| 摘要 |
PURPOSE:To prevent the generation of malfunction of a CPU due to data for losing reliability by deciding the effectiveness an invalidity of contents of a memory device based on contents of a battery level detecting memory circuit at power restoration. CONSTITUTION:When a power supply switch 3 is in the off-state, an electric power source is supplied to the memory device 2 from a backup battery 4, and contents in the memory are protected. The battery level detecting memory circuit 9 monitors the level drop of the backup battery 4. When the voltage of the battery 4 drops to a value close to the value which hardly protects the memory device 2, the circuit 9 holds the drop to store it. An initial program at the point when the power supply switch 3 is turned on and the CPU1 starts its action reads the contents in the battery level detecting memory circuit 9, which are used for deciding whether or not contents in the memory device 2 are damaged, and the necessity of charging the battery 4 or its exchange is reported to an operator. |
