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USB Explained by Martin D. Seyer, Steven McDowell

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Chapter 6On the Wire

The USB Protocol

It is all well and good to string USB devices and hosts and hubs together, but without a coherent communication scheme they aren’t really much good. Fortunately, the designers of the Universal Serial Bus understood this fundamental limitation and gave us the Universal Serial Bus protocol.

The USB protocol allows the devices to all talk to and understand each other. It defines how a device should interpret a stream of bits flowing down the wire. Where does a frame start and end? What kind of data are we looking at? All of these questions, and many more, are answered for the device if it understands the USB bus protocol. We’ll talk about the USB protocol in depth in this chapter.

We’re going to look at things ...

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