<communications, standard> The most common asynchronous serial line standard. RS-232 is the EIA equivalent of ITU-T V.24 and V.28.
RS-232 specifies the gender and pin use of connectors, but not their physical type. RS-423 specifies the electrical signals. 25-way D-type connectors are common but often only three wires are connected - one ground (pin seven) and one for data in each direction. The other pins are mostly related to hardware handshaking between sender and receiver and to carrier detection on modems, inoperative circuits, busy conditions etc.
The standard classifies equipment as either Data Communications Equipment (DCE) or Data Terminal Equipment (DTE). A DCE RS-232 interface should have a female connector and should transmit on pin two and receive on pin three. DTE should have a male connector and should should transmit on pin three (TD) and receive on pin two (RD). Originally DCE was a modem and DTE was either a computer or a terminal. The terminal and computer were connected (via RS-232) to two modems, which were connected via a telephone line.
The above arrangement allows a computer or terminal to be connected to a modem with a straight-through (2-2, 3-3) cable. It is not uncommon though to find equipment with the wrong sex connector and/or with pins two and three the wrong way round, requiring the insertion of a cable or adaptor wired as a gender mender or null modem. Such a cable is also required when connecting a computer directly to a terminal or to another computer when not using modems.
(24 Dec 1995)