REDGE

Typing REDGE evaluates the rising edge of a complete Boolean expression.
TIP: The IEC 61131-3 standard does not include the REDGE operator.
REDGE Operator
Name
REDGE
Syntax
<edge> := REDGE ( <boo_expression>,<memo_variable> );
Operands
First operand is any Boolean variable or complex expression
Second operand is an internal Boolean variable used to store the last state of the expression
Return value
TRUE when the expression changes from FALSE to TRUE
FALSE for all other cases
An execution cycle detects one rising edge of an expression with the REDGE operator. Call the REDGE operator from a function block instead of the R_TRIG function block.
TIP: Trigger edges for an expression with a variable other than the memory Boolean variable that stores the last state of the expression.
When the expression is a Boolean variable, declare a unique internal variable with same name and the EDGE_ prefix for use in the REDGE expressions for the variable. This internal variable prevents other REDGE operations from overwriting the memory variable.
Example
(* ST program using REDGE operator *)

(* this program counts the rising edges of a Boolean input *)

(* Bi120 is an input Boolean variable *)

(* Edge_Bi120 is the memory of the Bi120 variable state *)

If REDGE (Bi120, Edge_Bi120) Then

  Counter := Counter + 1;

End_if;
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