Lenze PLC Designer PLC Designer (R2-x) - Manual (Page 652)

L-force | PLC Designer
PLC Designer Libraries
650 DMS 3.2 EN 02/2011 TD29

Example in FBD:
Example in ST:
RTRIGInst(CLK:= VarBOOL1);
VarBOOL2 := RTRIGInst.Q;
F_TRIG
Provided by standard.lib.
The function block F_TRIG a falling edge.
FUNCTION_BLOCK F_TRIG
VAR_INPUT
CLK: BOOL;
END_VAR
VAR_OUTPUT
Q: BOOL;
END_VAR
VAR
M: BOOL := FALSE;
END_VAR
Q := NOT CLK AND NOT M;
M := NOT CLK;
The output Q and the help variable M will remain FALSE as long as the input variable
CLK returns TRUE. As soon as CLK returns FALSE, Q will first return TRUE, then M will be
set to TRUE. This means each time the function is called up, Q will return FALSE until
CLK has a rising followed by a falling edge.