A portable electronic device including a USB connector, an internal power source,
a USB controller to execute data communication processing for data communication
with a personal computer connected to the USB connector, a main CPU to execute
device operation processing for usual operation of the device. When the USB controller
executes data communication processing, the device is supplied with power at high
voltage from the personal computer through the USB connector. When the main CPU
executes device operation processing, the device is supplied with power at low
voltage from the internal power source. Accordingly, this makes not only high speed
data communication available, but also prolongs the life of the internal power source.
