F_TRIG

Detecting a falling edge

The function block F_TRIG (falling edge trigger) allows you to recognize a falling edge at an input.

Parameters

Input

CLK (BOOL)

signal input

detects falling edge for clock

Output

Q (BOOL)

signal output

is set for each falling edge at the signal input CLK (clock)

Remarks

The output Q of a function block F_TRIG remains set for a complete PLC cycle after the occurrence of a falling edge (status change TRUE -> FALSE) at the CLK input and is then reset in the following cycle.

Example

POU header

All input and output variables used for programming this function have been declared in the POU header. The same POU header is used for all programming languages.

	VAR
		copy_name: F_TRIG;
		signal_input: BOOL:=FALSE;
		signal_output: BOOL:=FALSE;
	END_VAR

POU body

Signal_output will be set, if a falling edge is detected at signal_input.

LD body

BODY
    WORKSPACE
        NETWORK_LIST_TYPE := NWTYPELD ;
        ACTIVE_NETWORK := 0 ;
    END_WORKSPACE
    NET_WORK
        NETWORK_TYPE := NWTYPELD ;
        NETWORK_LABEL :=  ;
        NETWORK_TITLE :=  ;
        NETWORK_HEIGHT := 5 ;
        NETWORK_BODY
B(B_FB,F_TRIG!,copy_name,9,1,15,4,,?BCLK?AQ);
B(B_CONTACT,,signal_input,4,2,6,4,);
B(B_COIL,,signal_output,19,2,21,4,);
L(1,3,4,3);
L(6,3,9,3);
L(15,3,19,3);
L(1,0,1,5);
        END_NETWORK_BODY
    END_NET_WORK
END_BODY

ST body

copy_name( CLK:= signal_input ,
        Q=> signal_output );

IL body

If you want to call the function block in an instruction list, enter the following: