Abstract: A data line interface for coupling an RS-232 line to a coaxial cable line, and for coupling a coaxial cable line to an RS-232 line is disclosed. The interface is responsive on the RS-232 side to a request to send (RTS) signal and a data signal (TXD) to couple the data signal to the coax line. Data signals received on the coax line provide a data signal (RCD) and carrier detect outputs on the RS-232 side of the interface. The interface is capable of asynchronous full duplex communication at 9600 baud or greater, and capable of effectively coupling two RS-232 compatible devices together in a manner which is transparent to the devices.