Fail-Safe Blocks
Fail-Safe Systems
A5E00085588-03
8-111
8.11 Pulse Blocks
Block Description
F_F_TRIG Detection of the falling edge
F_R_TRIG Detection of the rising edge
F_LIM_TI Asymmetrical limiter of TIME values
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 Data Type Explanation Default
Input:
CLK F_BOOL Input pulse 0
Output:
Q F_BOOL Output pulse 0
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