Quick Tips RS232 Cable Pinouts

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 RS232 Cable Pinouts

RS-232 (Recommended Standard 232) is the standard for establishing serial data signals 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 or male 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 IN Secondary Carrier Detect. Only needed if second channel being used.
13   SCTS IN Secondary Clear to Send. Only needed if second channel being used.
14   STD OUT Secondary Transmit Data. Only needed if second channel being used.
15   DB OUT Transmit Clock (TCLK, TxCLK). Used only in Synchronous mode.
16   SRD IN Secondary Receive Data. Only needed if second channel being used.
17   DD IN Receive Clock (RCLK). Used only in Synchronous mode.
18   LL - Local Loopback
19   SRTS OUT Secondary 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 # Connects To 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
19 <--------> 19
20 <--------> 20
21 <--------> 21
22 <--------> 22
23 <--------> 23
24 <--------> 24
25 <--------> 25
 
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
9    
10    
11    
12    
13    
14    
15    
16    
17    
18    
19    
20 <--------> 6,8
21    
22 <--------> 22
23    
24    
25    
 
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
9    
10    
11    
12    
13    
14    
15 <--------> 17
16    
17 <--------> 15
18    
19    
20 <--------> 6,8,22
21    
22 <--------> 6,8,20
23 <--------> 23
24    
25    

DB9 to DB9 Cable Pinouts

Straight Through Cable
DB9   DB9
Pin # Connects To Pin #
1 <--------> 1
2 <--------> 2
3 <--------> 3
4 <--------> 4
5 <--------> 5
6 <--------> 6
7 <--------> 7
8 <--------> 8
9 <--------> 9
 
Null Modem Cable
DB9   DB9
Pin # Connects To Pin #
1 <--------> 4
2 <--------> 3
3 <--------> 2
4 <--------> 1,6
5 <--------> 5
6 <--------> 4
7 <--------> 8
8 <--------> 7
9 <--------> 9
 
Loopback Connector
DB9
Pin # Connects To Pin #
1 <--------> 4,6,9
2 <--------> 3
3 <--------> 2
4 <--------> 1,6,9
5 <--------> 5
6 <--------> 1,4,9
7 <--------> 8
8 <--------> 7
9 <--------> 1,4,6

DB9 to DB25 Cable Pinouts

Straight Through
DB9   DB25
Pin # Connects To Pin #
1 <--------> 8
2 <--------> 3
3 <--------> 2
4 <--------> 20
5 <--------> 7
6 <--------> 6
7 <--------> 4
8 <--------> 5
9 <--------> 22
 
Null Modem
DB9   DB25
Pin # Connects To Pin #
1 <--------> 20
2 <--------> 2
3 <--------> 3
4 <--------> 6,8
5 <--------> 7
6 <--------> 20
7 <--------> 5
8 <--------> 4
9 <--------> 22

DB9 and DB25 to RJ45 Cable Pinouts

There are many different ways to interconnect DB9 or DB25 with RJ45. The tables shown below represent just few examples that may not be applicable for your particular case.

Console Cable
DB9 DB25   RJ45
Pin # Pin # Connects To Pin #
1 8 <--------> 2
2 3 <--------> 3
3 2 <--------> 6
4 20 <--------> 7,8
5 7 <--------> 4
6 6 <--------> 2
7 4 <--------> 5
8 5 <--------> 1
9 22    
 
Cisco Console Cable
DB9 DB25   RJ45
Pin # Pin # Connects To Pin #
1 8    
2 3 <--------> 3
3 2 <--------> 6
4 20 <--------> 7
5 7 <--------> 4,5
6 6 <--------> 2
7 4 <--------> 8
8 5 <--------> 1
9 22    
 
Null Modem Cable
DB9 DB25   RJ45
Pin # Pin # Connects To Pin #
1 8 <--------> 3
2 3 <--------> 5
3 2 <--------> 6
4 20 <--------> 3
5 7 <--------> 4
6 6 <--------> 1,2
7 4 <--------> 8
8 5 <--------> 7
9 22