The 73M223 modem device receives and transmits serial and binary data over existing telephone networks using Frequency Shift Keying (FSK). It provides the filtering, modulation, and demodulation to implement a serial, asynchronous data communication channel. The 73M223 employs the CCITT V.23 signaling frequencies of 1302 and 2097 Hz, operating at 1200 baud, and is intended for half duplex operation over a two-line system.