BUSES AND PROTOCOLS 177
When a USB device is fi rst connected to a USB host, the device ‘enumeration’
process is started. is is a sort of ‘interrogation’ process in which the host asks the device
to give complete information about itself. e enumeration starts by the host sending a
reset signal to the USB device. If the device is supported by the host, the device drivers
needed for communicating with the device are loaded from the operating system of the
host computer and the device is set to a confi gured state. If, say, the host determines
that the device is a ‘standard’ printer, the drivers for this should be available in the host
computer—this is loaded into the USB system and then communication between the
host and peripheral can ...