Allen-Bradley Logix5000 Reference Manual page 127

Condition
Prescan
Rung-condition-in is false
Rung-condition-in is true
Examine .DN bit.
Examine .EN Bit.
.TT bit is set.
.ACC = .ACC + (current_time - last_time)
last_time = current_time
.ACC value rolls over.
.ACC = 2,147,483,647
Postscan
Timer and Counter Instructions (TON, TOF, RTO, TONR, TOFR, RTOR, CTU, CTD, CTUD, RES)
Execution:
Relay Ladder Action
The .EN, .TT, and .DN bits are cleared.
The .ACC value is not modified.
The rung-condition-out is set to false.
The .EN and .TT bits are cleared.
The .DN bit is not modified.
The .ACC value is not modified.
The rung-condition-out is set to false.
.DN Bit = 1
.DN Bit = 0
.EN Bit = 0
.EN Bit = 1
No
Yes
The rung-condition-out is set to false.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
.EN bit is set.
.TT bit is set.
last_time = current_time
Examine .ACC
Rung-condition-out is set to true.
End
Chapter 3
.ACC ≥ .PRE
.DN is set.
.ACC < .PRE
.TT bit is cleared.
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