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The Universal Serial Bus (USB) is a peripheral bus standard developed by the computer and telecommunications industries. This standard lets you hot plug peripheral devices without restarting or reconfiguring the system. USB devices are automatically configured as soon as they are physically attached. With USB you can connect many peripherals simultaneously. Many computers come with two USB ports. Special USB peripherals, called USB hubs, have additional ports that enable you to connect multiple devices in a daisy chain. USB also distributes electrical power to many peripherals. It enables the computer to automatically sense the power required and deliver it to the device. This feature eliminates those clunky power-supply boxes. USB features include the following:
USB specifications include the following:
5.6.1 USB ConnectorsUSB connectors ship in two distinct varieties, Series A and Series B, as shown in Figure 5-17. Figure 5-17. USB connections.They are identical in function, but have differences to prevent connections that violate the USB architecture topology. 5.6.1.2 SERIES AThe Series A connector has a flat rectangular shape and plugs into the downstream port receptacles on the USB host or hub. Both male connector and female receptacle have all four contact positions inline. The Series A connector is intended for all USB devices. In most cases, a USB cable will be captive (molded in) to its peripheral. 5.6.1.3 SERIES BThe Series B connector, roughly square with beveled corners, plugs into upstream receptacles on a USB device or hub. Both the male connector and female receptacle have four contacts stacked two over two. There are some cases where a captive cable is restrictive. The Series B connector was created for such applications. USB class drivers and Windows Driver Model (WDM), provided in Windows 98 and Windows 2000, support devices that comply with the particular device class specification. Devices can use the generic class drivers provided with the operating system, or manufacturers can create drivers or WDM minidrivers (depending on the device class) to exploit any additional unique hardware features. 5.6.2 USB 2.0USB 2.0 extends the capabilities of the interface from 12Mb/s (200 x 56Kb/s) to between 120 and 240Mb/s. |
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