| Device signal | D-Sub9 plug | Device or modem signal | D-Sub9 plug |
|---|---|---|---|
| TxD | 3 | RxD | 2 |
| RxD | 2 | TxD | 3 |
| RTS | 7 | CTS | 8 |
| CTS | 8 | RTS | 7 |
| DTR | 4 | DCD | 1 |
| DCD | 1 | DTR | 4 |
| GND | 5 | GND | 5 |
| Operating a modem over the serial interface | |
| Device signal | D-Sub9 plug | Device or modem signal | D-Sub9 plug |
|---|---|---|---|
| TxD | 3 | RxD | 2 |
| RxD | 2 | TxD | 3 |
| RTS | 7 | CTS | 8 |
| CTS | 8 | RTS | 7 |
| DTR | 4 | DCD | 1 |
| DCD | 1 | DTR | 4 |
| GND | 5 | GND | 5 |