(
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 -