opera- tion, so only a single counter will be described. the internal block diagram of a single counter is shown in figure 5. the counters are fully independent. each counter may operate in a different mode. the control word register is shown in the figure; it is not part of the counter itself, but its contents de- termine how the counter operates. 3
82C54 231244 6 figure 5. internal block diagram of a counter the status register, shown in the figure, when latched, contains the current contents of the control word register and status of the output and null count flag. (see detailed explanation of the read- back command.) the actual counter is labelled ce (for ``counting ele- ment''). it is a 16-bit presettable synchronous down counter. ol m and ol l are two 8-bit latches. ol stands for ``output latch''; the subscripts m and l stand for ``most significant byte'' and ``least significant byte'' respectively. both are normally referred to as one unit and called just ol. these latches normally ``fol- low'' the ce, but if a suitable counter latch com- mand is sent to the 82C54, the latches ``latch'' the present count until read by the cpu and then return to ``following'' the ce. one latch at a time is enabled by the counter's control logic to drive the internal bus. this is how the 16-bit counter communicates over the 8-bit internal bus. note that the ce itself cannot be read; whenever you read the count, it is the ol that is being read. similarly, there are two 8-bit registers called cr m and cr l (for ``count register''). both are normally referred to as one unit and called just cr. when a new count is written to the counter, the count is stored in the cr and later transferred to the ce. the control logic allows one register at a time to be loaded from the internal bus. both bytes are trans- ferred to the ce simultaneously. cr m and cr l are cleared when the counter is programmed. in this way, if the counter has been programmed for one byte counts (either most significant byte only or least significant byte only) the other byte will be zero. note that the ce cannot be written into; whenever a count is written, it is written into the cr. the control logic is also shown in the diagram. clk n, gate n, and out n are all connected to the out- side world through the control logic. 82C54 system interface the 82C54 is treated by the systems software as an array of peripheral i/o ports; three are counters and the fourth is a control register for mode program- ming. basically, the select inputs a 0 ,a 1 connect to the a 0 , a 1 address bus signals of the cpu. the cs can be derived directly from the address bus using a linear select method. or it can be connected to the output of a decoder, such as an intel 8205 for larger sys- tems. 231244 7 figure 6. 82C54 system interface 4
82C54 operational description general after power-up, the state of the 82C54 is undefined. the mode, count value, and output of all counters are undefined. how each counter operates is determined when it is programmed. each counter must be programmed before it can be used. unused counters need not be programmed. programming the 82C54 counters are programmed by writing a control word and then an initial count. the control word format is shown in figure 7. all control words are written into the control word register, which is selected when a 1 ,a 0 e 11. the control word itself specifies which counter is being programmed. by contrast, initial counts are written into the coun- ters, not the control word register. the a 1 ,a 0 in- puts are used to select the counter to be written into. the format of the initial count is determined by the control word used. control word format a 1 ,a 0 e 11 cs e 0rd e 1wr e 0 d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 sc1 sc0 rw1 rw0 m2 m1 m0 bcd sc e select counter: sc1 sc0 0 0 select counter 0 0 1 select counter 1 1 0 select counter 2 11 read-back command (see read operations) rw e read/write: rw1 rw0 0 0 counter latch command (see read operations) 0 1 read/write least significant byte only. 1 0 read/write most significant byte only. 1 1 read/write least significant byte first, then most significant byte. note: don't care bits (x) should be 0 to insure compatibility with future intel products. m e mode: m2 m1 m0 0 0 0 mode 0 0 0 1 mode 1 x 1 0 mode 2 x 1 1 mode 3 1 0 0 mode 4 1 0 1 mode 5 bcd: 0 binary counter 16-bits 1 binary coded decimal (bcd) counter (4 decades) figure 7. control word format 5
82C54 write operations the programming procedure for the 82C54 is very flexible. only two conventions need to be remem- bered: 1) for each counter, the control word must be written before the initial count is written. 2) the initial count must follow the count format specified in the control word (least significant byte only, most significant byte only, or least sig- nificant byte and then most significant byte). since the control word register and the three counters have separate addresses (selected by the a 1 ,a 0 inputs), and each control word specifies the counter it applies to (sc0, sc1 bits), no special in- struction sequence is required. any programming sequence that follows the conventions above is ac- ceptable. a new initial count may be written to a counter at any time without affecting the counter's pro- grammed mode in any way. counting will be affected as described in the mode definitions. the new count must follow the programmed count format. if a counter is programmed to read/write two-byte counts, the following precaution applies: a program must not transfer control between writing the first and second byte to another routine which also writes into that same counter. otherwise, the counter will be loaded with an incorrect count. a 1 a 0 control word e counter 0 1 1 lsb of count e counter 0 0 0 msb of count e counter 0 0 0 control word e counter 1 1 1 lsb of count e counter 1 0 1 msb of count e counter 1 0 1 control word e counter 2 1 1 lsb of count e counter 2 1 0 msb of count e counter 2 1 0 a 1 a 0 control word e counter 0 1 1 counter word e counter 1 1 1 control word e counter 2 1 1 lsb of count e counter 2 1 0 lsb of count e counter 1 0 1 lsb of count e counter 0 0 0 msb of count e counter 0 0 0 msb of count e counter 1 0 1 msb of count e counter 2 1 0 a 1 a 0 control word e counter 2 1 1 control word e counter 1 1 1 control word e counter 0 1 1 lsb of count e counter 2 1 0 msb of count e counter 2 1 0 lsb of count e counter 1 0 1 msb of count e counter 1 0 1 lsb of count e counter 0 0 0 msb of count e counter 0 0 0 a 1 a 0 control word e counter 1 1 1 control word e counter 0 1 1 lsb of count e counter 1 0 1 control word e counter 2 1 1 lsb of count e counter 0 0 0 msb of count e counter 1 0 1 lsb of count e counter 2 1 0 msb of count e counter 0 0 0 msb of count e counter 2 1 0 note: in all four examples, all counters are programmed to read/write two-byte counts. these are only four of many possible programming sequences. figure 8. a few possible programming sequences read operations it is often desirable to read the value of a counter without disturbing the count in progress. this is easi- ly done in the 82C54. there are three possible methods for reading the counters: a simple read operation, the counter latch command, and the read-back command. each is explained below. the first method is to per- form a simple read operation. to read the counter, which is selected with the a1, a0 inputs, the clk input of the selected counter must be inhibited by using either the gate input or external logic. other- wise, the count may be in the process of changing when it is read, giving an undefined result. 6
82C54 counter latch command the second method uses the ``counter latch com- mand''. like a control word, this command is written to the control word register, which is selected when a 1 ,a 0 e 11. also like a control word, the sc0, sc1 bits select one of the three counters, but two other bits, d5 and d4, distinguish this command from a control word. a 1 ,a 0 e 11; cs e 0; rd e 1; wr e 0 d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 sc1 sc0 0 0 x x x x sc1, sc0 - specify counter to be latched sc1 sc0 counter 00 0 01 1 10 2 1 1 read-back command d5,d4 - 00 designates counter latch command x - don't care note: don't care bits (x) should be 0 to insure compatibility with future intel products. figure 9. counter latching command format the selected counter's output latch (ol) latches the count at the time the counter latch command is received. this count is held in the latch until it is read by the cpu (or until the counter is reprogrammed). the count is then unlatched automatically and the ol returns to ``following'' the counting element (ce). this allows reading the contents of the counters ``on the fly'' without affecting counting in progress. multiple counter latch commands may be used to latch more than one counter. each latched coun- ter's ol holds its count until it is read. counter latch commands do not affect the programmed mode of the counter in any way. if a counter is latched and then, some time later, latched again before the count is read, the second counter latch command is ignored. the count read will be the count at the time the first counter latch command was issued. with either method, the count must be read accord- ing to the programmed format; specifically, if the counter is programmed for two byte counts, two bytes must be read. the two bytes do not have to be read one right after the other; read or write or pro- gramming operations of other counters may be in- serted between them. another feature of the 82C54 is that reads and writes of the same counter may be interleaved; for example, if the counter is programmed for two byte counts, the following sequence is valid. 1. read least significant byte. 2. write new least significant byte. 3. read most significant byte. 4. write new most significant byte. if a counter is programmed to read/write two-byte counts, the following precaution applies; a program must not transfer control between reading the first and second byte to another routine which also reads from that same counter. otherwise, an incorrect count will be read. read-back command the third method uses the read-back command. this command allows the user to check the count value, programmed mode, and current state of the out pin and null count flag of the selected coun- ter(s). the command is written into the control word reg- ister and has the format shown in figure 10. the command applies to the counters selected by set- ting their corresponding bits d3,d2,d1 e 1. a0, a1 e 11 cs e 0rd e 1wr e 0 d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 1 1 count status cnt 2 cnt 1 cnt 0 0 d 5 :0 e latch count of selected counter(s) d 4 :0 e latch status of selected counter(s) d 3 :1 e select counter 2 d 2 :1 e select counter 1 d 1 :1 e select counter 0 d 0 : reserved for future expansion; must be 0 figure 10. read-back command format the read-back command may be used to latch multi- ple counter output latches (ol) by setting the count bit d5 e 0 and selecting the desired coun- ter(s). this single command is functionally equiva- lent to several counter latch commands, one for each counter latched. each counter's latched count is held until it is read (or the counter is repro- grammed). that counter is automatically unlatched when read, but other counters remain latched until they are read. if multiple count read-back commands are issued to the same counter without reading the 7
82C54 count, all but the first are ignored; i.e., the count which will be read is the count at the time the first read-back command was issued. the read-back command may also be used to latch status information of selected counter(s) by setting status bit d4 e 0. status must be latched to be read; status of a counter is accessed by a read from that counter. the counter status format is shown in figure 11. bits d5 through d0 contain the counter's programmed mode exactly as written in the last mode control word. output bit d7 contains the current state of the out pin. this allows the user to monitor the counter's output via software, possibly eliminating some hardware from a system. d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 output null rw1 rw0 m2 m1 m0 bcd count d 7 1 e out pin is 1 0 e out pin is 0 d 6 1 e null count 0 e count available for reading d 5 -d 0 counter programmed mode (see figure 7) figure 11. status byte null count bit d6 indicates when the last count written to the counter register (cr) has been loaded into the counting element (ce). the exact time this happens depends on the mode of the counter and is described in the mode definitions, but until the count is loaded into the counting element (ce), it can't be read from the counter. if the count is latched or read before this time, the count value will not reflect the new count just written. the operation of null count is shown in figure 12. this action: causes: a. write to the control null count e 1 word register: [ 1 ] b. write to the count null count e 1 register (cr); [ 2 ] c. new count is loaded null count e 0 into ce (cr x ce); [ 1 ] only the counter specified by the control word will have its null count set to 1. null count bits of other counters are unaffected. [ 2 ] if the counter is programmed for two-byte counts (least significant byte then most significant byte) null count goes to 1 when the second byte is written. figure 12. null count operation if multiple status latch operations of the counter(s) are performed without reading the status, all but the first are ignored; i.e., the status that will be read is the status of the counter at the time the first status read-back command was issued. both count and status of the selected counter(s) may be latched simultaneously by setting both count and status bits d5,d4 e 0. this is func- tionally the same as issuing two separate read-back commands at once, and the above discussions ap- ply here also. specifically, if multiple count and/or status read-back commands are issued to the same counter(s) without any intervening reads, all but the first are ignored. this is illustrated in figure 13. if both count and status of a counter are latched, the first read operation of that counter will return latched status, regardless of which was latched first. the next one or two reads (depending on whether the counter is programmed for one or two type counts) return latched count. subsequent reads return un- latched count. command description results d 7 d 6 d 5 d 4 d 3 d 2 d 1 d 0 11000010 read back count and status of count and status latched counter 0 for counter 0 11100100 read back status of counter 1 status latched for counter 1 11101100 read back status of counters 2, 1 status latched for counter 2, but not counter 1 11011000 read back count of counter 2 count latched for counter 2 11000100 read back count and status of count latched for counter 1, counter 1 but not status 11100010 read back status of counter 1 command ignored, status already latched for counter 1 figure 13. read-back command example 8
82C54 cs rd wr a 1 a 0 0 1 0 0 0 write into counter 0 0 1 0 0 1 write into counter 1 0 1 0 1 0 write into counter 2 0 1 0 1 1 write control word 0 0 1 0 0 read from counter 0 0 0 1 0 1 read from counter 1 0 0 1 1 0 read from counter 2 0 0 1 1 1 no-operation (3-state) 1 x x x x no-operation (3-state) 0 1 1 x x no-operation (3-state) figure 14. read/write operations summary mode definitions the following are defined for use in describing the operation of the 82C54. clk pulse: a rising edge, then a falling edge, in that order, of a counter's clk input. trigger: a rising edge of a counter's gate in- put. counter loading: the transfer of a count from the cr to the ce (refer to the ``functional descrip- tion'') mode 0: interrupt on terminal count mode 0 is typically used for event counting. after the control word is written, out is initially low, and will remain low until the counter reaches zero. out then goes high and remains high until a new count or a new mode 0 control word is written into the coun- ter. gate e 1 enables counting; gate e 0 disables counting. gate has no effect on out. after the control word and initial count are written to a counter, the initial count will be loaded on the next clk pulse. this clk pulse does not decrement the count, so for an initial count of n, out does not go high until n a 1 clk pulses after the initial count is written. if a new count is written to the counter, it will be loaded on the next clk pulse and counting will con- tinue from the new count. if a two-byte count is writ- ten, the following happens: 1) writing the first byte does not disable counting. out is set low immediately (no clock pulse re- quired). 2) writing the second byte allows the new count to be loaded on the next clk pulse. 3) when there is a count in progress, writing a new lsb before the counter has counted down to 0 and rolled over to ffffh, will stop the counter. however, if the lsb is loaded after the counter has rolled over to ffffh, so that an msb now exists in the counter, then the counter will not stop. this allows the counting sequence to be synchroniz- ed by software. again, out does not go high until n a 1 clk pulses after the new count of n is written. 9
82C54 if an initial count is written while gate e 0, it will still be loaded on the next clk pulse. when gate goes high, out will go high n clk pulses later; no clk pulse is needed to load the counter as this has already been done. 231244 8 note: the following conventions apply to all mode timing diagrams: 1. counters are programmed for binary (not bcd) counting and for reading/writing least significant byte (lsb) only. 2. the counter is always selected (cs always low). 3. cw stands for ``control word''; cw e 10 means a control word of 10, hex is written to the counter. 4. lsb stands for ``least significant byte'' of count. 5. numbers below diagrams are count values. the lower number is the least significant byte. the upper number is the most significant byte. since the counter is programmed to read/write lsb only, the most significant byte cannot be read. n stands for an undefined count. vertical lines show transitions between count values. figure 15. mode 0 mode 1: hardware retriggerable one-shot out will be initially high. out will go low on the clk pulse following a trigger to begin the one-shot pulse, and will remain low until the counter reaches zero. out will then go high and remain high until the clk pulse after the next trigger. after writing the control word and initial count, the counter is armed. a trigger results in loading the counter and setting out low on the next clk pulse, thus starting the one-shot pulse. an initial count of n will result in a one-shot pulse n clk cycles in dura- tion. the one-shot is retriggerable, hence out will remain low for n clk pulses after any trigger. the one-shot pulse can be repeated without rewriting the same count into the counter. gate has no effect on out. if a new count is written to the counter during a one- shot pulse, the current one-shot is not affected un- less the counter is retriggered. in that case, the counter is loaded with the new count and the one- shot pulse continues until the new count expires. 231244 9 figure 16. mode 1 10
82C54 mode 2: rate generator this mode functions like a divide-by-n counter. it is typicially used to generate a real time clock inter- rupt. out will initially be high. when the initial count has decremented to 1, out goes low for one clk pulse. out then goes high again, the counter re- loads the initial count and the process is repeated. mode 2 is periodic; the same sequence is repeated indefinitely. for an initial count of n, the sequence repeats every n clk cycles. gate e 1 enables counting; gate e 0 disables counting. if gate goes low during an output pulse, out is set high immediately. a trigger reloads the counter with the initial count on the next clk pulse; out goes low n clk pulses after the trigger. thus the gate input can be used to synchronize the counter. after writing a control word and initial count, the counter will be loaded on the next clk pulse. out goes low n clk pulses after the initial count is writ- ten. this allows the counter to be synchronized by software also. 231244 10 note: a gate transition should not occur one clock prior to terminal count. figure 17. mode 2 writing a new count while counting does not affect the current counting sequence. if a trigger is re- ceived after writing a new count but before the end of the current period, the counter will be loaded with the new count on the next clk pulse and counting will continue from the new count. otherwise, the new count will be loaded at the end of the current counting cycle. in mode 2, a count of 1 is illegal. mode 3: square wave mode mode 3 is typically used for baud rate generation. mode 3 is similar to mode 2 except for the duty cycle of out. out will initially be high. when half the ini- tial count has expired, out goes low for the remain- der of the count. mode 3 is periodic; the sequence above is repeated indefinitely. an initial count of n results in a square wave with a period of n clk cycles. gate e 1 enables counting; gate e 0 disables counting. if gate goes low while out is low, out is set high immediately; no clk pulse is required. a trigger reloads the counter with the initial count on the next clk pulse. thus the gate input can be used to synchronize the counter. after writing a control word and initial count, the counter will be loaded on the next clk pulse. this allows the counter to be synchronized by software also. writing a new count while counting does not affect the current counting sequence. if a trigger is re- ceived after writing a new count but before the end of the current half-cycle of the square wave, the counter will be loaded with the new count on the next clk pulse and counting will continue from the new count. otherwise, the new count will be loaded at the end of the current half-cycle. mode 3 is implemented as follows: even counts: out is initially high. the initial count is loaded on one clk pulse and then is decremented by two on succeeding clk pulses. when the count expires out changes value and the counter is re- loaded with the initial count. the above process is repeated indefinitely. odd counts: out is initially high. the initial count minus one (an even number) is loaded on one clk pulse and then is decremented by two on succeed- ing clk pulses. one clk pulse after the count ex- pires, out goes low and the counter is reloaded with the initial count minus one. succeeding clk pulses decrement the count by two. when the count expires, out goes high again and the counter is reloaded with the initial count minus one. the above process is repeated indefinitely. so for odd counts, 11
82C54 out will be high for (n a 1)/2 counts and low for (n b 1)/2 counts. 231244 11 note: a gate transition should not occur one clock prior to terminal count. figure 18. mode 3 mode 4: software triggered strobe out will be initially high. when the initial count ex- pires, out will go low for one clk pulse and then go high again. the counting sequence is ``triggered'' by writing the initial count. gate e 1 enables counting; gate e 0 disables counting. gate has no effect on out. after writing a control word and initial count, the counter will be loaded on the next clk pulse. this clk pulse does not decrement the count, so for an initial count of n, out does not strobe low until n a 1 clk pulses after the initial count is written. if a new count is written during counting, it will be loaded on the next clk pulse and counting will con- tinue from the new count. if a two-byte count is writ- ten, the following happens: 1) writing the first byte has no effect on counting. 2) writing the second byte allows the new count to be loaded on the next clk pulse. this allows the sequence to be ``retriggered'' by software. out strobes low n a 1 clk pulses after the new count of n is written. 231244 12 figure 19. mode 4 mode 5: hardware triggered strobe (retriggerable) out will initially be high. counting is triggered by a rising edge of gate. when the initial count has ex- pired, out will go low for one clk pulse and then go high again. 12
82C54 after writing the control word and initial count, the counter will not be loaded until the clk pulse after a trigger. this clk pulse does not decrement the count, so for an initial count of n, out does not strobe low until n a 1 clk pulses after a trigger. a trigger results in the counter being loaded with the initial count on the next clk pulse. the counting sequence is retriggerable. out will not strobe low for n a 1 clk pulses after any trigger. gate has no effect on out. if a new count is written during counting, the current counting sequence will not be affected. if a trigger occurs after the new count is written but before the current count expires, the counter will be loaded with the new count on the next clk pulse and counting will continue from there. 231244 13 figure 20. mode 5 signal low status or going rising high modes low 0 disables e enables counting counting 1 e 1) initiates e counting 2) resets output after next clock 2 1) disables counting initiates enables 2) sets output counting counting immediately high 3 1) disables counting initiates enables 2) sets output counting counting immediately high 4 disables e enables counting counting 5 e initiates e counting figure 21. gate pin operations summary mode min max count count 01 0 11 0 22 0 32 0 41 0 note: 0 is equivalent to 2 16 for binary counting and 10 4 for bcd counting figure 22. minimum and maximum initial counts 13
82C54 operation common to all modes programming when a control word is written to a counter, all control logic is immediately reset and out goes to a known initial state; no clk pulses are required for this. gate the gate input is always sampled on the rising edge of clk. in modes 0, 2, 3, and 4 the gate input is level sensitive, and the logic level is sampled on the rising edge of clk. in modes 1, 2, 3, and 5 the gate input is rising-edge sensitive. in these modes, a rising edge of gate (trigger) sets an edge-sensi- tive flip-flop in the counter. this flip-flop is then sam- pled on the next rising edge of clk; the flip-flop is reset immediately after it is sampled. in this way, a trigger will be detected no matter when it occursea high logic level does not have to be maintained until the next rising edge of clk. note that in modes 2 and 3, the gate input is both edge- and level-sensi- tive. in modes 2 and 3, if a clk source other than the system clock is used, gate should be pulsed immediately following wr of a new count value. counter new counts are loaded and counters are decre- mented on the falling edge of clk. the largest possible initial count is 0; this is equiva- lent to 2 16 for binary counting and 10 4 for bcd counting. the counter does not stop when it reaches zero. in modes 0, 1, 4, and 5 the counter ``wraps around'' to the highest count, either ffff hex for binary count- ing or 9999 for bcd counting, and continues count- ing. modes 2 and 3 are periodic; the counter reloads itself with the initial count and continues counting from there. 14
82C54 absolute maximum ratings * ambient temperature under bias.0 cto70 c storage temperature b 65 to a 150 c supply voltage b 0.5 to a 8.0v operating voltage a 4v to a 7v voltage on any inputgnd b 2v to a 6.5v voltage on any output gnd b 0.5v to v cc a 0.5v power dissipation 1 watt notice: this is a production data sheet. the specifi- cations are subject to change without notice. * warning: stressing the device beyond the ``absolute maximum ratings'' may cause permanent damage. these are stress ratings only. operation beyond the ``operating conditions'' is not recommended and ex- tended exposure beyond the ``operating conditions'' may affect device reliability. d.c. characteristics (t a e 0 cto70 c, v cc e 5v g 10%, gnd e 0v) (t a eb 40 cto a 85 c for extended temperature) symbol parameter min max units test conditions v il input low voltage b 0.5 0.8 v v ih input high voltage 2.0 v cc a 0.5 v v ol output low voltage 0.4 v i ol e 2.5 ma v oh output high voltage 3.0 v i oh eb 2.5 ma v cc b 0.4 v i oh eb 100 m a i il input load current g 2.0 m av in e v cc to 0v i ofl output float leakage current g 10 m av out e v cc to 0.0v i cc v cc supply current 20 ma clk freq e 8mhz 82C54 10mhz 82C54-2 i ccsb v cc supply current-standby 10 m a clk freq e dc cs e v cc . all inputs/data bus v cc all outputs floating i ccsb1 v cc supply current-standby 150 m a clk freq e dc cs e v cc . all other inputs, i/o pins e v gnd , outputs open c in input capacitance 10 pf f c e 1 mhz c i/o i/o capacitance 20 pf unmeasured pins c out output capacitance 20 pf returned to gnd (5) a.c. characteristics (t a e 0 cto70 c, v cc e 5v g 10%, gnd e 0v) (t a eb 40 cto a 85 c for extended temperature) bus parameters (note 1) read cycle symbol parameter 82C54-2 units min max t ar address stable before rd v 30 ns t sr cs stable before rd v 0ns t ra address hold time after rd u 0ns t rr rd pulse width 95 ns t rd data delay from rd v 85 ns t ad data delay from address 185 ns t df rd u to data floating 5 65 ns t rv command recovery time 165 ns note: 1. ac timings measured at v oh e 2.0v, v ol e 0.8v. 15
82C54 a.c. characteristics (continued) write cycle symbol parameter 82C54-2 units min max t aw address stable before wr v 0ns t sw cs stable before wr v 0ns t wa address hold time after wr u 0ns t ww wr pulse width 95 ns t dw data setup time before wr u 95 ns t wd data hold time after wr u 0ns t rv command recovery time 165 ns clock and gate symbol parameter 82C54-2 units min max t clk clock period 100 dc ns t pwh high pulse width 30 (3) ns t pwl low pulse width 50 (3) ns t r clock rise time 25 ns t f clock fall time 25 ns t gw gate width high 50 ns t gl gate width low 50 ns t gs gate setup time to clk u 40 ns t gh gate hold time after clk u 50 (2) ns t od output delay from clk v 100 ns t odg output delay from gate v 100 ns t wc clk delay for loading (4) 055ns t wg gate delay for sampling (4) b 540 ns t wo out delay from mode write 240 ns t cl clk set up for count latch b 40 40 ns notes: 2. in modes 1 and 5 triggers are sampled on each rising clock edge. a second trigger within 70 ns for the 82C54-2 of the rising clock edge may not be detected. 3. low-going glitches that violate t pwh ,t pwl may cause errors requiring counter reprogramming. 4. except for extended temp., see extended temp. a.c. characteristics below. 5. sampled not 100% tested. t a e 25 c. 6. if clk present at t wc min then count equals n a 2 clk pulses, t wc max equals count n a 1 clk pulse. t wc min to t wc max, count will be either n a 1orn a 2 clk pulses. 7. in modes 1 and 5, if gate is present when writing a new count value, at t wg min counter will not be triggered, at t wg max counter will be triggered. 8. if clk present when writing a counter latch or readback command, at t cl min clk will be reflected in count value latched, at t cl max clk will not be reflected in the count value latched. writing a counter latch or readback command between t cl min and t wl max will result in a latched count vallue which is g one least significant bit. extended temperature (t a eb 40 cto a 85 c for extended temperature) symbol parameter 82C54-2 units min max t wc clk delay for loading b 25 25 ns t wg gate delay for sampling b 25 25 ns 16
82C54 waveforms write 231244 14 read 231244 15 recovery 231244 16 17
82C54 clock and gate 231244 17 * last byte of count being written a.c. testing input, output waveform input/output 231244 18 a.c. testing: inputs are driven at 2.4v for a logic ``1'' and 0.45v for a logic ``0.'' timing measurements are made at 2.0v for a logic ``1'' and 0.8v for a logic ``0.'' a.c. testing load circuit 231244 19 c l e 150 pf c l includes jig capacitance revision summary the following list represents the key differences be- tween rev. 005 and 006 of the 82C54 data sheet. 1. references to and specifications for the 8 mhz 82C54 are removed. only the 10 mhz 82c52-2 remains in production. 18

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