Beckhoff First Scan Bit High Quality Jun 2026

Unlike some other PLC platforms (like Allen-Bradley or Siemens) that have a pre-defined system bit (e.g., First_Scan ), Beckhoff TwinCAT requires you to create this bit yourself. Fortunately, it is very simple to do. Method A: The Classic TwinCAT Approach (Code-Based)

IF NOT bInitialized THEN // Initialization code here bInitialized := TRUE; END_IF Use code with caution. Copied to clipboard

Do you need to initialize variables that must be ?

The First Scan Bit is the "ignition switch" of a TwinCAT program. By isolating startup logic into this single-cycle window, engineers ensure that the system begins its operation from a known, predictable state beckhoff first scan bit

fbFirstScan();

VAR RETAIN powerCycleCounter : UDINT; END_VAR

If you encounter difficulties with your specific Beckhoff hardware platform or TwinCAT version, consult the Beckhoff Information System (Infosys) or reach out to your local Beckhoff support representative for platform-specific guidance. Unlike some other PLC platforms (like Allen-Bradley or

In , this is achieved using the First Scan Bit (also known as the First Cycle Bit).

// -- Reset the first scan trigger for next init -- bInit := FALSE;

VAR bInitialScan : BOOL := TRUE; // Initialized to TRUE on startup END_VAR IF bInitialScan THEN // Startup logic bInitialScan := FALSE; // Permanent reset after first run END_IF Use code with caution. Copied to clipboard 3. Applications and Best Practices The first scan bit is essential for: Copied to clipboard Do you need to initialize

In Beckhoff TwinCAT, the equivalent of a "first scan bit" is the variable found within the system task information. This bit is automatically set to TRUE only during the very first execution cycle of a PLC task, making it ideal for one-time initialization logic. How to Access the First Scan Bit

: Triggering handshake or connection logic that only needs to happen once upon startup. Safety Resets