RS232 Modem Cable Layout (2-wire, DB9-DB25)
This cable should be used for DTE to DCE (for instance computer to modem) connections without hardware handshaking.
 | DB9 pin D-SUB female to the computer |
 | DB25 pin D-SUB male to the modem |
| Female | Male | Direction | |
|---|---|---|---|
| Shield Ground | 1 | ||
| Transmit Data | 3 | 2 | → |
| Receive Data | 2 | 3 | ← |
| System Ground | 5 | 7 | |
| Jumper these: | |||
| Request to Send | 7 | ← | |
| Clear to Send | 8 | ← | |
| Data Set Ready | 6 | ← | |
| Carrier Detect | 1 | ← | |
| Data Terminal Ready | 4 | → | |
| Request to Send | 4 | → | |
| Clear to Send | 5 | ← | |
| Data Set Ready | 6 | ← | |
| Carrier Detect | 8 | ← | |
| Data Terminal Ready | 20 | → | |
Full modem cable (DB9-DB25) with hardware handshaking
Two-wire modem cable (DB25-DB25)
RS232 connector pinouts (DB9, DB15, DB25, RJ45)