Hardware Reference
In-Depth Information
Figure 2.11
A PC with adapter card USB ports and host controller circuitry
The USB circuitry on the motherboard (or the adapter card) provides the
functions of a USB host controller. This circuitry, in conjunction with buffers
and drivers, provide the basic host interface to the USB.
Connection and disconnection of USB devices
One of the advantages of USB over other bus systems is its ability to support hot-
connection and hot-disconnection from the bus. This important feature requires
that the host's system software is not only able to recognize the connection and
disconnection of devices but is able to reconfigure the system dynamically.
Modern operating systems, such as Microsoft Windows 98, 2000 and XP have
this facility.
USB devices attach to the USB through ports on hubs that incorporate status
indicators to indicate the attachment or removal of a USB device. The host
queries the hub to retrieve these indicators. In the case of an attachment, the
