| 摘要 |
A power voltage generator is supplied with the power voltage applied directly and via an ignition switch from a battery. The power voltage generator always supplies a power source to a computer equipped with a back-up memory and supplies to a comparator a power voltage signal from the power voltage generator when the ignition switch is turned on. The comparator compares a predetermined voltage signal with the power voltage signal from the power voltage generator. When the power voltage signal is higher than the reference voltage signal, the comparator issues a command to execute the program to a computer. The computer issues a write command to enable the back-up memory when it is judged that the increased voltage is stabilized, to thereby set up a write enable mode. If the power voltage signal drops when the ignition switch is turned off, this condition is detected using the output signal of the comparator. And it is judged whether or not the command to the back-up memory is being executed. If the command is being executed, the write enable state is continued until the command execution ends. The data write to the back-up memory is discontinued when the command execution ends.
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