Siemens SIMATIC S7 F, Manual

Page: 297 / 354

Fail-Safe Blocks
Fail-Safe Systems
A5E00085588-03
8-109
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
Q
IN
PT
ET
PT 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 Data Type Explanation Default
Inputs: IN F_BOOL Start input 0
PT F_TIME Length of the delay T#0 ms
Outputs: Q F_BOOL Pulse output 0
ET F_TIME Elapsed time T#0 ms