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The hub built into the host controller is called the root hub. A USB device may consist of several logical sub-devices that are referred to as device functions. A composite device may provide several functions, for example, a webcam (video device function) with a built-in microphone (audio device function).
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 ...
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.
For example, a USB 2 PCIe host controller card that presents 4 USB "Standard A" connectors typically presents one 4-port EHCI and two 2-port OHCI controllers to system software. When a high-speed USB device is attached to any of the 4 connectors, the device is managed through one of the 4 root hub ports of the EHCI controller.
Full-featured USB-C 3.1 cables contain a full set of wires and are "electronically marked" : they contain a "eMarker" chip that responds to the USB Power Delivery Discover Identity command, a kind of vendor-defined message (VDM) sent over the configuration data channel (CC). Using this command, the cable reports its current capacities, maximum ...
In USB 3.0, dual-bus architecture is used to allow both USB 2.0 (Full Speed, Low Speed, or High Speed) and USB 3.0 (SuperSpeed) operations to take place simultaneously, thus providing backward compatibility. The structural topology is the same, consisting of a tiered star topology with a root hub at level 0 and hubs at lower levels to provide ...
Printable version; In other projects ... USB may also refer to: Science and technology ... USB hub; Wireless USB; USB flash drive;
A USB compound device contains an embedded USB hub and one or more non-removable USB devices. [1] It may or may not have exposed downstream ports. The internal USB hub may be a physical IC that connects to other ICs, or the hub and all functions may be implemented in software on a single IC (though it is more common to integrate them as a composite device in this case).