Information Technology Reference
In-Depth Information
Figure 2-1: USB cable plugs from left to right: series-A, series B, mini-A, and
mini-B.
Detect Devices
On power-up, hubs make the host aware of all attached USB devices. In a
process called enumeration, the host assigns an address and requests a series
of data structures called descriptors from each device. After power-up,
whenever a device is removed or attached, the host learns of the event and
enumerates any newly attached device or removes any detached device from
the record of available devices.
Provide Power
The host provides power to all devices on power-up or attachment and
works with the devices to conserve power when possible. Some devices draw
all of the power they need from the bus, while others have their own power
supplies to supplement or replace the bus power.
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