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.
If you need a first scan bit that works across multiple programs and tasks, use the Tc2_System or Tc3_System library. beckhoff first scan bit
Most TwinCAT developers create a global boolean variable and set it to TRUE by default. At the very end of their main program, they set it to FALSE . VAR_GLOBAL bFirstScan : BOOL := TRUE; END_VAR Use code with caution. Main Logic (MAIN PRG): In TwinCAT 2, it is typically FirstCycle or FirstScan
Which of these two methods are you planning to use for your specific project? Beckhoff CX1010 first scan | PLCtalk - Interactive Q & A Most TwinCAT developers create a global boolean variable
⚠️ Always use the first scan bit to put your machine into a Safe State . Never assume the hardware is in the same position it was when the power went out.
In Beckhoff TwinCAT, the First Scan Bit is accessed via the _TaskInfo system array using the FirstCycle property. This bit is uniquely TRUE during the first execution cycle of a task, allowing for precise system initialization. First Scan Bit - OpenPLC Forum