The invention provides a method for Serial-Peripheral-Interface (SPI) data transmission. First, data stored in a first buffer of an SPI controller is transmitted to a second buffer of an SPI slave. A clock signal according to which the SPI slave operates is halted after data stored in the first buffer is completely transmitted. The first buffer is then refreshed with data newly received by the SPI controller while the clock signal is halted. The clock signal is then restarted to operate the SPI slave after the first buffer is refreshed. Refreshed data stored in the first buffer is then transmitted to the second buffer while the clock signal is oscillating. Halting of the clock signal, refreshing of the first buffer, restarting of the clock signal, and transmitting of refreshed data are repeated until the second buffer is full. The buffer size of the second buffer greatly exceeds that of the first buffer.