RS-232

RS-232

(Recommended Standard-232) A TIA/EIA standard for serial transmission between computers and peripheral devices (modem, mouse, etc.). Using a 25-pin DB-25 or 9-pin DB-9 connector, its normal cable limitation of 50 feet can be extended to several hundred feet with high-quality cable.

RS-232 defines the purpose and signal timing for each of the 25 lines; however, many applications use less than a dozen. RS-232 transmits positive voltage for a 0 bit, negative voltage for a 1. In 1984, this interface was officially renamed TIA/EIA-232-E standard (E is the current revision, 1991), although most people still call it RS-232.

               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 - 

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RS-232

(communications)

A standard developed by the Electronic Industries Association that governs the interface between data processing and data communications equipment, and is widely used to connect microcomputers to peripheral devices.

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RS-232 - EIA-232