Abstract: In a multiple-board computer system, diagnostics are primarily performed by highly reliable microcontroller units (MCUs) on each processor (and memory) board. Operated separately from the board central processing units so that board failure will not prohibit diagnostic routines, the MCUs are serially connected to a bus separate from the main bus. Redundant diagnostic processor board MCUs constantly monitor the other MCUs and the serial bus, and oversee the operation of an MCUs on a malfunctioning board. In an alternate embodiment the diagnostic processor boards are replaced by a microcomputer serving as a monitor.

Abstract: A data processing system has a plurality of subsystems or terminals, each containing an independent processor, the terminals linked by a star coupler. The system includes a star coupler to which all the terminals are connected over sending and receiving transmission lines. The function of the coupler is to take the signals received by the coupler, logically ORing all these received signals, and redriving the resulting signal to all processors via the receive side transmission line. To prevent one terminal or processor from tying up the coupler for an undue length of time, the coupler includes means for detecting a message length exceeding a predefined maximum, and determines this to be an overrun condition. When the overrun occurs, the channel from the offending terminal or processor is blocked by the coupler from reaching the logical ORing functional center of the coupler. In this way, the linking section of the star coupler remains as an operative link among the remainder of the processors.

Abstract: A retail store having a computer, point-of-sale terminals, and product code readers at the point-of-sale terminals, includes an electronic price display system. The display system has plural display units, with one display unit at each of the locations in the store where items are held for sale. The computer controls both the prices which are displayed by the display units and the prices which are charged to customers at the point-of-sale terminals. The display units are connected in electrical series by a data transmission line, and price information is transmitted by the computer over the transmission line to the display system in the same order as the display units are connected.