Null Modem Cable Specification
Updated September 21, 2001
Created September 21, 2001
| 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:
Resources
http://www.nullmodem.com/NullModem.htm
http://www.loop-back.com/null-mod.html
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