You would need the following to configure the S5 side:
IM308-C Profibus-DP module (6ES5-308-3UC21)
Flash EPROM (6ES5-374-1KH21)
In S5-115U racks, an adapter casing (6ES5491-0LB11)
COM Profibus V5.1 software
USB Prommer (or Siemens PG with Prom burner)
Profibus cable and connectors for the PLC to PLC connection.
The USB Prommer or Siemens PG is required to write to the FLASH Memory card for the IM308C, which you configure with COM Profibus.
Make sure you have enough unused I/O (P) area to handle the amount of information you need to exchange. If you need a larger amount of information, it is better to make the IM308C be the Profibus-DP master, and get a Controllogix Profibus-DP slave module. With the IM308C as the master, it is possible to exchange up to 400 bytes of total information with the Prosoft Profibus DP slave module (max. 244 bytes input and max. 244 bytes output, but the total not more than 400 bytes).... and it is possible to read/write the data without using I/O memory areas in the S5.