This cable should be used for DTE to DCE (for instance computer to modem) connections with hardware handshaking.
 |
DB9 pin D-SUB female to the PC |
 |
DB25 pin D-SUB male to the modem |
| Female | Male | Direction | |
|---|---|---|---|
| Shield | 1 | ||
| Transmit Data | 3 | 2 | → |
| Receive Data | 2 | 3 | ← |
| Request to Send | 7 | 4 | → |
| Clear to Send | 8 | 5 | ← |
| Data Set Ready | 6 | 6 | ← |
| System Ground | 5 | 7 | |
| Carrier Detect | 1 | 8 | ← |
| Data Terminal Ready | 4 | 20 | → |
| Ring Indicator | 9 | 22 | ← |
Null modem (crossed) cable DB9 connectors
Null modem (crossed) cable DB9 and DB25 connectors
Null modem (crossed) cable DB25 connectors
Modem (straight) cable (DB25-DB25)