PMAC Quick Reference Guide Timers Timing commands like DWELL or DELAY are reserved only to motion programs and cannot be used for timing purposes on PLCs. Instead, PMAC has four 24-bit timers to write to and count down once per servo cycle. These timers are at registers X:$0700, Y:$0700, X:$0701, and Y:$0701. Usually a signed M-Variable is assigned to the timer; a value is written to it representing the desired time in servo cycles (multiply milliseconds by 8,388,608/I10); then the PLC waits until the M-Variable is less than 0. Example:
M90->X:$0700,0,24,S ; Timer register 1 (8388608/I10 msec) M91->Y:$0700,0,24,S ; Timer register 2 (8388608/I10 msec) M92->X:$0701,0,24,S ; Timer register 3 (8388608/I10 msec) M93->Y:$0701,0,24,S ; Timer register 4 (8388608/I10 msec) OPEN PLC3 CLEAR M1=0 ; Reset Output1 before start M90=1000*8388608/I10 ; Set timer to 1000 msec, 1 second WHILE (M90>0) ; Loop until counts to zero ENDWHILE M1=1 ; Set Output 1 after time elapsed DIS PLC3 ; disables PLC3 execution (needed in this example) CLOSE If more timers are needed, the best technique to use is in memory address X:0. This 24-bit register counts up once per servo cycle.
Store a starting value for this, then with each scan subtract the starting value from the current value and compare the difference to the amount of time to wait. Example: M0->X:$0,24 ; Servo counter register M85->X:$07F0,24 ; Free 24-bit register M86->X:$07F1,24 ; Free 24-bit register OPEN PLC 3 CLEAR M1=0 ; Reset Output1 before start M85=M0 ; Initialize timer M86=0 WHILE(M86 ; Time elapsed less than specified time?
M86=M0-M85 M86=M86*I10/8388608 ; Time elapsed so far in milliseconds ENDWHILE M1=1 ; Set Output 1 after time elapsed DISABLEPLC3 ; disables PLC3 execution (needed in this example) CLOSE Even if the servo cycle counter rolls over (starts from zero again after the counter is saturated), by subtracting into another 24-bit register rollover is handled gracefully. Rollover Example: M0 = 1000 M85 = 16777000 M86 = 1216 Carry-out bit PLC Programs 65 Bit 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 M0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 0 0 M85 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 0 1 0 0 0 M86 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 1 0 0 0 0 0 0