An additional benefit brought by the use of FB - Database & Sql Blog Articles

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When using function blocks (FBs), you can set initial values for local variables (excluding TEMP) stored in the instance DB of the FB. If a variable needs to be initialized with its default or initial value, there's no need to explicitly assign it when calling the FB. For example, if the initial values are defined in OB100, you can call the FB later without specifying the variable values again. In this case, the system will use either the initial value set in OB100 or the last executed value from the instance DB. This helps maintain consistency and reduces redundant configuration.

Unlike FBs, function calls (FCs) don’t have a dedicated storage area for their internal variables. Therefore, when calling an FC, you must assign values to all formal parameters. This makes FCs more rigid but also more straightforward in terms of parameter handling. Using FBs allows users to manage a large number of parameters more efficiently. For example, in complex function blocks like the PID controller (FB41), the user can significantly reduce the effort required to set up parameters each time the block is called. This feature is especially useful in applications where many parameters are involved and need frequent adjustments.

Overall, understanding the difference between FBs and FCs is crucial for efficient programming in systems like Siemens S7. By leveraging the power of FBs, developers can streamline their code, improve reusability, and minimize errors caused by manual parameter input. Whether you're working on a simple control task or a sophisticated automation system, choosing the right approach—whether FB or FC—can make a big difference in both development time and system performance.