DFN

Falling edge differential

The DFN instruction executes and turns ON output o for a single scan duration if the trigger i changes from an ON to an OFF state.

Parameters

Input

Unnamed input (BOOL)

Output

Unnamed output (BOOL)

Remarks

Be careful when programming with commands that effect the order in which a program is carried out, e.g. jump or loop instructions within a sequential function chart or a function block. The order of the instructions might change depending on the time when the instruction is carried out or the input value. Specific basic JUMP and LOOP instructions are:

MC to MCE
JP to LBL
F19_SJP to LBL
LOOP to LBL

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
		Decrement: BOOL:=FALSE;
		Counter: INT:=0;
	END_VAR

POU body

Each falling edge at the input Decrement decrements the couter.

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_F,DFN!,Instance,7,0,12,3,,?Di?Co);
B(B_VARIN,,Decrement,5,1,7,3,);
B(B_F,E_SUB!,Instance,16,0,22,5,,?DEN?D?D?AENO?C);
B(B_VARIN,,Counter,14,2,16,4,);
B(B_VARIN,,1,14,3,16,5,);
B(B_VAROUT,,Counter,22,2,24,4,);
L(12,2,16,2);
L(1,0,1,5);
        END_NETWORK_BODY
    END_NET_WORK
END_BODY

ST body

IF DFN(Decrement) then
    Counter:=Counter-1;
END_IF;