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Quick Tips RS232 Cable Pinouts
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RS232 Cable Pinouts
RS-232 (Recommended Standard 232) is the standard for
establishing serial datasignals connection between DTE (Data
Terminal Equipment) and DCE (Data Circuit-
terminating Equipment). For over 40 years this standard is
commonly used in
computers, networking and telecommunication. A similar ITU-T
standard is V.24.
Detailed description of the standard is available from Wikipedia
and many other
sources in the Internet. This page provides only the list of
signals used in RS232 and
pinouts of most commonly used types of serial cables.
In all the cases the length of the cable should not exceed 25
feet (about 7.5 meters)
unless a signal booster is used. Most commonly used types of
serial cable connectors
are 9-pin connector DB9 and 25-pin connector DB25. Each of them
can be of female ormale type as shown on the following image.
Signal Names and Descriptions
DB25
Pin #
DB9
Pin #Name Direction Description
1 - - Protective/Shielded Ground
2 3 TD OUT Transmit Data (Tx, TxD)
3 2 RD IN Receive Data (Rx, RxD)
4 7 RTS OUT Request To Send
5 8 CTS IN Clear To Send
6 6 DSR IN Data Set Ready
7 5 SGND - Signal Ground/Common Return
8 1 CD IN Carrier Detect (DCD)
9 - - Reserved
10 - - Reserved
11 - - Unassigned
12 SDCD INSecondary Carrier Detect. Only needed if second
channel being used.
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13 SCTS INSecondary Clear to Send. Only needed if second
channel being used.
14 STD OUTSecondary Transmit Data. Only needed if second
channel being used.
15 DB OUTTransmit Clock (TCLK, TxCLK). Used only in
Synchronous mode.
16 SRD INSecondary Receive Data. Only needed if second
channel being used.
17 DD INReceive Clock (RCLK). Used only in
Synchronous mode.
18 LL - Local Loopback
19 SRTS OUTSecondary Request to Send. Only needed if
second channel being used.
20 4 DTR OUT Data Terminal Ready
21 RL/SQ - Signal Quality Detector/Remote loopback
22 9 RI IN Ring Indicator
23 CH/CI OUT Signal Rate selector
24 DA -Auxiliary Clock (ACLK). Secondary Channel
only.
25 - - Unassigned
DB25 to DB25 Cable Pinouts
Straight Through
Cable
DB25 DB25
Pin # ConnectsTo Pin #
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9
10 10
11 11
12 12
13 13
14 14
15 15
16 16
17 17
18 18
Null Modem Cable
DB25 DB25
Pin #Connects
To
Pin #
1
2 3
3 2
4 5
5 4
6 8,20
7 7
8 6,20
910
11
12
13
14
15
16
17
1819
Loopback Connector
DB25
Pin
#
Connects
To
Pin #
1
2 3
3 2
4 5
5 4
6 8,20,22
7 7
8 6,20,22
910
11
12
13
14
15 17
16
17 15
1819
