Siemens SIMATIC S7-200, Системное руководство

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Program instructions
7.17 Timer
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
379
TOF timer operation
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.
Type Current >= Preset State of IN, the enabling input Power cycle / first scan
TON Timer bit ON
Current value continues
timing to 32,767
ON: Current value = timing value
OFF: Timer bit OFF, current value
= 0
Timer bit = OFF
Current value = 0
TONR
1
Timer bit ON
Current value continues
timing to 32,767
ON: Current value = timing value
OFF: Timer bit and current value
maintain last state and value
Timer bit = OFF
Current value can be
maintained
1
TOF Timer bit OFF
Current = Preset, stops
timing
ON: Timer bit ON, current value =
0
OFF: Timer begins timing after
ON-to-OFF transition
Timer bit = OFF
Current value = 0
1
The retentive timer current value can be assigned for retention through a power cycle. See Config-
uring the retentive ranges for details (Page 141).
Note
Using the Reset instruction with timer instructions
The TONR timer can only be reset with the Reset (R) instruction.
The TON and TOF timers can be reset by the timer's enable input and also the Reset (R)
instruction.
The Reset instruction performs the following actions:
• Timer bit = OFF
•
Timer current value = 0
• After a reset, TOF timers require the enable input to make the transition from ON-to-OFF
in order restart the OFF-delay timer.