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U
USB or Universal Serial Bus
A smart plug for PC peripherals. USB automatically determines resources (like driver software and bus
bandwidth) required by peripherals. USB makes necessary resources available without user intervention.
● USB eliminates "case angst" -- the fear of removing the computer case to install add-on peripherals.
And USB also eliminates adjustment of complicated IRQ settings when installing new peripherals.
● USB does away with "port gridlock." Without USB, PCs are normally limited to one printer, two Com
port devices (usually a mouse and modem), one Enhanced Parallel Port add-on (scanner or video
camera, for example) and a joystick. More and more peripherals for multimedia computers arrive on
the market every day. With USB, up to 127 devices can run simultaneously on a computer.
● USB permits "hot plug-in." There's no need to shut down, plug in, reboot and run set-up to install
peripherals. And no need to go through the reverse process to unplug a device.
In short, USB transforms today's "Plug-and-Pray" into true Plug-and-Play!
Hub
A Universal Serial Bus device that provides additional connections to the Universal Serial Bus.
Hubs are a key element in the plug-and-play architecture of USB. The Figure shows a typical hub. Hubs
serve to simplify USB connectivity from the user's perspective and provide robustness at low cost and
complexity.
Hubs are wiring concentrators and enable the multiple attachment characteristics of USB. Attachment points
are referred to as ports. Each hub converts a single attachment point into multiple attachment points. The
architecture supports concatenation of multiple hubs.
The upstream port of a hub connects the hub towards the host. Each of the other downstream ports of a
hub allows connection to another hub or function. Hubs can detect, attach and detach at each downstream
port and enable the distribution of power to downstream devices. Each downstream port can be individually
enabled and configured at either full or low speed. The hub isolates low speed ports from full speed
signaling.
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