Patent ID: 6588010
Filing Date: 2003-07-01
Classification: G06F

Abstract:
A computer system comprising a microcomputer and external memory means in communication with the microcomputer for storing various programs and various items of data, the microcomputer comprising a nonerasable ROM having stored therein a basic program and basic data for controlling the operation of the computer system, a RAM for storing various programs or various kinds of data, a CPU for executing programs and processing data, and an interface circuit for providing communications with external devices, the computer system being characterized in that:the external memory means has stored therein a modification program serving as program data for modifying a portion of program data contained in the basic program, a modification starting address indicating a location in the basic program where the modification of the basic program by the modification program is to be started, and a code offset indicating the code length of the modification program, the CPU having an address interrupt function for processing an interrupt at a predetermined interrupt address, the microcomputer comprising read means for reading the modification program and the modification starting address from the external memory means, transferring the modification program and the code offset to the RAM and storing the modification starting address in the CPU as the interrupt address, and means for making reference to the code offset, specifying a head address of the modification program in the RAM, and executing a command to jump to the head address for an address interrupt, wherein the external memory means has stored therein modified data for modifying the basic data, and the microcomputer comprises means for transferring the basic data from the ROM to a predetermined location in the RAM, and substitution means for reading the modified data from the external memory means and transferring the modified data to the predetermined location in the RAM to substitute the modified data for the basic data.