1. A method of implementing a power down in a memory device capable of performing a read operation in which outputs of the memory device include data and a data strobe signal that oscillates between first and second states during the read operation in accordance with a timing of the data, the method comprising: generating a first signal for preventing the data from being supplied as an output of the memory device; generating a second signal for causing the data strobe signal to remain in a predetermined state; and generating a third signal for preventing the data strobe signal in the predetermined state from being supplied as an output of the memory device.