Beckhoff First Scan Bit -

Even experienced programmers can make mistakes. Here are some pitfalls to watch out for.

When a PLC starts up, all variables are typically initialized to their default values (usually

// This runs once when the FB is created (first scan of the FB) METHOD FB_Init : BOOL VAR_INPUT bInitRetains : BOOL; // TRUE if retain variables are restored bInCopyCode : BOOL; // TRUE if FB is copied END_VAR fSpeed := 0.0; // Initialize internal variable bReady := FALSE; END_METHOD beckhoff first scan bit

Clear old error flags that might have occurred during the previous shutdown. Establish Communication:

: In large OOP-based TwinCAT projects with many reusable function blocks. Even experienced programmers can make mistakes

If you cannot use PlcTaskSystemInfo , you can create a local BOOL variable that is initialized to TRUE .

. The first scan bit should typically be used to compliment these memory features, not fight against them. Conclusion The first scan bit should typically be used

PROGRAM MAIN VAR fbFirstScan : FB_FirstScan; bInitDone : BOOL; END_VAR

The PlcTaskSystemInfo structure is defined to include the crucial firstCycle boolean, as well as other helpful diagnostic and monitoring variables. A PlcTaskSystemInfo object provides the following fields:

The Beckhoff First Scan bit is an essential tool for creating robust, predictable automation systems. By utilizing _TaskInfo[index].FirstCycle 1.2.4, you ensure your machine powers up safely and consistently.

(without download) → Counter does not increment (warm start without new program) → In many cases, bFirstScan stays FALSE here unless configured to detect warm starts.