TAILIEUCHUNG - USB Complete fourth- P41

USB Complete fourth- P41:This book focuses on Windows programming for PCs, but other computers and operating systems also have USB support, including Linux and Apple Computer’s Macintosh. Some real-time kernels also support USB. | Chapter 15 tion translators and routing logic that enable low- and full-speed devices to communicate on a high-speed bus. The host s root hub is a special case. The host controller performs many of the functions that the hub repeater and hub controller perform in an external hub so a root hub may contain little more than routing logic and downstream ports. The Hub Repeater The hub repeater re-transmits the packets it receives sending them on their way up or down stream with minimal changes. The hub repeater also detects when a device is attached and removed establishes the connection of a device to the bus detects bus faults such as over-current conditions and manages power to the device. A USB hub repeater has two modes of operation depending on the upstream bus speed. When the hub connects upstream to a full-speed bus segment the repeater functions as a low- and full-speed repeater. When the hub connects upstream to a high-speed bus segment the repeater functions as a high-speed repeater. The repeaters in USB hubs always function as low- and full-speed repeaters. The Low- and Full-speed Repeater The hub repeater in a USB hub handles low- and full-speed traffic. A USB hub also uses this type of repeater when its upstream port connects to a full-speed bus. In this case the USB hub doesn t send or receive high-speed traffic but instead functions identically to a USB hub. A low- and full-speed repeater re-transmits all low- and full-speed packets received from the host including data that has passed through one or more additional hubs to all enabled full-speed downstream ports. Enabled ports include all ports with attached devices that are ready to receive communications from the hub. Devices with ports that aren t enabled include devices that the host controller has stopped communicating with due to errors or other problems devices in the Suspend state and devices that aren t yet ready to communicate because they have just been attached or .

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• sửa chữa máy tính
• sổ tay phần cứng
• MainBoard
• thiết bị máy tính
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• lắp ráp máy tính
• Phần cứng máy tính
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