In TwinCAT 3 (which supports Object-Oriented Programming), you can use the FB_init method
In TwinCAT 2 (CX1020, etc.), Standard.bInit was reliable. In TwinCAT 3, the system behavior changed slightly regarding Online Change (while logged in). If you perform a "Software Reset (Cold)" vs. "Original," the flag may behave differently. beckhoff first scan bit
To use this, you must first identify the index of the task currently running your code using the GETCURTASKINDEX function block: "Original," the flag may behave differently
The Beckhoff First Scan Bit is a valuable feature in the TwinCAT 3 programming environment, providing a way to execute specific actions or initialization code during the startup sequence. By understanding how to use the First Scan Bit effectively, programmers can create more efficient and reliable automation and control systems. Whether you're working on a simple startup task or a complex safety-related application, the First Scan Bit is an essential tool to have in your toolkit. Whether you're working on a simple startup task
IF _FIRSTSCAN THEN bEmergencyStop := FALSE; (* clear any leftover estop flag *) bMotorEnable := FALSE; (* motors off until operator starts *) END_IF
TwinCAT’s approach is very similar to CODESYS, given their shared roots.
In online mode, the first scan runs immediately after login. To debug, insert a JMP or use breakpoints carefully, or simulate the condition by forcing _FIRSTSCAN via a watch window (possible only if variable is writable — usually not).