A method of a flash memory controller includes: providing an input/output (I/O) circuit coupled to the flash memory device; and sending a data toggle set-feature signal to the flash memory device to enable, disable, or configure a data toggle operation of the flash memory device; the data toggle operation of the flash memory device is arranged to make the flash memory device control the flash memory device's data register selecting and transferring a first data unit and a second data unit to the flash memory device's I/O control circuit to make the I/O control circuit sequentially transmit the first data unit and the second data unit to the flash memory controller through the specific communication interface in response to a specific read command or a data toggle command transmitted by the flash memory controller.