Beckhoff First Scan Bit -

. If multiple Function Blocks rely on the first scan bit to initialize, the order of execution matters. Developers must ensure that hardware I/O is actually "Ready" before the first scan logic attempts to write to it.

Without a first scan flag, you cannot reliably distinguish between:

By utilizing the standard initialization behavior of variables in TwinCAT, you can create a self-resetting flag. beckhoff first scan bit

This ensures a clean, new log file is created each time the controller starts, without overwriting historical data.

PROGRAM MAIN VAR fbGetCurTaskIndex : GETCURTASKINDEX; // Function block to find active task index bFirstScan : BOOL; // Our dedicated local first scan variable END_VAR // 1. Invoke the system function block to determine the current task index fbGetCurTaskIndex(); // 2. Extract the FirstCycle boolean flag from the global system task array bFirstScan := _TaskInfo[fbGetCurTaskIndex.index].FirstCycle; // 3. Execute your targeted one-time initialization routine IF bFirstScan THEN // Place one-time initialization code here FormatStorageDrives(); LoadDefaultCalibrationValues(); SetStateMachineToDefault(); END_IF Use code with caution. Why Choose Method 1? Without a first scan flag, you cannot reliably

PROGRAM MAIN VAR bFirstScan : BOOL; END_VAR // Check the boot count or execution cycle of the current task // Task ID 1 is typically the standard PLC task bFirstScan := (_TaskInfo[1].CycleCount = 0); IF bFirstScan THEN // Execute initialization routines here END_IF; Use code with caution.

(without download) → Counter does not increment (warm start without new program) → In many cases, bFirstScan stays FALSE here unless configured to detect warm starts. Invoke the system function block to determine the

bFirstScan := FALSE; (* Set to false so this never runs again *)