rs-232

EIA-232
RS-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 {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)