SINGLE CHIP MICROCOMPUTER HAVING UNAUTHORIZED MEMORY SPACE ACCESS PROTECTION

摘要

A single-chip microcomputer connectable to an external memory for expanding the address space, and having a first mode of operation in which the available memory region is both the region of an internal ROM and the external memory, and having a second mode of operation in which the available memory region is the region of the external memory only. An inhibiting device is provided for inhibiting the switching from the second mode to the first mode, thereby ensuring that the contents of the internal ROM cannot be read-out.