Beckhoff First Scan Bit [new] -

You can use the attribute 'call_after_init' pragma to mark a method to be executed immediately after the FB_init call but still before the first cyclic call of the FB. This gives you another layer of control over the object's lifecycle.

On the second scan, bInitialized is TRUE , meaning NOT bInitialized is FALSE . The initialization block is bypassed for as long as the PLC remains in Run Mode. Method 2: System Variables ( TwinCAT_SystemInfoVarList ) beckhoff first scan bit

Unlike some traditional PLCs (like Allen-Bradley or Siemens) that provide a dedicated, built-in system variable for this purpose out of the box, Beckhoff’s TwinCAT environment handles this differently. Because TwinCAT is based on the IEC 61131-3 standard, developers have a few explicit, flexible methods to detect and utilize the first execution cycle. Method 1: Using the Standard System Variable ( PLC_STARTUP ) You can use the attribute 'call_after_init' pragma to

The Beckhoff First Scan bit is your "clean slate" button. Whether you use a simple boolean flag or the system's cycle counter, implementing this ensures that your machine starts up with the correct parameters every time, preventing "ghost" data from causing erratic behavior during commissioning. The initialization block is bypassed for as long

Also, if you are working with multiple tasks and need to know which one is running, I can show you how to use GETCURTASKINDEX . Share public link

This is particularly useful for initializing complex data structures, allocating memory with __NEW , or passing parameters to function blocks before they are used in the program.