| 摘要 |
PURPOSE:To secure the data of a RAM so that proper data can be communicated by connecting the first terminal to a terminal, through which a power supply voltage is supplied to a whole system, and one ends of the first and third resistances. CONSTITUTION:When a power supply voltage drops, the voltage is inputted to a minus side after the voltage is resistively divided. Since the input value on the minus side becomes lower than the voltage on the plus side which is used as a reference voltage, the output of a comparator 106 is inverted and becomes high in level. When the output of the comparator 106 becomes a high level, a P-channel and N-channel MOS transistors 108 and 107 turn off. The electric charges accumulated in a capacitor 105 are supplied to the power supply terminal of a RAM 101 as backup power supply. In addition, since an MPU 102 stops operation and a constant-voltage detection circuit 104 detects the drop in the power supply voltage and inputs an access inhibiting signal against a CS terminal, the RAM 101 only operates to hold data. |
