Beckhoff First Scan Bit Extra Quality Jun 2026

Are you working on a new project or troubleshooting an existing one? Do you need help with or TwinCAT 3 specifically? Let me know, and I can tailor the next guide to your needs. Share public link

Use TwinCAT's Watch Windows and Scope functionality to monitor your first scan variables in real-time, ensuring they behave as expected across all start-up scenarios.

If you use a manual first scan bit, ensure it is set to FALSE at the very end of your program. If you do it at the top, the rest of your logic won't see the TRUE state. beckhoff first scan bit

Name it something like GVL_System : VAR_GLOBAL bFirstScan : BOOL := TRUE; END_VAR Use code with caution. 2. Evaluate it at the start of your main code

FB_init is a specialized method you can add to any Function Block. It executes automatically before the PLC task starts its cyclic execution. Right-click your Function Block →right arrow →right arrow Method . Name the method exactly FB_init . It automatically generates the required signature: Are you working on a new project or

For modern TwinCAT 3 development utilizing Object-Oriented Programming (OOP), using a simple boolean flag inside a Function Block (FB) is often inefficient. Instead, Beckhoff supports the implicit FB_init method. Implementation

: This method is portable across different PLC brands and doesn't require specific TwinCAT system function calls. Example Implementation: Share public link Use TwinCAT's Watch Windows and

Without a proper first scan routine, your machine might start with actuators in unpredictable positions or unfinished states from a previous run.

The "Beckhoff first scan bit" is not a single feature but a concept implemented through various patterns. For simple projects, a F_TRIG on a TRUE variable is sufficient. For robust, reusable code, use FB_Init in function blocks. For system-wide initialization that must run before cyclic logic, use the INIT section.

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:

In Beckhoff TwinCAT, first scan detection is achieved via the PlcTaskSystemInfo.FirstCycle