Data General Corporation

Karsten Sorensen

David H Bernstein

Michael B Druke

A data processing system in which the central processor unit operates asynchronously with one or more memory units independently of the operating speed of the memory units wherein the central processor timing signal and the memory timing signal have a predetermined phase relationship. The central processor unit is arranged to remain operative even when the memory unit is enabled unless it is disabled by a signal from the memory unit under preselected conditions. The central processor generates a plurality of operating instruction signals for transfer to the memory unit to permit the latter to perform its desired functions by enabling the memory unit, inhibiting the transfer of data from the memory unit to a data bus and permitting storage of data from the central processor unit when data is acceptable for such storage. A further operating instruction signal is generated at the central processor unit to permit data read from the memory unit to be modified at the central processor unit and stored in the memory unit after such modification. A further operating instruction signal is generated internally to the memory unit to prevent operation of all other memory devices in the memory unit when one of the memory devices therein is in operation. The logic for providing operation in a program or a non-program operating state is arranged to utilize one or more relatively small read-only-memory units for each of a plurality of selected groups of program and non-program operating states, each group using only one or two of such read-only-memory units for such purpose. The central processor unit further includes a unique arrangement interconnecting a skew protected, tri-state register file having two read and two write ports with an arithmetic logic unit having an output and an A-input and a B-input.

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Lexington, MA, United States of America

Karsten Sorensen