A mobile device includes a slave device that receives first data provided to a serial data line in synchronization with a clock signal provided through a serial clock line, and outputs second data to the serial data line in synchronization with the clock signal; and a master device that generates the clock signal and provides the first data to the serial data line in synchronization with the generated clock signal, or receives the second data output to the serial data line in synchronization with the clock signal. The master device generates the clock signal of a first frequency upon transmitting the first data, and generates the clock signal of a second frequency, which is lower than the first frequency, upon receiving the second data.