Method of producing microaddresses and a computer system for achieving the method

摘要

A central processing unit of a computer system comprises a programmable logic array which is constructed of an AND matrix and an OR matrix. The AND matrix is responsive to a machine language instruction and to a number of a region for selecting one row from a plurality of rows arranged in the AND matrix. The OR matrix, which also has a plurality of rows, is responsive to the selected row for selecting one row therefrom. In each of the rows of the OR matrix a microaddress and a number of a region to be used for producing a subsequent microaddress are prewritten so that information on a microaddress and information on a region number are respectively obtained. At least one microinstruction included in a microprogram will be read out from a read-only memory in accordance with the obtained microaddress to execute the same, while a microaddress of a subsequent microprogram is produced in the programmable logic array. Namely the execution of a microprogram routine and the production of the first address of a following microprogram routine are concurrently performed so that efficient execution of microprograms can be achieved, while each microinstruction is not required to include region number information.