| 摘要 |
PURPOSE:To realize a securer fail-safe by adding a simple hardware such as a writing permitting flag, a reading permitting flag, an address decoder to a secret zone in a PROM memory and a timer for detecting a runaway to a P(Programmable)ROM block. CONSTITUTION:The microcomputer has an address decoder, a writing permitting flag 154, a reading permitting flag 153, a timer 152 for detecting a runaway, a gate circuit to output a read strobe signal to a PROM only when a reading permitting flag 153 goes to a reading permission, a gate circuit to output a write strobe signal 1519 to a PROM 11 only when a writing permitting flag goes to a writing permission, and a gate circuit to output an access error signal 1516 and execute the interruption processing request to a CPU when a zone selecting signal 1510 is outputted and both a read strobe signal 1520 and a write strobe signal 1519 are not outputted, and executes the access processing to a secret zone. Thus, the unjust data access to occur by a software processing is prohibited and a security is increased. |
