: The official Tc3_Standard provides a clean helper:
: The INIT section runs before the first cyclic scan. This is actually earlier than a typical "first scan bit." If you need to guarantee initialization occurs before any other logic, INIT is superior. beckhoff first scan bit
Caveat : This method is cycle-dependent. If your cycle time is 10ms, set PT to at least 1ms — but ensure it's longer than one cycle but shorter than two. With TwinCAT 3, Beckhoff introduced the Tc3_Standard library, which includes a dedicated function block: F_TRIG combined with a system flag is no longer needed. Instead, use: : The official Tc3_Standard provides a clean helper:
// Main cyclic code myOutput := TRUE; // Normal logic If your cycle time is 10ms, set PT
: If you call the program multiple times (e.g., as an action or method), the INIT behavior may change. Use it carefully within the main cyclic task. Part 4: Best Practice – The FB_Init Method (Object-Oriented) For advanced TwinCAT 3 users working with Function Blocks, the most elegant and robust "first scan" is not a bit at all—it's the object constructor: FB_Init .
For engineers working with Beckhoff TwinCAT 3 (and TwinCAT 2), the concept of the (often implemented via the bInit or bFirst variable) is the cornerstone of safe and robust machine initialization.