A device of this invention solely executes a
power saving operation without influencing a
repeater operation on a serial
bus interface to which a plurality of devices are
cascade-connected.A device such as a
digital camera, printer, or the like, which is
cascade-connected using an IEEE1394 serial
bus interface, uses an IC prepared by forming both physical and link
layers on a
single chip. This IC has a port connected to a
bus. When a power supply on the bus side is OFF, this port can insulate the bus in DC term. This device transits to a
power saving mode such as a
sleep mode, suspend mode, shutdown mode, or the like after an elapse of a predetermined wait time. In the shutdown mode, the
system power supply of the device is turned off, but the IC can operate by
electric power supplied from a cable. With this operation, a
signal can be relayed between devices, and a packet for the
link layer can be received. Upon receiving a LINK_ON packet, the device is restored from the
power saving mode to a normal drive state.