Data storage device and control method for power-saving modes of serial interface thereof

Embodiments of the invention reduce consumption power of a data storage device. In one embodiment, an HDD according to the embodiment selectively switches a serial interface among other circuits to a power-save mode. The HDD receives a command from a host, and, in a command execution sequence thereof, sets and keeps the serial interface in the power-save mode for at least a partial period of time during which no sending and receiving of data resulting from serial data communication with the host exists. Further, in responding to completion of execution of the command, the HDD switches the serial interface to the power-save mode.