USB Physical layer and components description

USB Physical layer and components description

USB 1.0 Low speed –  1.5Mbps

USB 1.1 Full Speed  –   12 Mbps

USB 2.0 – High Speed  – 480 Mbps

USB 3.0Supper Speed3.2 Gbps

Bus Topology


Refer. Sec 4.1.1 – USB 2.0 spec

Due to timing constraints allowed for hub and cable propagation times, the maximum number of tiers allowed is seven (including the root tier). Note that in seven tiers[above fig. shows only 4] , five non-root hubs maximum can be supported in a communication path between the host and any device.

USB Host – There is only one host in any USB system. The USB interface to the host computer system is referred to as
the Host Controller. A root hub is integrated within the host system to provide one or more attachment points.

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USB Devices – USB devices are one of the following

• Hubs – which provide additional attachment points to the USB
• Functions – which provide capabilities to the system. such as, pen drive, usb keyboard, mouse


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