A two-wire interface (300) for connecting a first device (106) and a second device (108). The two-wire interface (300) is operable in a handshaking mode and a data transfer mode. In the handshaking mode the first wire (302) of the interface (300) is driven by the first device (106) and the second wire (304) of the interface (300) is driven by the second device (108) so that the first (106) and second (108) devices can perform a handshaking sequence. In the data transfer mode one of the first wire (302) and the second wire (304) is driven by one of the first (106) and second (108) devices to provide a clock signal, and the other wire is driven by either the first device (106) or the second device (108) depending which device is transmitting data. Accordingly, the two-wire interfaces (300) are operable in two modes (e.g. handshaking mode and data transfer mode) and one of the wires (302, 304) of the interface (300) may be driven by a different device in the two modes.