Bus system for coordinating internal and external direct memory access controllers

A microprocessor system comprising:

• a main processing unit including an instruction execution unit, having a logical address register for storing a logical address to be accessed, and a DMA controller having a DMA register for storing an address for direct memory access;
• hit determining means for determining whether an address hits data stored in an external cache memory;
• an address array controller responsive to the results from said hit determining means for accessing an external address array connected to the cache memory, to control passage of address signals to the cache memory;
• an address bus and a data bus, each said bus connected to said main processing unit and adapted for connection to an external DMA controller;
• means within said hit determining means for comparing an address of said DMA register or of the external DMA controller with address signals from said address array;
• invalidating means responsive to the comparison by said comparing means for invalidating the cache memory address by applying an invalid bit on said bidirectional address array to write the invalid bit at the cache memory address;
• said main processing unit, said hit determining means, said address array controller, and said invalidating means being formed on a single chip as a one-chip microprocessor;
• a memory controller adapted for connection to a main memory;
• a multiplexed address/data bus coupling said main processing unit and said memory controller and adapted for connection to the cache memory;
• an address latch coupling said address bus with said multiplexed address/data bus;
• a driver coupling said data bus with said multiplexed address/data bus;
• and
• by-pass means for passing an address from said address bus to said main processing unit;
• and wherein:
• said invalidating means is responsive to address information from said main processing unit DMA controller and the external DMA controller for invalidating a cache memory address;
• whereby:
• address information and data can be transferred by said multiplexed address/data bus between said main processing unit and said memory controller to permit accessing of the main memory;
• address information and data can be transferred by said multiplexed address/data bus and said bus means between said main processing unit and said external DMA controller;
• address information can be applied from said main processing unit DMA controller through said multiplexed address/data bus and said memory controller to the main memory to cause data to be transferred from the main memory through said memory controller onto said data bus;
• and
• address information can be applied from the external DMA controller through said address bus, said by-pass means, said multiplexed address/data bus and said memory controller to the main memory to cause data to be transferred from the main memory through said memory controller onto said data bus, and the address information applied from the external DMA controller through said address bus can be transferred to said hit determining means for comparison with data from the external address array, for invalidating said cache memory in accordance with the result of the comparison.