Abstract: A stored data protection apparatus for an electronic device has a CPU (20) and a volatile memory (21) controlled by the CPU for storing data therein. Both of the CPU and the volatile memory ace supplied power voltage from a main battery (22) in normal operation of the device. The volatile memory as supplied power voltage from a back-up battery (23) when the main battery is removed from the device. The apparatus has a switch (29) operable in first and second positions, taking the first position in the normal operation of the device, and being switched from the first position to the second position when the main battery is removed from the device, a circuit (44, 48) for inhibiting the CPU to access the volatile memory when the switch is in the second position, and a circuit (38, 34, 42, 43) for releasing the inhibition of the CPU by the inhibiting circuit when the switch is switched from the second position to the first position.

Abstract: An electronic apparatus is provided with a main battery, semiconductor memories having a chip select input (active low), a backup battery, a pull-up resistor, a control unit for selecting one of the semiconductor memories, and a selection control line connected between the control unit and the chip select input. The selection control line is connected to the backup battery through the pull-up resistor. A switch for closing or opening the selection control line is connected between the selection control unit and the junction point of the control line and the pull-up resistor. A switch control unit is provided which controls the switch to open the control line when the semiconductor memory is powered by the backup battery. In another electronic apparatus having a detection circuit for detecting the voltage of the backup battery, the switch is closed only when the voltage is to be monitored.

Abstract: A capacitive type coupling data transmission system for portable electronic apparatus is comprised of an input circuit, a capacitance changing circuit, a transmitting circuit capacitively coupled to, a receiving circuit, and a detecting circuit for detecting any change in the capacitance changing circuit. A data signal to be transmitted is inputted into the input circuit. Based on the value of an inputted binary digital data signal, the capacitance of the capacitance changing circuit is changed. The capacitance change is capacitively transmitted from the transmitting circuit to the receiving circuit and detected thereat. The detecting circuit may be an oscillator circuit, a an RC differentiating circuit, or an RC integrating circuit.