MICROCOMPUTER INCORPORATING EEPROM

摘要

PURPOSE:To keep the content of an EEPROM (Electrically Erasable & Programmable ROM) without destroying even when the runaway or malfunction of a CPU occurs by providing an area designation means to designate a write permission area and a write prohibition area. CONSTITUTION:A write permission area designation register 8-a designates an area to permit write and an area to prohibit the write actually out of all areas of the EEPROM 3 when a write instruction is executed. An area discrimination circuit 10 outputs a write prohibition signal to a read/write control circuit 11 when an address area shown by an identification signal from an address decoder 9 coincides with the address area designated to write prohibition by the output of the write permission area designation register 8-a. Thereby, by generating a program so as to be set on the write permission area designation register 8-a so that write prohibition can be set on a prescribed data storage area, the content of the EEPROM can be held without being destroyed even when the runaway or malfunction of the CPU occurs.