In Siemens PLC programming, FB (Function Block) and FC (Function) blocks are both types of reusable code elements used to organize and structure the program. However, there are some key differences between the two:

  1. Function Block (FB):

    • Object-Oriented: FBs are more closely associated with object-oriented programming concepts. They encapsulate data and functionality into a single block, allowing for a modular and structured approach.
    • Data and Methods: FBs can contain both data (internal variables) and methods (executable code). This encapsulation makes them useful for creating reusable and structured code.
    • Instance Creation: FBs can be instantiated multiple times in a program, creating instances of the same functionality with different data sets. This supports code reusability and modularity.
    • Communication: Communication between instances of FBs can occur through input and output parameters.
  2. Function (FC) Block:

    • Executable Code: FC blocks primarily contain executable code (sequential or structured text). They are used when you need a sequence of operations without encapsulating data.
    • No Data Encapsulation: Unlike FBs, FCs don't encapsulate data. They are more focused on providing a set of procedural steps to perform a specific task.
    • Instance Creation: FCs can also be instantiated multiple times, but they don't encapsulate data, so each instance operates independently of the others.