The Device Definition contains information about data length, it does not contain information about the data itself. For each Profibus module in the Library, you add Profibus module signals that contain information such as signal direction, data type and the location of the signal value within the module’s data.
You can configure module signals at the library level and at the physical network level.
Library Configuration - To save engineering time for similar devices, create default signals in the library. Configure the signals that are common to all instances of a module type. When you add a slot for that module type to a device, it is created with the signals defined for it in the library. (You can also create module signals at the physical device.)
Physical Network Configuration - Complete the configuration of the signal at the physical configuration level. Provide a description of the signal and associate it with a specific Device Signal Tag (DST).