A terminal, a serial printer, or a serial port for another computer usually functions as a DTE device. The Digi adapter is also a DTE device. To connect a DTE device to another DTE device a null modem cable or adapter must be used.
Two wires (one twisted pair) are required for each signal, a positive lead ("+"), and a negative lead ("-"). The "+" leads at one end of the cable must be connected to the "+" leads at the other end, and the "-" leads at one end must be connected to the "-" leads at the other end.
Incorrect wiring could result in damage to the connected devices. The following table shows the pin configurations for the EIA-422 versions of Digi DB-9 and DB-25 connectors.
| Signal | Description | DB-9 Pin | DB-25 Pin |
|---|---|---|---|
| TxD+ | Transmitted Data (+) | 8 | 2 |
| TxD- | Transmitted Data (-) | 9 | 14 |
| RxD+ | Received Data (+) | 6 | 3 |
| RxD- | Received Data (-) | 7 | 16 |
| RTS+ | Request To Send (+) | 2 | 4 |
| RTS- | Request To Send (-) | 3 | 19 |
| CTS+ | Clear To Send (+) | 4 | 5 |
| CTS- | Clear To Send (-) | 5 | 13 |
| GND | Chassis Ground | Shell | Shell |