To enable the class 1 master (the controller) to communicate efficiently with a slave, it must know how many bytes the master will send the slave as outputs and how many bytes it will receive as inputs. This is defined in the configuration.
The possible configurations of a DP slave are defined in the GSD file. The current cefault configuration can also be read by the DP master from the DP slave with a Get_Configuration telegram. Before the DP slave can exchange payload data with a DP master, the valid configuration must be confirmed by the DP master to the DP slave with the Chk_Configuration telegram.