The PD9903 is a digital CODEC that can be used in analog subscriber circuits such as private branch exchangers (PBXs) and switching equipment for central offices. It features three of the functions required for analog subscriber circuits: 2W/4W conversion, CODEC supervision, and subscriber line supervision. Use of the PD9903 in combination with a BS-SLIC (PC7073) can reduce the number of components required in analog subscriber circuits.