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A null modem is a device that allows one to connect two computers together, typically with only a serial port. No networking hardware such as a NIC or a modem are required for this.
Null modem cable
Also known as a RS-232 cable, a null modem cable is a specially designed cable that allows a user to connect two computers directly to each other via their communications ports (RS-232 ports). Null modems are particularly useful with portable computers because they enable the portable computer to exchange data with a larger system (i.e. a desktop computer or desknote).
Null modem cable pin mapping
This is the most common pin mapping, one common variant is to also connect pins 1 and 6
| 9 pin to 9 pin |
| CD | 1 | 1 |
| RD | 2 | 3 |
| TD | 3 | 2 |
| DTR | 4 | 6 |
| Ground | 5 | 5 |
| DSR | 6 | 4 |
| RTS | 7 | 8 |
| CTS | 8 | 7 |
| - | 9 | 9 |
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| 9 pin to 25 pin |
| 1 | 8 |
| 2 | 2 |
| 3 | 3 |
| 4 | 6 |
| 5 | 7 |
| 6 | 20 |
| 7 | 5 |
| 8 | 4 |
| 9 | 22 |
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Here is another pin connection diagram for a null modem:
See also
External links
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