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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 #NameDirectionDescription
1 --Protective/Shielded Ground
23TDOUTTransmit Data (Tx, TxD)
32RDINReceive Data (Rx, RxD)
47RTSOUTRequest To Send
58CTSINClear To Send
66DSRINData Set Ready
75SGND-Signal Ground/Common Return
81CDINCarrier Detect (DCD)
9 --Reserved
10 --Reserved
11 --Unassigned
12 SDCDINSecondary Carrier Detect. Only needed if second channel being used.
13 SCTSINSecondary Clear to Send. Only needed if second channel being used.
14 STDOUTSecondary Transmit Data. Only needed if second channel being used.
15 DBOUTTransmit Clock (TCLK, TxCLK). Used only in Synchronous mode.
16 SRDINSecondary Receive Data. Only needed if second channel being used.
17 DDINReceive Clock (RCLK). Used only in Synchronous mode.
18 LL-Local Loopback
19 SRTSOUTSecondary Request to Send. Only needed if second channel being used.
204DTROUTData Terminal Ready
21 RL/SQ-Signal Quality Detector/Remote loopback
229RIINRing Indicator
23 CH/CIOUTSignal Rate selector
24 DA-Auxiliary Clock (ACLK). Secondary Channel only.
25 --Unassigned
DB25 to DB25 Cable Pinouts
Straight Through Cable
DB25 DB25
Pin #Connects ToPin #
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 ToPin #
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 ToPin #
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 ToPin #
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 ToPin #
1<-------->4
2<-------->3
3<-------->2
4<-------->1,6
5<-------->5
6<-------->4
7<-------->8
8<-------->7
9<-------->9
 
Loopback Connector
DB9
Pin #Connects ToPin #
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 ToPin #
1<-------->8
2<-------->3
3<-------->2
4<-------->20
5<-------->7
6<-------->6
7<-------->4
8<-------->5
9<-------->22
 
Null Modem
DB9 DB25
Pin #Connects ToPin #
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
DB9DB25 RJ45
Pin #Pin #Connects ToPin #
18<-------->2
23<-------->3
32<-------->6
420<-------->7,8
57<-------->4
66<-------->2
74<-------->5
85<-------->1
922  
 
Cisco Console Cable
DB9DB25 RJ45
Pin #Pin #Connects ToPin #
18  
23<-------->3
32<-------->6
420<-------->7
57<-------->4,5
66<-------->2
74<-------->8
85<-------->1
922  
 
Null Modem Cable
DB9DB25 RJ45
Pin #Pin #Connects ToPin #
18<-------->3
23<-------->5
32<-------->6
420<-------->3
57<-------->4
66<-------->1,2
74<-------->8
85<-------->7
922