AFAIK c-bus works with "normal" serial data at 300-9600 bps with 9600 being the recommended speed.
It's a full ISO 7 layer protocol which seems something of an overkill.
Despite me having what appears to be a comprehensive set of documentation PDFs I'm buggered if I can see what the PHY layer is.
C-Bus supports a number of interfaces such as RS232 and TCP/IP
These of course are two totally different and non-comparable things so that's not much help.
cable lengths up to 1000 meter using Cat-5 cable
This implies RS-485, no way RS-232 will do this.
Anyway if you can figure out how to connect to the PHY layer it should be easy to sniff the data with a serial port, the protocol is well documented.