Abstract: A memory card circuit for a portable memory card includes a unidirectional non-inverting buffer with an analog switch connected to an input terminal of a semiconductor memory and a bidirectional 3-state buffer with an analog switch connected to an input/output terminal of the memory card. An analog switch connected is series to a terminal signal of the semiconductor memory and a second analog switch connected in parallel to ground in parallel interfaces the card to a terminal unit. A transistor connected in series between a power supply input from the terminal unit and an internal power supply of the memory card, a supply voltage detecting circuit having inputs of a card insertion and extraction signal and a supply voltage of the memory card produces an output signal for turning ON or OFF the series transistor, the unidirectional non-inverting buffer with the analog switch and the bidirectional 3-state buffer with the analog switch.