118 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 3 Timer and Counter Instructions (TON, TOF, RTO, TONR, TOFR, RTOR, CTU, CTD, CTUD, RES)
Execution:
Condition Relay Ladder Action
Prescan The .EN, .TT, and .DN bits are cleared.
The .ACC value is cleared.
The rung-condition-out is set to false.
Rung-condition-in is false The .EN, .TT, and .DN bits are cleared.
The .ACC value is cleared.
The rung-condition-out is set to false.
Postscan The rung-condition-out is set to false.
Examine .DN
Bit
.DN Bit = 1
.DN Bit = 0
.EN bit is set.
TT bit is set
last_time = current_time
Rung-condition-in is true.
Examine .ACC
.ACC ≥ .PRE
.ACC < .PRE
.TT bit is set.
.ACC = .ACC + (current_time - last_time)
last_time = current_time
.ACC Value Rolls Over
No
Yes
Examine .EN Bit
.EN Bit = 0
.EN Bit = 1
Rung-condition-out is
set to true.
End
.DN is set
.TT bit is cleared
.ACC = 2,147,483,647
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