A method and configuration system are used for producing an application-specific functional module from a predefined functional module for a programmable controller. In this context, a marking device is useable to mask out subfunctions of the predefined functional module, so that just the software code for those subfunctions which is required in order to satisfy the functionality of the application-specific functional module are readable into the programmable controller. In this case, it is simultaneously necessary to ensure that only that software code which is not imperatively required for calculating a result for at least one of the unmarked subfunctions is masked out and is therefore not read in.