A HIGH PERFORMANCE PROCESSOR INTERFACE BETWEEN A SINGLE CHIP PROCESSOR AND OFF CHIP MEMORY MEANS HAVING A DEDICATED AND SHARED BUS STRUCTURE

Methods and apparatus for realizing a high performance interface between a processor, constituting part of a reduced instruction set computer (RISC) system, and a set of devices, including memory means. According to the invention, the interface includes three independent buses. A shared processor output bus, a processor input instruction bus, and a bidirectional data bus. The shared processor output address bus coupled the processor and the computer's memory. This bus carries both instructon and data access signals being transmitted by the processor to the memory. The processor input instruction bus also couples the processor and the computer's memory means, but carries instruction signals being transmitted from the memory to the processor. The bidirectional data bus provides a signal path for carrying data signals being transmitted by the memory to the processor and vice-a-versa. The novel interface uses demultiplexed buses for simpler timing and uses the separate data and instruction buses to provide extremely high transfer rates at a reasonable cost. The shared address bus accommodates pipelined and burst mode processor protocols with the burst mode protocol allowing concurrent data and instruction transfers. Methods and apparatus for controlling the buses and reporting bus status, etc., are also part of the invention and facilitate the implementation of features that include status reporting, handshaking between devices and the RISC processor, and bus arbitration.