4-Wire Interface with Call Signal, Matrix-to-Partyline The EF-701M interface converts a single channel of standard or TW partyline intercom to four-wire audio, while also converting call signals to RS-422 data (and back). The resulting four-wire audio plus RS-422 data can then be sent to a Clear-Com Matrix port, fiber-optic converter (modem) or connected to another EF-701M over twisted-pair cable such as CAT-5E.