EIA-232

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 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.

RS-232

(Recommended Standard-232) A TIA/EIA standard for serial transmission. Although employed for numerous other purposes, the RS-232 serial port was widely used on earlier personal computers prior to USB (see serial port). The RS-232 cable limitation of 50 feet can be extended to several hundred feet with high-quality cable.

Although RS-232 defines the signals for 25 lines, many applications use less than a dozen, which is why both DB-25 and DB-9 connectors are used. RS-232 transmits positive voltage for a 0 and a negative voltage for a 1. In 1984, RS-232 was officially renamed TIA/EIA-232-E. See RS-232/485.

Pin Settings for Plug(Reverse order for socket.)
  ______________________________________
  1  2  3  4  5  6  7  8  9  10 11 12 13
   14 15 16 17 18 19 20 21 22 23 24 25

           _________________
             1  2  3  4  5
               6  7  8  9


 25 pin                        9 pin

  1 - PG   Protective ground
  2 - TD   Transmitted data     3
  3 - RD   Received data        2
  4 - RTS  Request to send      7
  5 - CTS  Clear to send        8
  6 - DSR  Data set ready       6
  7 - SG   Signal ground        5
  8 - CD   Carrier detect       1
  9 - + voltage (testing)
 10 - - voltage (testing)
 11 - 
 12 - SCD  Secondary CD
 13 - SCS  Secondary CTS
 14 - STD  Secondary TD
 15 - TC   Transmit clock
 16 - SRD  Secondary RD
 17 - RC   Receiver clock
 18 - 
 19 - SRS  Secondary RTS            9 pin
 20 - DTR  Data terminal ready      4
 21 - SQD  Signal quality detector
 22 - RI   Ring indicator           9
 23 - DRS  Data rate select
 24 - XTC  External clock
 25 - 
References in periodicals archive ?
When using a phone modem, the meters and IDRs can be "daisy-chained" with the EIA-485 cabling and then converted to EIA-232 to connect with the modem.
A rear serial communications port is available as either an EIA-232 or an EIA-485 interface.
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Each LCE-16 module provides for up to 16 software-selectable asynchronous and/or synchronous circuits operating between 75 bps and 64 kbps over EIA-232, X.21, V.35, or EIA-530 interfaces.
Included are two built-in EIA-232 ports and an expansion port which can be configured at EIA 232, EIA 422/485, radio modem, leased-line modem, or dial-up modem using a plug-in communications card.
The terminal can be equipped with two EIA-232, -422 or -485 serial ports; Ethernet 10Base-T or a Power-over-Ethernet (IEEE 802.3af) interface.
Qterm-G75 is an Ethernet-enabled graphics terminal that features a large 640 x 480 color TFT graphics LCD, 10 Base-T Ethernet with TCP/IP support, a touch screen with optional PS/2 keyboard connection, and EIA-232, -422 or -485 serial interface.
It comes equipped with one switch-selectable serial port and can communicate via EIA-232, EIA-422 or EIA-485.