Beckhoff First Scan Bit Fixed (PC)

Without FirstScan , you face several classic initialization hazards:

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:

By utilizing the standard initialization behavior of variables in TwinCAT, you can create a self-resetting flag. beckhoff first scan bit

If you have multiple programs ( MAIN , Safety , HMI ), ensure you know which program runs first to set the bFirstScan bit. It is usually best to handle initialization in the main task of your main program.

If your TwinCAT project has multiple tasks (e.g., a fast 1ms task and a slow 10ms task), remember that each task has its own "first cycle." Without FirstScan , you face several classic initialization

: You can manually create a non-retentive boolean variable initialized as How it works : Define a with an initial value of

No manual coding is required to reset the bit; it is inherently tied to the task execution. 2. Manual Logic (The Classic Way) Name the method exactly FB_init

It is cleaner to have one IF bFirstScan block at the beginning of your code rather than scattering multiple IF bFirstScan blocks throughout your program, which can make debugging difficult. 4. First Scan Bit vs. PLC_PRG_Init

When designing your initialization routines within the first scan window, adhere to the following architectural rules: