Resetting Modbus, OPC UA, or TCP/IP communication buffers to ensure stale data isn't transmitted during boot-up.
Use a local BOOL := TRUE; variable and clear it at the end of the IF statement. Use TwinCAT_SystemInfoVarList._TaskInfo[x].CycleCount = 1 . HMI Safe-State
// Your logic here... IF bFirstScan THEN // Initialization code END_IF // Last line of the program bFirstScan := FALSE; Use code with caution. Copied to clipboard beckhoff first scan bit
IF bIsFirstScan THEN // Your one-time initialization code bIsFirstScan := FALSE; // Flag is cleared for future scans END_IF
IF TwinCAT_SystemInfoVarList._FirstScan THEN // One-time actions END_IF Resetting Modbus, OPC UA, or TCP/IP communication buffers
Do not call asynchronous function blocks (like file I/O operations, ADS read/write blocks, or socket communications) inside the first scan IF statement. These blocks require multiple PLC cycles to return a bBusy = FALSE status. They will stall or fail if executed only once.
This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later. HMI Safe-State // Your logic here
The cleanest, most standard-compliant way to create a first scan bit in TwinCAT is by using a local BOOL variable that defaults to FALSE (or TRUE depending on your logic preference).