Patent ID: 6973522

Claim:
A microcomputer including a read-only memory that stores programs, a controller/calculator that successively accesses addresses of the programs stored in said read-only memory to retrieve and decode an instruction from the accessed addresses, to execute a process based on the decoded instruction, and a program counter in which an address to be accessed by the controller/calculator is successively renewed, said microcomputer comprising: at least one comparison-address-storage device that stores comparison address data corresponding to an optional address of the programs stored in the read-only memory, at which an interruption-process is executed to virtually revise the programs stored in the read-only memory by adding a program; a random-access memory that stores a revisional program in which the interruption-process is programmed; at least one vector-address-storage device that stores vector address data corresponding to a head address of the revisional program stored in said random-access memory; an address comparator that compares the comparison address data with an address successively renewed in the program counter; wherein the controller/calculator accesses the head address of the revisional program, stored in said random-access memory, corresponding to the vector address data stored in said vector-address-storage device, when there is a coincidence between the comparison address data and the renewed address of the program counter, resulting in an execution of the interruption-process in accordance with the revisional program; a return-address-setter that sets return-address data in the program counter to coincide with the comparison address data when execution of the interruption-process in accordance with the revisional program is completed; and an address-coincidence-disabler that disables the coincidence between the comparison address data and the return-address set in the program counter by said return-address-setter in response to a control flag that is set in the revisional program.