If you wish to connect a PROFIBUS DP slave, e.g. a CPU, to an external master, you need the GSD file. On an S7 master you can configure this directly via HW Config.
You can procure the GSD files for Siemens products directly via the Internet if the information is not in the module catalog of HW Config:
You can reach the PROFIBUS GSD files: SIMATIC
in Entry ID 113652. The language is coded in the file designation, e.g. "xxxx.gse" stands for English. Please note how the order numbers of the CPUs, e.g. CPU 315, are assigned to the station types.
If you want to include the DP devices in the module catalog of HW Config, the GSD files must be stored on a data medium that you can access from STEP 7. How to do this is described in detail in Entry ID 2383630.