Patent ID: 7149906

Claim:
A communication device for transmitting/receiving data to/from a host device connected thereto via a bus having a signal line and a power line, comprising: communication control means for responding to communication from the host device, the communication control means being supplied with power while the bus is connected thereto; communication function means for controlling data transmission/reception with the host device through the communication control means, the communication function means working under power supplied via the bus, wherein said communication function means comprises a Memory Control Unit (MCU); and power supply control means for controlling supply of power to the communication function means based on the state of the host device notified from the communication control means; wherein, when the host device transits into stand-by state, the power supply control means interrupts supply of power to the communication function means, and when communication control means detects a resumed active state of the host device, the power supply control means resupplies power to the communication function means, and wherein the communication control means notifies the host device of a ready status of the communication function means.