RS485 network can include up to 32 receivers and 32 transmitters. The maximum cable length is 1200 m. The most common topography for this standard is a half-duplex bus structure (allowing the transmission of signals in both directions but not simultaneously).
The differential transmission between the transmitter and the receiver eliminates the external interference affecting both signal lines. Maximum bandwidth is 35 Mb/s at a maximum distance up to 10 m and 100 kb/s at a distance of up to 1200 m.
In CCTV monitoring, RS485 is mostly used to control the rotary cameras and cameras with automatic zoom. Splitters with optical couplers are used to protect the device connected via a RS485 interface against overvoltage. They allow to use a star topology instead of a standard bus topology.
Fig. 1. Example ORS-8 and ORS-22 splitters with optical couplers.