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The idle line state is when the device is connected to the host with a pull-up on either D+ (for full speed USB 1.x) or D− (for low speed USB 1.x), with transmitter output on both host and device is set to high impedance (hi-Z) (disconnected output). A USB device pulls one of the data lines high with a 1.5 kΩ resistor.
USB communications device class (or USB CDC) is a composite Universal Serial Bus device class. The communications device class is used for computer networking devices akin to a network card , providing an interface for transmitting Ethernet or ATM frames onto some physical media.
USB Battery Charging (BC) defines a charging port, which may be a charging downstream port (CDP), with data, or a dedicated charging port (DCP) without data. Dedicated charging ports can be found on USB power adapters to run attached devices and battery packs. Charging ports on a host with both kinds will be labeled. [52]
A four-port "long cable" "external box" USB hub A four-port "compact design" USB hub: upstream and downstream ports shown. A USB hub is a device that expands a single Universal Serial Bus (USB) port into several so that there are more ports available to connect devices to a host system, similar to a power strip. All devices connected through a ...
Standard USB hub ports can provide from the typical 500 mA/2.5 W of current, only 100 mA from non-hub ports. USB 3.0 and USB On-The-Go supply 1.8 A/9.0 W (for dedicated battery charging, 1.5 A/7.5 W full bandwidth or 900 mA/4.5 W high bandwidth), while FireWire can in theory supply up to 60 watts of power, although 10 to 20 watts is more typical.
In Windows 7 and later, significant hardware changes (e.g. motherboard) may require a re-activation. In Windows 10 and 11, a user can run the Activation Troubleshooter if the user has changed hardware on their device recently. If the hardware has changed again after activation, they must wait 30 days before running the troubleshooter again.
USB 3.0 SuperSpeed – host controller (xHCI) hardware support, no software overhead for out-of-order commands; USB 2.0 High-speed – enables command queuing in USB 2.0 drives; Streams were added to the USB 3.0 SuperSpeed protocol for supporting UAS out-of-order completions USB 3.0 host controller (xHCI) provides hardware support for streams
Windows 8 was the first Microsoft operating system to offer built in support for USB 3.0. [36] In Windows 7 support was not included with the initial release of the operating system. [37] However, drivers that enable support for Windows 7 are available through websites of hardware manufacturers.