F_Tof - Siemens SIMATIC S7 F Manual

Fail-Safe Blocks
8.10.4

F_TOF

Function
The block delays a falling edge by the time PT.
A rising edge at the input IN results in a rising edge at the output Q. A falling edge
at IN results in a falling edge at Q after PT has elapsed.
If the input IN changes to 1 before PT has elapsed, Q remains on 1.
The output ET indicates the time that has elapsed since the last falling edge at the
input IN, but only up to the value at the input PT. ET is reset if the input IN changes
to 1.
If PT < 0, the outputs Q and ET are reset.
Timing Diagram
IN
Q
ET
PT
Startup Characteristics
In the first cycle after a cold or warm restart or in the case of a first call, the timer is
reset.
I/Os
Name
Inputs: IN
PT
Outputs: Q
ET
Fail-Safe Systems
A5E00085588-03
PT PT
Data Type Explanation
F_BOOL Start input
F_TIME Length of the delay
F_BOOL Pulse output
F_TIME Elapsed time
Default
0
T#0 ms
0
T#0 ms
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