Abstract: A distributed multiprocessor communication system, wherein the central processing unit (CPU) is relieved of the burden of bus management by a scheme which multiplexes the interprocessor module communications bus, to which all processors are guaranteed access, so that only an addressed CPU may be interrupted from performing its dedicated data processing function. Associated with each independent processor is a communications interface unit or communications network routing unit which relieves the processor of the task of decoding communications on the interprocessor or intermodule communications bus and, in addition, upon decoding its address and buffering message data, transmits a "handshake" signal over the bus back to the sender during a designated time slot, thereby informing the sender that the transmitted message was actually received.

Abstract: The transmitter of a fire-alarm audible signaling system permitting selective communications and signaling transmits digital command signals to receiver-drivers respectively positioned in a number of fire zones over a single two-wire or three-wire circuit that also provides power to the receiver-drivers. Each command signal includes a frame bit, a zone designator comprising, say, four bits and a function designator comprising, say, three bits. The frame bit is always a one and is always the first bit of the command signal, and it serves as a reference. A comparator in each receiver-driver compares an identification code proper to that receiver-driver with the zone designator of each command signal, and each receiver-driver responds to the function designator of a command signal to perform the designated function only in case of a match between the zone designator of the same command signal and the identification code for that receiver-driver.