Term Definition
Downstream Thedirectionof data flow f romthe host or away from the host. A
downstreamport is the port on a hubelectrically f arthestf romthe host t hat
generatesdownstreamdata traffic f romthe hub. Downstream interfaces
receiveupstream data traffic.
Full-speed USB operationat 12 Mbps
Function A USB device that provides a capability to the host, such as a keyboard,
interactivewhiteboard or speakers.
High-speed USBoperationat 480 Mbps
Host Thehost computersyst emwhere the USB hostc ontrolleris installed. This
includesthe host hardware platform(CPU, bus, etc.) and the operating
system in use.
Host controller Thehost’s U SB interface hardwareands oftware
Hub A USB device that provides additionalconnections to the bus
Low-speed USB operationat 1.5 Mbps
Passive
(extensioncable)
An extensioncable that has no active electronic components. For more
information,see Prohibitedc ableassemblies on page20.
Physical device A device that has a physical implementation;f orexample, speakers,
microphones,and CD players.
Port A USB hub’s downstreamconnection point wherea USB device is
attached
Root hub AU SB hub directly attachedt o thehost controller
Upstream Thedirection of data flow toward the host. An upstream connectoron a
deviceis electrically closest t o the host that generatesupstream datatraffic
fromthe hub. Upstream interfaces receive downstreamdata traffic.
AP P E N DI X A
USB2.0 specification primer
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