A once widely used standard interface covering the electrical connection between data communication equipment, such as a modem, and data terminal equipment, such as a microcomputer or computer terminal. The RS232C interface standard was developed by the EIA (Electronic Industries Association) and is essentially equivalent to the CCITT’s V24 interface; RS232A and RS232B were earlier superseded versions of the specification.

In 1975 the EIA introduced two new specifications in order to upgrade system capabilities: the RS423 interface, which closely resembles RS232C, and the RS422 and RS485 interfaces, both of which allow higher transmission rates. RS232C operates with a single transmitter and single receiver per channel up to about 20 metres. RS423, RS422, and RS485 operate at up to about 1200 metres at higher speeds and support multiple transmitters and receivers in each channel. RS422 and RS485 operate in differential mode using balanced cables. These interfaces are now being phased out having been largely replaced by USB.