Beckhoff First Scan Bit Portable [FAST]

| Do | Don't | |----|-------| | Use FB_FirstScan from Tc2_System | Rely on manual := TRUE flags | | Keep first scan logic short | Put heavy processing inside first scan | | Set outputs to safe defaults | Assume all retentive data is valid | | Combine with Tc2_Standard for consistent behavior | Use first scan for normal logic flow |

🚀 Ensures that PID gains, speed limits, or timers start with default "safe" values rather than zeros. beckhoff first scan bit

If you need a bit that resets every time you "Stop" and "Start" the PLC program (warm restart), the standard practice is to create a non-persistent variable that defaults to TRUE and is set to FALSE at the end of the scan. | Do | Don't | |----|-------| | Use

Built-in FirstScan flag (recommended if provided) Copied to clipboard The First Scan Bit is

VAR_GLOBAL bIsFirstScan : BOOL := TRUE; // Starts TRUE when the PLC runtime begins END_VAR Use code with caution. Copied to clipboard

The First Scan Bit is the "ignition switch" of a TwinCAT program. By isolating startup logic into this single-cycle window, engineers ensure that the system begins its operation from a known, predictable state

bFirstScanSys := TwinCAT_SystemInfoVarList._FirstScan;