The Profibus DP protocol specifies that the device manufacturer provide a text file for every Profibus slave. Generally, this file has a .GSD extension although language-specific versions (.GSG for German, .GSE for English, .GSF for French, and so on) might be available. This file contains the maximum number of Profibus modules in the device configuration, the parameter values specified for each module, and the number of input and output bytes in the data exchange messages. The parameter values customize the device behavior. The Device Definition also contains the supported baud rates, timing information, fail safe behavior, and diagnostic error codes. The Device Definition resides in the DeltaV Library. The Device Definition describes how the device communicates, it does not describe the data semantics or data type. For each Profibus module the user configures signals that describe the I/O that the Slot (Profibus module) provides to the DeltaV system.