Simple flag:
To detect the first scan in Beckhoff TwinCAT, you can read the system task info or create a classic initialization variable. beckhoff first scan bit
Some hardware modules (e.g., high-speed counters, PWM generators) need a setup block executed exactly once. Simple flag: To detect the first scan in
// -- Reset the first scan trigger for next init -- bInit := FALSE; If you do it at the top, the
If you use a manual first scan bit, ensure it is set to FALSE at the very end of your program. If you do it at the top, the rest of your logic won't see the TRUE state.
In TwinCAT 2, it is typically FirstCycle or FirstScan . In TwinCAT 3, it is available via Tc2_System function block or directly as FirstScan in some contexts.
The system automatically resets this bit to FALSE after the first cycle completes.