| 摘要 |
In a microcomputer system arranged to operate with electrical power from a battery installed on a vehicle, the voltage of the power is detected to see whether it is below a predetermined value or not. When the voltage is below the predetermined value, a voltage detector produces an output signal which will be fed to a switching circuit formed by a D-type flip-flop. The D-type flip-flop is also responsive to a read instruction signal applied from the central processing unit of the microcomputer to a nonvolatile random access memory (RAM) thereof which is supplied with power from the battery all the time. With this arrangement, when voltage drop or sag is detected, the RAM is put in stand-by condition in which reading and writing operations are inhibited. In this stand-by condition of the RAM a central processing unit (CPU) of the microcomputer system is capable of operating as long as the power voltage is above the minimum operating voltage of the CPU.
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