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USB System Architecture (USB 2.0).pdf
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Chapter 2: The Big Picture

High-Speed Devices in a 2.0 System

High-speed devices like lowand full-speed devices may also be attached to any 2.0 host controller port or 2.0 hub operating at high speed. Figure 2-13 illustrates a collection of high-speed devices attached to high-speed ports. Transactions generated by a high-speed (HS) host controller are repeated to all HS devices, while these transactions are blocked from reaching fulland low-speed devices.

Figure 2-13: Example of High-Speed Devices Attached to 2.0 Root Hub and High-Speed Hub

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High-Speed Devices Attached to 1.x Ports

High-speed devices that connect to full-speed ports must operate correctly at full speed. Note that even though the device must operate at full speed it may be limited to supporting only accesses via endpoint zero (e.g., reading its descriptors). Thus, a HS device is not required to have full functionality at full speed.

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