A method for transferring data between a serial peripheral interface (SPI) master device and an SPI slave device generates a first clock signal for the SPI master device and a second clock signal for the SPI slave device. Clock frequency of the first clock signal and the second clock signal is twice than a serial clock signal between the SPI master device and the SPI slave device. Data are transferred with double data rate or single data rate based on the first clock signal and the second clock signal.