The CT1775 Universal MACAIR/1553 Dumb Remote Terminal Unit (RTU) consists of a transceiver, and encoder/decoder, control logic, dual rank I/O registers and internal clock oscillator packaged in a 1.6" x 1.9" hermetic hybrid. It provides all the functions required to interface between a MACAIR (sinusodial) or MIL-STD-1553 (Trapezoidal) serial MUX data bus and a subsystem parallel 3-state data highway. Utilizing several ASIC ICs, the CT1775 provides sufficient handshaking, control and data lines to permit versatile operation as a remote terminal, a bus controller or a bus monitor, in either single or dual redundant data bus configurations. As a transmitter, the CT1775 accepts 8 bit or 16 bit parallel date from the subsystem, and outputs serial Manchester II coded Command, Status or Data words, under subsystem control. As a receiver, it accepts serial MIL-STD-1553 or MACAIR transmissions and transfers all Command, Status and Data words to the 8 bit or 16 bit data highway, under subsystem control. The CT1775 also provides flags to the subsystem when Broadcast, Mode Code, and Own Address (with parity) commands are decoded. The CT1775 contains a terminal fail-safe timeout circuit which flags message lengths exceeding 768s, and terminates serial data transmission. Wraparound selftest is initiated by a control line which causes the encoder serial output to be connected to the decoder input. The CT1775 provides a serial output of decoded words, thus allowing Command Word look ahead, for the fastest terminal response.