US Patent 7149127 Flash memory card

A flash memory card comprises a flash memory and a controller. The flash memory stores data. The controller detects frequency variation of an external clock signal inputted from a host to generate an internal clock signal. The controller controls the flash memory in response to the internal clock signal. The controller includes a clock-frequency control unit and a clock generator. The clock-frequency control unit detects frequency variation of the external clock signal to generate a detection signal. The clock generator receives the detection signal to generate the internal clock signal. A frequency of the internal clock signal varies corresponding to the frequency variation of the external clock signal.