Beckhoff First Scan — Bit

For more detailed technical documentation, you can always refer to the Beckhoff Information System which provides comprehensive insights into TwinCAT programming standards.

The "Beckhoff first scan bit" is not a single feature but a concept implemented through various patterns. For simple projects, a F_TRIG on a TRUE variable is sufficient. For robust, reusable code, use FB_Init in function blocks. For system-wide initialization that must run before cyclic logic, use the INIT section. beckhoff first scan bit

FUNCTION_BLOCK FB_DriveController VAR_INPUT bEnable : BOOL; END_VAR VAR_OUTPUT bReady : BOOL; END_VAR VAR fSpeed : REAL; END_VAR For more detailed technical documentation, you can always

The first scan bit is a fundamental concept for writing robust and predictable PLC programs in Beckhoff TwinCAT. Whether you choose the system variable SystemTaskInfoArr[1].firstCycle for standard cold-start initialization or a custom RETAIN flag for more control, understanding this feature will help you build more reliable automation systems. For robust, reusable code, use FB_Init in function blocks

In this example, the FirstScan system variable is used to execute an initialization code segment during the first scan cycle. Once the initialization is complete, the FirstScan bit is reset to FALSE.

. At the very end of your main program, set this variable to