Beckhoff First Scan Bit (2027)
When a PLC starts, variables often default to zero or their last persisted state. However, many industrial systems require a specific "safe state" or initial configuration before the main control loop takes over. The first scan bit acts as a system trigger , allowing programmers to: Set Initial Values:
: Essential for setting default values for retentive memory variables. beckhoff first scan bit
Add library: Tc2_System
:Place this line at the very bottom of your MAIN program or the last task to execute : When a PLC starts, variables often default to
: Place code at the very end of your main program that sets this bit to FALSE . Because the variable is initialized to TRUE , it remains so for the entire first scan before being permanently toggled off. Comparison and Review PlcTaskSystemInfo.FirstCycle Manual Custom Bit Reliability Native to TwinCAT; handles task-specific restarts. Highly reliable if implemented at the program's end. Complexity Requires calling GETCURTASKINDEX . Extremely simple to declare and use. Best Use Case Add library: Tc2_System :Place this line at the