Source : Free On-Line Dictionary of Computing

EIA-232
     
         (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 {Data
        Communications 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)