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Figure 6.2. USB desktop connection scheme.
Exam Alert
Memorize the number of devices that can be attached to a USB port.
In this example, some of the peripheral devices are simply devices that perform a
certain function (such as a keyboard), whereas others serve as both devices
(functions) and as connection hubs. These latter devices are referred to as
compound devices. The system provides a USB host connection that serves as
the main USB connection. USB devices can be added to or removed from the
system while it is powered up and fully operational. This is referred to as hot
swapping or hot plugging the device. The plug-and-play capabilities of the
system will detect the presence (or absence) of the device and configure it for
operation.
The USB management software dynamically tracks what devices are attached to
the bus and where they are. This process of identifying and numbering bus
devices is known as bus enumerating. The USB specification promotes hot-swap
peripheral connections that do not require the system to be shut down. The
system automatically detects peripherals and configures the proper driver.
Instead of simply detecting and charting devices at startup in a PnP style, the
USB controller continuously monitors the bus and updates the list whenever a
device is added to or removed from it.
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