82C54

82C54 CHMOS PROGRAMMABLE INTERVAL TIMER Y Compatible with all Intel and most other microprocessors High Speed ‘‘Zero Wait State’’ Operation with 8 MHz 8086 88 and 80186 188 Handles Inputs from DC 10 MHz for 82C54-2 Available in EXPRESS Standard Temperature Range Extended Temperature Range Y Y Three independent 16-bit counters Low Power CHMOS ICC e 10 mA 8 MHz Count frequency Completely TTL Compatible Six Programmable Counter Modes Binary or BCD counting Status Read Back Command Available in 24-Pin DIP and 28-Pin PLCC Y Y Y Y Y Y Y Y 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 – 3 PLASTIC LEADED CHIP CARRIER 231244 – 1 Figure 1 82C54 Block Diagram 231244 – 2 Diagrams are for pin reference only Package sizes are not to scale Figure 2 82C54 Pinout October 1994 Order Number 231244-006 82C54 Table 1 Pin Description Symbol DIP D7-D0 CLK 0 OUT 0 GATE 0 GND OUT 1 GATE 1 CLK 1 GATE 2 OUT 2 CLK 2 A1 A 0 1-8 9 10 11 12 13 14 15 16 17 18 20-19 Pin Number PLCC 2-9 10 12 13 14 16 17 18 19 20 21 23-22 IO I O I O I I I O I I Data Bidirectional tri-state data bus lines connected to system data bus Clock 0 Clock input of Counter 0 Output 0 Output of Counter 0 Gate 0 Gate input of Counter 0 Ground Power supply connection Out 1 Output of Counter 1 Gate 1 Gate input of Counter 1 Clock 1 Clock input of Counter 1 Gate 2 Gate input of Counter 2 Out 2 Output of Counter 2 Clock 2 Clock input of Counter 2 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 A1 0 0 1 1 CS 21 24 I A0 0 1 0 1 Selects Counter 0 Counter 1 Counter 2 Control Word Register Type Function RD WR VCC NC 22 23 24 26 27 28 1 11 15 25 I I Chip Select A low on this input enables the 82C54 to respond to RD and WR signals RD and WR are ignored otherwise Read Control This input is low during CPU read operations Write Control This input is low during CPU write operations Power a 5V power supply connection No Connect 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 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 problems in any microcomputer system the generation of accurate time delays under software control Instead of setting up timing loops in software the programmer configures the 82C54 to match his requirements and programs one of the counters for the de2         Real time clock Even counter Digital one-shot Programmable rate generator Square wave generator Binary rate multiplier Complex waveform generator Complex motor controller 82C54 Block Diagram DATA BUS BUFFER This 3-state bi-directional 8-bit buffer is used to interface the 82C54 to the system bus (see Figure 3) CONTROL WORD REGISTER The Control Word Register (see Figure 4) is selected by the Read Write Logic when A1 A0 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 – 4 Figure 3 Block Diagram Showing Data Bus Buffer and Read Write Logic Functions 231244 – 5 READ WRITE LOGIC The Read Write Logic accepts inputs from the system bus and generates control signals for the other functional blocks of the 82C54 A1 and A0 select one of the three counters or the Control Word Register 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 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 system clock source Another technique is to externally synchronize the WR and CLK input signals This is done by gating WR with CLK Figure 4 Block Diagram Showing Control Word Register and Counter Functions COUNTER 0 COUNTER 1 COUNTER 2 These three functional blocks are identical in operation 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 determine how the Counter operates 3 82C54 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 transferred to the CE simultaneously CRM and CRL 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 outside world through the Control Logic 82C54 SYSTEM INTERFACE 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 ReadBack command ) The actual counter is labelled CE (for ‘‘Counting Element’’) It is a 16-bit presettable synchronous down counter OLM and OLL 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 ‘‘follow’’ the CE but if a suitable Counter Latch Command 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 CRM and CRL (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 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 programming Basically the select inputs A0 A1 connect to the A0 A1 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 systems 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 A1 A0 e 11 The Control Word itself specifies which Counter is being programmed By contrast initial counts are written into the Counters not the Control Word Register The A1 A0 inputs 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 A1 A0 e 11 CS e 0 RD e 1 D7 SC1 SC Select Counter SC1 SC0 0 0 1 1 0 1 0 1 Select Counter 0 Select Counter 1 Select Counter 2 Read-Back Command (See Read Operations) WR e 0 D6 SC0 D5 RW1 D4 RW0 D3 M2 M D2 M1 D1 M0 D0 BCD MODE M2 0 0 X X 1 1 M1 0 0 1 1 0 0 M0 0 1 0 1 0 1 Mode 0 Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 RW Read Write RW1 RW0 0 0 1 1 0 1 0 1 Counter Latch Command (see Read Operations) Read Write least significant byte only Read Write most significant byte only Read Write least significant byte first then most significant byte BCD 0 1 Binary Counter 16-bits Binary Coded Decimal (BCD) Counter (4 Decades) NOTE Don’t care bits (X) should be 0 to insure compatibility with future Intel products Figure 7 Control Word Format 5 82C54 struction sequence is required Any programming sequence that follows the conventions above is acceptable A new initial count may be written to a Counter at any time without affecting the Counter’s programmed 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 A1 1 1 1 1 1 0 0 0 0 A1 1 1 0 1 0 0 1 0 1 A0 1 1 1 0 0 1 1 0 0 A0 1 1 1 1 0 1 0 0 0 Write Operations The programming procedure for the 82C54 is very flexible Only two conventions need to be remembered 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 significant byte and then most significant byte) Since the Control Word Register and the three Counters have separate addresses (selected by the A1 A0 inputs) and each Control Word specifies the Counter it applies to (SC0 SC1 bits) no special inA1 1 0 0 1 0 0 1 1 1 A1 1 1 1 1 0 0 0 0 1 A0 1 0 0 1 1 1 1 0 0 A0 1 1 1 0 1 0 0 1 0 Control Word LSB of count MSB of count Control Word LSB of count MSB of count Control Word LSB of count MSB of count Counter 0 Counter 0 Counter 0 Counter 1 Counter 1 Counter 1 Counter 2 Counter 2 Counter 2 Control Word Control Word Control Word LSB of count MSB of count LSB of count MSB of count LSB of count MSB of count Counter 2 Counter 1 Counter 0 Counter 2 Counter 2 Counter 1 Counter 1 Counter 0 Counter 0 Control Word Counter Word Control Word LSB of count LSB of count LSB of count MSB of count MSB of count MSB of count Counter 0 Counter 1 Counter 2 Counter 2 Counter 1 Counter 0 Counter 0 Counter 1 Counter 2 Control Word Control Word LSB of count Control Word LSB of count MSB of count LSB of count MSB of count MSB of count Counter 1 Counter 0 Counter 1 Counter 2 Counter 0 Counter 1 Counter 2 Counter 0 Counter 2 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 easily 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 perform 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 Otherwise the count may be in the process of changing when it is read giving an undefined result 6 82C54 gramming operations of other Counters may be inserted 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 2 3 4 Read least significant byte Write new least significant byte Read most significant byte Write new most significant byte COUNTER LATCH COMMAND The second method uses the ‘‘Counter Latch Command’’ Like a Control Word this command is written to the Control Word Register which is selected when A1 A0 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 A1 A0 e 11 CS e 0 RD e 1 WR e 0 D7 SC1 D6 SC0 D5 0 D4 0 D3 X D2 X D1 X D0 X SC1 SC0 - specify counter to be latched SC1 0 0 1 1 SC0 0 1 0 1 Counter 0 1 2 Read-Back Command 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 counter(s) The command is written into the Control Word Register and has the format shown in Figure 10 The command applies to the counters selected by setting their corresponding bits D3 D2 D1 e 1 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 A0 A1 e 11 CS e 0 RD e 1 WR e 0 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 Counter’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 according 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- D5 D4 D3 D2 D1 D0 D 7 D6 1 1 COUNT STATUS CNT 2 CNT 1 CNT 0 0 D5 D4 D3 D2 D1 D0 0 e Latch count of selected counter(s) 0 e Latch status of selected counter(s) 1 e Select counter 2 1 e Select counter 1 1 e Select counter 0 Reserved for future expansion must be 0 Figure 10 Read-Back Command Format The read-back command may be used to latch multiple counter output latches (OL) by setting the COUNT bit D5 e 0 and selecting the desired counter(s) This single command is functionally equivalent 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 reprogrammed) 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 THIS ACTION A Write to the control word register 1 B Write to the count register (CR) 2 C New count is loaded into CE (CR x CE) CAUSES Null count e 1 Null count e 1 Null count e 0 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 functionally the same as issuing two separate read-back commands at once and the above discussions apply 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 unlatched count D7 D6 D5 D4 D3 D2 D1 D0 NULL OUTPUT RW1 RW0 M2 M1 M0 BCD COUNT D7 1 e 0e D6 1 e 0e D5-D0 Out Pin is 1 Out Pin is 0 Null count Count available for reading 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 Command D7 D6 D5 D4 D3 D2 D1 D0 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 0 1 1 0 1 0 1 0 0 0 0 1 0 0 0 0 0 0 Description Read back count and status of Counter 0 Read back status of Counter 1 Results Count and status latched for Counter 0 Status latched for Counter 1 Read back status of Counters 2 1 Status latched for Counter 2 but not Counter 1 Read back count of Counter 2 Read back count and status of Counter 1 Read back status of Counter 1 Count latched for Counter 2 Count latched for Counter 1 but not status Command ignored status already latched for Counter 1 Figure 13 Read-Back Command Example 8 82C54 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 continue from the new count If a two-byte count is written the following happens 1) Writing the first byte does not disable counting OUT is set low immediately (no clock pulse required) 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 synchronized by software Again OUT does not go high until N a 1 CLK pulses after the new count of N is written CS 0 0 0 0 0 0 0 0 1 0 RD 1 1 1 1 0 0 0 0 X 1 WR 0 0 0 0 1 1 1 1 X 1 A1 0 0 1 1 0 0 1 1 X X A0 0 1 0 1 0 1 0 1 X X Write into Counter 0 Write into Counter 1 Write into Counter 2 Write Control Word Read from Counter 0 Read from Counter 1 Read from Counter 2 No-Operation (3-State) No-Operation (3-State) 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 input COUNTER LOADING the transfer of a count from the CR to the CE (refer to the ‘‘Functional Description’’) 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 Counter 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 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 duration 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 oneshot pulse the current one-shot is not affected unless the Counter is retriggered In that case the Counter is loaded with the new count and the oneshot pulse continues until the new count expires 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 231244 – 9 Figure 16 Mode 1 10 82C54 Writing a new count while counting does not affect the current counting sequence If a trigger is received 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 initial count has expired OUT goes low for the remainder 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 received 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 reloaded 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 succeeding CLK pulses One CLK pulse after the count expires 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 MODE 2 RATE GENERATOR This Mode functions like a divide-by-N counter It is typicially used to generate a Real Time Clock interrupt 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 reloads 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 written 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 82C54 OUT will be high for (N a 1) 2 counts and low for (N b 1) 2 counts 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 – 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 expires 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 continue from the new count If a two-byte count is written the following happens 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 expired 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 Signal Status Modes 0 1 Low Or Going Low Disables counting Rising High Enables counting 1) Initiates counting 2) Resets output after next clock 1) Disables counting 2) Sets output immediately high 1) Disables counting 2) Sets output immediately high Disables counting Initiates counting Initiates counting Enables counting 2 3 Initiates counting Enables counting 4 5 Enables counting Figure 21 Gate Pin Operations Summary MODE 0 1 2 3 4 MIN MAX COUNT COUNT 1 1 2 2 1 0 0 0 0 0 NOTE 0 is equivalent to 216 for binary counting and 104 for BCD counting Figure 22 Minimum and Maximum initial Counts 231244 – 13 Figure 20 Mode 5 13 82C54 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-sensitive 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 decremented on the falling edge of CLK The largest possible initial count is 0 this is equivalent to 216 for binary counting and 104 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 counting or 9999 for BCD counting and continues counting Modes 2 and 3 are periodic the Counter reloads itself with the initial count and continues counting from there 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-sensitive flip-flop in the Counter This flip-flop is then sampled 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 occurs a 14 82C54 ABSOLUTE MAXIMUM RATINGS Ambient Temperature Under Bias 0 C to 70 C b 65 to a 150 C Storage Temperature b 0 5 to a 8 0V Supply Voltage a 4V to a 7V Operating Voltage Voltage on any Input GND b 2V to a 6 5V Voltage on any Output GND b 0 5V to VCC a 0 5V Power Dissipation 1 Watt NOTICE This is a production data sheet The specifications 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 extended exposure beyond the ‘‘Operating Conditions’’ may affect device reliability D C CHARACTERISTICS (TA e 0 C to 70 C VCC e 5V g 10% GND e 0V) (TA e b 40 C to a 85 C for Extended Temperature) Symbol VIL VIH VOL VOH IIL IOFL ICC ICCSB Parameter Input Low Voltage Input High Voltage Output Low Voltage Output High Voltage Input Load Current Output Float Leakage Current VCC Supply Current VCC Supply Current-Standby 30 VCC b 0 4 g2 0 g 10 Min b0 5 Max 08 VCC a 0 5 04 Units V V V V V mA mA mA mA Test Conditions 20 IOL e 2 5 mA IOH e b 2 5 mA IOH e b 100 mA VIN e VCC to 0V VOUT e VCC to 0 0V Clk Freq e 8MHz 82C54 10MHz 82C54-2 20 10 CLK Freq e DC CS e VCC All Inputs Data Bus VCC All Outputs Floating CLK Freq e DC CS e VCC All Other Inputs I O Pins e VGND Outputs Open fc e 1 MHz Unmeasured pins returned to GND(5) ICCSB1 VCC Supply Current-Standby 150 mA CIN CI O COUT Input Capacitance I O Capacitance Output Capacitance 10 20 20 pF pF pF A C CHARACTERISTICS (TA e 0 C to 70 C VCC e 5V g 10% GND e 0V) (TA e b 40 C to a 85 C for Extended Temperature) BUS PARAMETERS (Note 1) READ CYCLE Symbol tAR tSR tRA tRR tRD tAD tDF tRV Parameter Min Address Stable Before RDv CS Stable Before RDv Address Hold Time After RDu RD Pulse Width Data Delay from RDv Data Delay from Address RDu to Data Floating Command Recovery Time 5 165 30 0 0 95 85 185 65 82C54-2 Max ns ns ns ns ns ns ns ns Units NOTE 1 AC timings measured at VOH e 2 0V VOL e 0 8V 15 82C54 A C CHARACTERISTICS (Continued) WRITE CYCLE Symbol tAW tSW tWA tWW tDW tWD tRV CLOCK AND GATE Symbol tCLK tPWH tPWL TR tF tGW tGL tGS tGH TOD tODG tWC tWG tWO tCL Parameter Min Clock Period High Pulse Width Low Pulse Width Clock Rise Time Clock Fall Time Gate Width High Gate Width Low Gate Setup Time to CLK Gate Hold Time After CLK 50 50 40 50(2) 100 100 0 b5 b 40 Parameter Min Address Stable Before WR CS Stable Before WR WR Pulse Width Data Setup Time Before WR Data Hold Time After WR Command Recovery Time 82C54-2 Max Units ns ns ns ns ns ns ns v u 0 0 0 95 95 0 165 v u Address Hold Time After WR u 82C54-2 Max DC 100 30(3) 50(3) 25 25 Units ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns u u Output Delay from CLKv Output Delay from Gatev CLK Delay for Loading(4) Gate Delay for Sampling(4) OUT Delay from Mode Write CLK Set Up for Count Latch 55 40 240 40 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 tPWH tPWL may cause errors requiring counter reprogramming 4 Except for Extended Temp See Extended Temp A C Characteristics below 5 Sampled not 100% tested TA e 25 C 6 If CLK present at TWC min then Count equals N a 2 CLK pulses TWC max equals Count N a 1 CLK pulse TWC min to TWC max count will be either N a 1 or N a 2 CLK pulses 7 In Modes 1 and 5 if GATE is present when writing a new Count value at TWG min Counter will not be triggered at TWG max Counter will be triggered 8 If CLK present when writing a Counter Latch or ReadBack Command at TCL min CLK will be reflected in count value latched at TCL max CLK will not be reflected in the count value latched Writing a Counter Latch or ReadBack Command between TCL min and TWL max will result in a latched count vallue which is g one least significant bit EXTENDED TEMPERATURE (TA e b 40 C to a 85 C for Extended Temperature) 82C54-2 Symbol Parameter Min Max b 25 tWC CLK Delay for Loading 25 tWG 16 Gate Delay for Sampling b 25 Units ns ns 25 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 A C TESTING LOAD CIRCUIT 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 ’’ 231244 – 19 CL e 150 pF CL includes jig capacitance REVISION SUMMARY The following list represents the key differences between 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