From The Free On-line Dictionary of Computing: (http://www.foldoc.org/, Editor Denis Howe)
(Formerly "RS-485") An EIAserial linestandard which specifies 2-wire, half-duplex, differential line, multi-point communications. Maximum cable length is 1200m. Maximum data rates are 10Mbps at 1.2m or 100Kbps at 1200m. EIA-485 can implement a truly multi-point communications network, and specifies up to 32 drivers and 32 receivers on a single (2-wire) bus.