Beckhoff First Scan Bit Portable -

During the first cycle, the IF bFirstScan condition evaluates to true. The initialization code executes. bFirstScan is set to FALSE at the end of the block.

IF fbFirstScan.bFirstScan THEN // First cycle only bResetDrives := TRUE; bStartupComplete := FALSE; tStartupTimer(IN:=FALSE); END_IF beckhoff first scan bit

// 3. Request axes to home (if needed) fbAxis1.bHomeRequest := TRUE; During the first cycle, the IF bFirstScan condition

PROGRAM MAIN VAR bFirstScan : BOOL := TRUE; // Initialize as TRUE bInitialized : BOOL; END_VAR // --- Logic --- IF bFirstScan THEN // Place all your initialization code here iSpeed := 100; bInitializeDone := TRUE; bFirstScan := FALSE; // Turn off after first run END_IF; // ... Rest of your program Use code with caution. Method B: Using PLC Attributes (TwinCAT 3 Best Practice) IF fbFirstScan

This method is robust and directly ties the initialization code to the lifecycle of the PLC task itself.

A simpler, more manual approach uses a boolean variable to track if the first scan has already occurred. This method is particularly useful for quick prototyping or simple programs.

🔄 Forces your Sequential Function Chart (SFC) or CASE statements to jump to the 'IDLE' or 'INIT' state regardless of where they were during the last shutdown.