DATA PROCESSING UNIT

摘要

PURPOSE:To secure a data in an EPROM by devising such that a data in the EPROM is not read through the use of a bus extension mode in a single chip microcomputer incorporating the Erasable Programmable ROM (EPROM) and having a bus extension mode. CONSTITUTION:A protect bit 8 comprising a nonvolatile storage element to set whether or not a data in the EPROM 11 is to be secured is provided in a single chip microcomputer incorporating the EPROM 1 and having the bus expansion mode. Then the information of the protect bit 8 is given to a mode control circuit 9 forming a control signal operating the inside of the single chip microcomputer at the set mode and when a write is applied to the protect bit 8, the bus expansion mode of the single pitch microcomputer is inhibited. Since the bus expansion mode itself is inhibited, the data secrecy in the EPROM is protected.