IF NOT bInitialized THEN // Initialization code here bInitialized := TRUE; END_IF Use code with caution. Copied to clipboard
TwinCAT controllers have distinct boot phases. The first scan bit is set during the transition from to RUN mode. Understanding this can help diagnose why certain initialization tasks might not execute as expected. The SystemTaskInfoArr[1].firstCycle variable will be TRUE during this transition, but not during a simple program restart from the development environment. beckhoff first scan bit
| Variable Type | Behavior on Power Cycle | Behavior on Program Download | Interaction with First Scan | |---|---|---|---| | | Re-initializes to declared start value | Re-initializes | First scan can set custom initial values | | RETAIN | Retains last value from before power loss | Retains last value (by default) | Useful for detecting first scan without losing value | | PERSISTENT | Retains value across program changes | Retains value across program downloads | Often used with first scan to determine if first run after major update | IF NOT bInitialized THEN // Initialization code here
This mechanism is essential for several key initialization tasks that should occur only once when the controller powers up or is restarted: beckhoff first scan bit
Are you handling during this first scan?
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