Serial Interface Transmitting method and Peripheral Device Chip

The present invention discloses a serial interface transmitting method utilized in a serial interface for connecting between a master controller and a peripheral device. The serial interface transmitting method comprises receiving a saving power signal from the master controller, a peripheral clock source and a serial interface clock source for generating a clock source selection result, switching an operational mode of the peripheral device according to the clock source selection result, and transmitting a datum to a peripheral-device register or a serial interface register according to the saving power signal and the operational mode.