Beckhoff First Scan Bit -

The First Scan Bit is a that is TRUE only for a single PLC cycle immediately after the runtime system starts executing the application. On the second cycle, it becomes FALSE and remains FALSE until the next controller reboot or program download.

This system variable is automatically managed by the TwinCAT runtime. beckhoff first scan bit

Have a tricky Beckhoff initialization issue? Share your experience in the comments or contact your local Beckhoff automation partner. The First Scan Bit is a that is

// -- Reset the first scan trigger for next init -- bInit := FALSE; Have a tricky Beckhoff initialization issue

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 .

The most reliable way to detect the first scan in TwinCAT 3 is to use the structure . Every task has an associated system structure that includes a FirstCycle boolean . Example Implementation (Structured Text):

To use the First Scan Bit in a Beckhoff PLC, you need to access the PLC's system variables. The First Scan Bit is typically represented by a specific system variable, such as FirstScan or InitDone .