Abstract: A digital serial interface system is provided for communicating digital signals including digitized audio between microprocessor-based Control and Transceiver Units of two-way radio communications equipment. The system of the invention essentially comprises three subsystems: (1) an interface in the microprocessor-based Control Unit, (2) an interface in the microprocessor-based Transceiver Unit and (3) a two-way medium for linking the two units. Various signals and audio in the Control Unit interact with a software-driven microprocessor of the Control Unit and are digitized and then translated into a serial format, organized in channel groups through a TDM (Time Division Multiplex)/PCM (Pulse Code Modulation) process and transmitted in frames through a two-way medium to the Transceiver Unit which is also microprocessor-based and incorporates a similar interface. The digital data communicated to the Transceiver Unit then undergoes a reverse process. The Interface System is duplex (bidirectional).