Null Modem Cable Specification
Updated September 16, 2002
Created September 21, 2001

Autogenerated Site Map
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Signal Name DB-25 Pin DB-9 Pin   DB-9 Pin DB-25 Pin  
FG (Frame Ground) 1 - X - 1 FG
TD (Transmit Data) 2 3 - 2 3 RD
RD (Receive Data) 3 2 - 3 2 TD
RTS (Request To Send) 4 7 - 8 5 CTS
CTS (Clear To Send) 5 8 - 7 4 RTS
SG (Signal Ground) 7 5 - 5 7 SG
DSR (Data Set Ready) 6 6 - 4 20 DTR
CD (Carrier Detect) 8 1 - 4 20 DTR
DTR (Data Terminal Ready) 20 4 - 1 8 CD
DTR (Data Terminal Ready) 20 4 - 6 6 DSR

Only 9 wires are used in the configuring of the null modem cable; however, there is no connection to pin #9. Both pins 1 & 6 on the first connector are attached to pin #4 on the second connector. Likewise, pin #4 on the first connector is attached to both pins 1 & 6 on the second connector.

 

Null Modem Wiring Diagram

If a table is worth 100 words, then a picture must be worth 1000 words:

Null Modem Wiring Diagram

Resources

http://www.nullmodem.com/NullModem.htm
http://www.loop-back.com/null-mod.html
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