Program instructions
7.17 Timer
S7-200 SMART
336 System Manual, 09/2015, A5E03822230-AC
Note
Avoid timer number conflicts
You cannot use the same timer number for both a TON and TOF timer. For example, you
cannot have both a TON T32 and a TOF T32.
Note
To guarantee a minimum time interval, increase the preset value (PV) by 1.
For example: To ensure a
minimum timed interval of at least 2100 ms for a 100-
ms timer, set
the PV to 22.
TON and TONR timer operation
The TON and TONR instructions begin timing when the enabling input IN is ON. When the
current value is equal to or greater than the preset time, the timer bit is set ON.
● The current value of a TON timer is cleared when the enabling input is OFF.
● The current value of the TONR timer is maintained when the enabling input is OFF. You
can use the TONR timer to accumulate time when the input IN is ON. Use the Reset
instruction (R) to clear the current value of the TONR.
● Both the TON and the TONR timers continue timing after the preset time is reached, and
they stop timing at the maximum value of 32,767.
The TOF instruction is used to delay turning an output OFF for a fixed period of time after the
input turns OFF. When the enabling input turns ON, the timer bit turns ON immediately, and
the current value is set to 0. When the input turns OFF, timing begins and continues until the
current time equals the preset time.
● When the preset is reached, the timer bit turns OFF and the current value stops
incrementing; however, if the enabling input turns ON again before the TOF reaches the
preset value, the timer bit remains ON.
● The enabling input must make an ON-OFF transition for a TOF timer to begin timing the
OFF-delay time interval.
● If a TOF timer is inside an SCR region and the SCR region is inactive, then the current
value is set to 0, the timer bit is turned OFF, and the current value does not increment.
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