Hardware Reference
In-Depth Information
Figure 2.10
A modern PC with motherboard USB ports and host controller
circuitry
•
Allows a wide range of device data rates
•
Flow control for buffer handling is built into the protocol
•
Robust (incorporates error detection and fault recovery mechanisms)
•
Relatively low-cost.
USB implementation
Most current desktop and tower PCs as well as Apple iMac computers are
supplied with one or more USB ports. On PCs, these ports are additional to
those that are normally associated with the original PC standard, such as the
two serial ports (COM1: and COM2:) and the parallel port (LPT1:).
On most current PCs, the USB ports are functions provided by the system
motherboard (see Figure 2.10). Older PCs can easily be fitted with USB ports
by simply adding a low-cost adapter card (see Figure 2.11). However, in either
case, the operating system must support the USB standard. This means that PC
owners will have to upgrade to Windows 98 or later in order to have a system
that
fully
implements the USB standard!
