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USB Explained by Martin D. Seyer, Steven McDowell

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Chapter 5Inside a USB Device

What Does a USB Device Do?

The first thing that you should understand about a Universal Serial Bus device is that nearly everything within a USB system is a device. The root hub is a device, as is every hub connected to the system. The peripherals that you attach to the Universal Serial Bus are all known as devices. The only part of a system that isn’t a USB device is the actual host controller (and the controlling system software).

Each USB device is divided into three distinct and individual layers. The bottommost layer is the part of the device that is responsible for communicating on the physical bus by sending and receiving packets. The next layer up is the protocol engine that is responsible for translating ...

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