| 摘要 |
PURPOSE:To maintain the secrecy of the data contents of an internal ROM or internal E<2>PROM by preventing an operation mode in program execution from being changed into an internal ROM operation mode. CONSTITUTION:This microcomputer is equipped with at least an address decision circuit 2, an internal ROM 3, a selector 4, a CPU 5, and a latch circuit 6 corresponding to an external memory 7, and the data input from an operation mode specification terminal 51 and the output signal of a latch circuit 6 generated by the reset signal input from a reset terminal 52 are inputted to the address decision circuit 2. Consequently, the logical value at the operation mode specification terminal 41 at the time of reset mode releasing is held and the logical value at the operation mode specification terminal 51 at the time of a change from a reset level to a non-reset level is latched. The output of the latch circuit 6 does not vary. Therefore, the operation mode in program execution is never changed into the internal ROM operation mode at the start of operation in external memory operation moded. |
