120 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)
Timer Off Delay (TOF)
The TOF instruction is a non-retentive timer that accumulates time when the
instruction is enabled (rung-condition-in is false). This instruction is available in
structured text and function block as TOFR.
Operands:
Relay Ladder
TIMER Structure
Description: The TOF instruction accumulates time until the following occurs:
· The TOF instruction is disabled
· The .ACC ≥ .PRE
The time base is always 1 ms. For example, for a two-second timer, enter 2000 for
the .PRE value.
Operand Type Format Description
Timer TIMER Tag Timer structure
Preset DINT Immediate How long to delay (accumulate time)
Accum DINT Immediate Total milliseconds the timer has counted
Initial value is typically 0
Mnemonic Data Type Description
.EN BOOL The enable bit indicates that the TOF instruction is enabled.
.TT BOOL The timing bit indicates that a timing operation is in process
.DN BOOL The done bit is cleared when .ACC ≥ .PRE.
.PRE DINT The preset value specifies the value (1 ms units) that the accumulated value must reach before the
instruction clears the .DN bit.
.ACC DINT The accumulated value specifies the number of milliseconds that have elapsed since the TOF
instruction was enabled.
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