A modem utilizing a DAA having line side circuitry including a telephone network interface and system side circuitry including a host system interface. The line side circuitry and the system side circuitry are separated by a high voltage isolation barrier. In accordance with the invention, the high voltage isolation barrier and other DAA circuitry are configured such that data and control information may be communicated between the system side circuitry and the line side circuitry using a serialized digital communication protocol. In one embodiment of the invention, the line side circuitry of the modem includes detection and measurement circuitry that is programmable to measure or establish electrical characteristics (e.g., tip/ring voltage and loop current) of the telephone line interface connection. Command information for the programmable circuitry is multiplexed with data communicated across the high voltage isolation barrier. Interrupt signals and information for synchronizing communications between the system side circuitry and the line side circuitry may also comprise a portion of the serialized datastream.