| 摘要 |
PURPOSE:To protect the memory state of a RAM by inhibiting an access to the backup RAM when a power source voltage drops below the 1st prescribed voltage and resetting a CPU when it drops below the 2nd lower prescribed voltage. CONSTITUTION:A microcomputer 11 including the CPU 12, etc., processes an input signal from an input signal processing circuit 18, and outputs it through an output signal drive circuit 19. Its power source circuit 17 includes a voltage drop detecting circuit 172 and a backup power source 173 as well as a constant voltage circuit 171. When the voltage drop detecting circuit 172 detects that the power source voltage drops below the 1st prescribed value, it applies a nonmaskable interruption to the CPU 12, which inhibits the access to the backup RAM 15. When the power source voltage drops below the 2nd lower prescribed value, the CPU 12 is reset and its action is stopped.
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