The CT1555-3/CT1820 Bit Processor Unit (BPU) is an advanced Hybrid Microcircuit that provides the interface between a MIL-STD-1553 Transceiver such as CT3231M or CT3232M, and the subsystem internal parallel data bus. The unit can be employed as the mux bus interface for Remote Subsystems or Master Terminal Bus Controllers, thus providing a common interface for all systems communicating over the bus. The unit places no restrictions on Command, Response or polling operations as it transfers all Command, Status and Data words from the bus to parallel output lines, together with error information, bus status and handshaking signals. It also contains 5 Bit Address Recognition, Broadcast and Mode Code Decode, Terminal Fail Safe Signal and Self Test. In the transmit mode, it accepts parallel data from the user and transmits Command, Status and Data words, under subsystem control, to the data bus. Positive handshaking signals provide logic control synchronisation between the unit and the subsystem for direct data flow. The hybrid is completely compatible with all the electrical and functional spec requirements of MIL-STD-1553 A & B.