First Scan Bit - Beckhoff

VAR fbGetCurTaskIndex : GETCURTASKINDEX; END_VAR

The is a system-generated boolean flag that is TRUE for exactly one PLC cycle after:

Beckhoff provides additional system flags for finer control: beckhoff first scan bit

// Main cyclic code myOutput := TRUE; // Normal logic

FirstScan gives you a deterministic moment to reset, preset, or home everything before normal operation begins. VAR fbGetCurTaskIndex : GETCURTASKINDEX; END_VAR The is a

Call it at the beginning of your main cycle:

For smaller TwinCAT 2 projects or heavily standardized libraries, many developers use a Global Variable List (GVL) dedicated to system flags. You can configure a simple boolean flag to latch and toggle off. fbFirstScan(); bInitTriggered is now TRUE

fbFirstScan();

bInitTriggered is now TRUE . The code hits the ELSE condition. bFirstScan is set to FALSE and remains FALSE until the PLC restarts. Method 3: FB Init Methods (Object-Oriented Programming)

To make your machine's startup routine bulletproof, consider these best practices.