Beckhoff First Scan Bit Repack Info

Another method, often considered more accurate for truly catching the first PLC tick after the system is fully booted and ready, involves using the TwinCAT system library functions if needed, but the method above is generally robust for most applications.

// Startup timer after first scan IF NOT fbFirstScan.bFirstScan AND NOT bStartupComplete THEN tStartupTimer(IN:=TRUE, PT:=T#2S); IF tStartupTimer.Q THEN bStartupComplete := TRUE; // Enable normal operation END_IF END_IF

Declare a global boolean, e.g., bFirstScan : BOOL := TRUE; . beckhoff first scan bit

Remember that the first scan bit is a tool, not a complete solution. For complex systems, combine it with other initialization techniques like FB_init methods, state machines, and proper variable typing to create truly robust automation code. Test your initialization logic thoroughly on your specific target hardware, as subtle differences between platforms can lead to unexpected behavior in production environments.

Which of these two methods are you planning to use for your specific project? Beckhoff CX1010 first scan | PLCtalk - Interactive Q & A Another method, often considered more accurate for truly

METHOD FB_init : BOOL VAR_INPUT bInitRetains : BOOL; // If TRUE, retain variables are initialized bInCopyCode : BOOL; // If TRUE, instance was copied (e.g., during online change) END_VAR // Initialization code here nTargetVelocity := 1500; bEnableAxis := TRUE; Use code with caution. Why Use It?

TwinCAT provides system variables via its standard libraries that can detect system startup conditions. Implementation For complex systems, combine it with other initialization

Without a mechanism to detect the first scan, your program would execute initialization logic (like setting default values, clearing counters, or resetting state machines) every single time the code runs. Key scenarios requiring the First Scan Bit include:

Implementation Method 3: Using the TwinCAT 3 Event Functions

When you instantiate a function block, TwinCAT automatically calls its FB_Init method once.

Do you need the logic to survive an , or only a full PLC Restart ? Share public link