RS-485 is a multipoint communications standard set by the Electronics Industry Alliance (EIA) and Telecommunications Industry Association (TIA). RS-485 supports several connection types, including DB-9 and DB-37. Because of lower impedance receivers and drivers, RS-485 supports more nodes per line than RS-422.
RS-485 is effective in applications with significant electrical interference (noise) requiring a long transmission distance. Thus, the standard is often used in industrial applications. It is as an inexpensive local area network (LAN) connection that allows multiple receivers to connect within a multidrop configuration. RS-485 does not include a communications protocol.
Data transmission rates range from 35 Mbps (up to 33 feet)-100 Kbps (up to 4,000 feet). Because star and ring configurations are not recommended, equipment installed along RS-485 transmission lines (known as nodes, stations or devices) are connected as series. However, if necessary, star or ring configurations may be accommodated with special star/hub repeaters.
RS-485 uses a two-wire twisted pair bus. Although not always required, RS-485, like RS-422, may be configured with four wires as full-duplex. With certain restrictions, RS-422 and RS-485 may be co-configured.
Additionally, the RS-485 specification is used by Small Computer System Interface (SCSI)-2 and SCSI-3. RS-485 also may be used to allow remote connectivity between PCs and remote devices.