FP_DETECT_CHANGE

Detect changes in data

This FP instruction detects changes in a value at input s_Current by comparing it with its former value that is stored at input/output d1_Previous. If the new input value at s_Current is not equal to the former value, the function assigns the new value to the input/output d1_Previous. To signal the change, the system output d2 is set to TRUE.

Parameters

Input

s_Current (INT, DINT, UINT, UDINT, REAL, LREAL): Data area for detecting data changes

Input/output

d1_Previous (INT, DINT, UINT, UDINT, REAL, LREAL): Data area where the data from the previous execution is stored.

Output

d2 (BOOL): Set to TRUE if a change is detected

Error flags

sys_bIsOperationErrorHold (turns to TRUE and remains TRUE)

if the area specified using the index modifier exceeds the limit.

sys_bIsOperationErrorNonHold (turns to TRUE for one scan)

if the area specified using the index modifier exceeds the limit.

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
		bStart: BOOL:=FALSE;
			(*activates the function*)
		diCurrent_value: DINT:=101;
			(*value whose status 
should be monitored*)
		diPrevious_value: DINT:=0;
			(*dummy value for storing 
the former present value*)
	END_VAR

POU body

When the variable bStart is set to TRUE, the function is carried out.

LD body

BODY
    WORKSPACE
        NETWORK_LIST_TYPE := NWTYPELD ;
        ACTIVE_NETWORK := 0 ;
    END_WORKSPACE
    NET_WORK
        NETWORK_TYPE := NWTYPELD ;
        NETWORK_LABEL :=  ;
        NETWORK_TITLE :=  ;
        NETWORK_HEIGHT := 6 ;
        NETWORK_BODY
B(B_CONTACT,,bStart,6,2,8,4,);
B(B_VARIN,,diCurrent_value,10,3,12,5,);
B(B_VARIN,,diPrevious_value,10,4,12,6,);
B(B_F,FP_DETECT_CHANGE!,,12,1,24,6,,?DEN?Ds_Current?Dd1_Previous?Ad1_Previous?AENO?Cd2);
B(B_VAROUT,,bValueChanged,24,3,26,5,);
L(1,3,6,3);
L(8,3,12,3);
L(1,0,1,6);
        END_NETWORK_BODY
    END_NET_WORK
END_BODY

ST body

IF bStart then
    FP_DETECT_CHANGE(s_Current := diCurrent_value, d_Previous := diPrevious_value);
END_IF;