Beckhoff First Scan Bit [2024]

TwinCAT provides internal system information via the Tc2_System library. You can check if the current cycle is the very first one by looking at the system task info.

In Beckhoff’s TwinCAT 3 environment, there isn’t a single hard-coded bit in the global memory by default, but the system provides a specialized mechanism to create one that is far more powerful than a simple boolean. What is the First Scan Bit? beckhoff first scan bit

If you use the manual variable method, ensure the line bFirstScan := FALSE; is at the very bottom of your MAIN task. If you put it in a sub-function, other parts of your program might miss the "True" state. ensure the line bFirstScan := FALSE