Abstract: An intelligent communications coprocessor connects computer workstations to moderate-bandwidth (up to 2 megabits/second) digital communications services. In particular, such communications services include but are not limited to Integrated Services Digital Network (ISDN) or Private-Branch Exchange (PBX) communications facilities. The communications coprocessor takes advantage of certain host resources including, preferably, signal processing capabilities of the computer, the computer's power supply and a generalized, high-speed computer/ peripheral serial interface. System cost for digital communications over such communications facilities is therefore reduced. Furthermore, the communications coprocessor can be used to support the transmission of arbitrary real-time, synchronous data streams as encountered in voice and video transmission services. This capability is required for many applications including voice recognition, text-to-speech, and videoconferencing.