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Calling FBs & FCs in OB1 - Clarification

No, it is not always mandatory to call FBs and FCs directly within OB1. OB1 is the main cyclic execution block, but program organization doesn't *require* all logic to reside there.

Here's why you might see programs without direct FB/FC calls in OB1:

• Hierarchical Structure: FBs can call other FBs and FCs, creating a hierarchical structure. OB1 might only call a few 'top-level' FBs, which then manage the rest of the logic.
• Event-Driven Programming: Some FBs/FCs might be called indirectly through interrupts (OB35, OB36, etc.) or via hardware triggers, bypassing direct OB1 calls.
• Modularization: Breaking down the program into reusable FB/FC blocks improves maintainability and reduces complexity in OB1.

Best Practice: While not *required*, OB1 typically contains calls to FBs that perform essential, continuous tasks. However, a well-structured program will distribute functionality appropriately across multiple blocks.

For more detailed information, please refer to the Siemens documentation on OB1 and FB/FC organization: OB1 - Organization Block