You can declare the methods explicitly in order to influence the initialization of function block variables, as well as the behavior when exiting function blocks.

‎FB_Init‎ is always available implicitly and it is used primarily for initialization. For a specific influence, you can also declare the methods explicitly and provide additional code there with the standard initialization code.

‎FB_Reinit‎ has to be implemented explicitly. If this method exists, then it is called after the instance of the affected function block is copied. That happens during an online change after changes to the function block declaration (signature change) in order to reinitialize the new instance module. To reinitialize the basic implementation of the function block, you have to call ‎FB_Reinit‎ explicitly.

‎FB_Exit‎ must be implemented explicitly. If there is an implementation, then the method is called before the controller removes the code of the function block instance (implicit call).

The following shows some use cases of these methods for different operating conditions.