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ON

Statement - Conditional execution of statements.

The ON instruction provides a simpler syntax for checking the rising edgeA rising edge is the transition of a digital signal from low to high. It is also called positive edge of a Boolean condition.

Syntax

ON <BOOL expression> DO
   <statements>
END_DO;

Remarks

Statements within the ON structure are executed only when the Boolean expression rises from FALSE to TRUE. The ON instruction avoids systematic use of the R_TRIG function block or other "last state" flags.

The ON syntax is available in any program, sub-program or UDFB"User Defined Function Block" UDFB can be used as a sub-function block in another program of the application. It is described using FBD, LD, ST or IL language. Input / output parameters of a UDFB (as well as private variables) are declared in the variable editor as local variables of the UDFB.

This statement is an extension to the standard and is not IEC61131-3IEC 61131-3 is the third part of the open international standard IEC 61131. The current (second) edition was published in 2003. IEC 61131-3 currently defines five programming languages for programmable control systems It deals with programming languages and defines two graphical and two textual PLC programming language standards compliant.

This instruction should not be used inside UDFBs. This instruction is not UDFB safe.

ST Language

(* This example counts the rising edges of variable bIN *)
ON bIN DO
   diCount := diCount + 1;
END_DO;

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