This is a port-powered, two-channel RS-232 to RS-422 converter. It converts TD and RD RS-232 lines to balanced RS-422 signals. The unit is powered from the RS-232 handshake lines DTR and RTS. Only one of these lines must be present, and the unit will work regardless of whether the lines are high or low. Both the RS-422 driver and receiver are enabled at all times.