Pulse Blocks - Siemens SIMATIC S7 F Manual

Fail-Safe Blocks
8.11

Pulse Blocks

Block
F_F_TRIG
F_R_TRIG
F_LIM_TI
8.11.1 F_F_TRIG
Function
The block checks the input variable for the occurrence of a falling edge and indicates at
the output whether an edge has been detected. At a falling edge of the input pulse CLK,
the output Q is set to 1 until the next call of the block.
Timing Diagram
CLK
Q
Startup Characteristics
In the first cycle after a cold or warm restart or in the case of a first call, no edge is
detected.
I/Os
Name
Input: CLK
Output: Q
Fail-Safe Systems
A5E00085588-03
Description
Detection of the falling edge
Detection of the rising edge
Asymmetrical limiter of TIME values
Data Type Explanation
F_BOOL Input pulse
F_BOOL Output pulse
Default
0
0
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