A master device communicates with a slave device through an asynchronous serial communications link. The master device includes a single pad configured to communicate a command frame including an address and a data frame including data with the slave device via a single wire; and a processing circuit configured to generate an oversampling clock signal from a clock signal, to perform a synchronization process for selecting one of a plurality of clock phases of the oversampling clock signal, and to perform a sampling process for sampling an each bit value included in the data frame transmitted from the slave device using a clock phase at the same position as the clock phase selected during the synchronization process.