| 摘要 |
PURPOSE:To efficiently back up a memory by impressing power supply voltage more than the operation voltage of a memory IC to the memory ID at the time of impressing the power supply voltage from the external, and at the time of back-up operation, allowing current to flow from a battery only into the memory IC. CONSTITUTION:A power supply voltage control circuit 4 is connected between an I/O terminal and the memory IC 1 and a capacitor C and a memory back-up battery B are connected between the memory IC 1 and the circuit 4. Only when a voltage >= the operating voltage of the memory IC, the circuits 4 generates output voltages for two systems, one output is connected to the capacitor C and the other is connected to the battery B and the memory IC 1 through a diode D. When the power supply voltage is impressed from the external, a voltage almost equal to the voltage impressed from the external is impressed to the memory IC 1, and at the time of back-up operation, current flows from the battery B only to the memory IC 1 and the memory can be efficiently backed up. |
