EIA-232

communications, standard (Formerly "RS-232") The most common

asynchronous serial line standard. EIA-232 is the EIA

equivalent of ITU-T V.24, and V.28.

EIA-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 7) and one for

data in each direction. The other pins are primarily 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 DataCommunications Equipment (DCE) or Data Terminal Equipment

(DTE). DTE receives data on pin 3 and transmits on pin 2

(TD). A DCE EIA-232 interface has a female connector. DCE

receives data from DTE on pin 2 (TD) and sends that data out

the analog line. Data received from the analog line is sent

by the DCE on pin 3(RD).

Originally DCE was a modem and DTE was a computer or terminal.

The terminal or computer was connected (via EIA-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 common, however, to find equipment with the wrong sex

connector or with pins two and three reversed, requiring the

insertion of a cable or adaptor wired as a gender mender or

null modem. Such an adaptor is also required when

connecting a computer directly to a terminal or to another

computer without the use of modems.

(1999-12-28)