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USB Tutorial

(Information compiled from internal and external sources. Wikipedia.org, etc.)

What is USB?

Short for Universal Serial Bus, an external bus standard that supports data transfer rates of 12 Mbps. A single USB port can be used to connect up to 127 peripheral devices, such as mice, modems, and keyboards. USB also supports Plug-and-Play installation and hot plugging.

What is USB 2.0?

Also referred to as Hi-Speed USB, USB 2.0 is an external bus that supports data rates up to 480Mbps. USB 2.0 is an extension of USB 1.1. USB 2.0 is fully compatible with USB 1.1 and uses the same cables and connectors.

What are USB Type A or B Male and Female Connectors?

USB A Male
USB A Female
Type A - Type A are Upstream connectors toward Host computer.

USB B Male
USB B Female
Type B - Type B are Downstream connectors toward Devices.

The USB connectors & cables carry power, ground and a differential pair of data lines. USB connectors are designed so you can only make proper connections between the USB Host and USB (slave) Devices. Two USB devices can only communicate with the Host, not directly with each other

USB cables have a distance limitation of 17.5 Feet.

USB Topologies and Design

A USB system has an asymmetric design, consisting of a host controller and multiple devices connected in a tree-like fashion using special hub devices. There is a limit of 5 levels of branching hubs per controller. Up to 127 devices may be connected to a single host controller, but the count must include the hub devices as well. A modern computer likely has several host controllers so the total useful number of connected devices is beyond what could reasonably be connected to a single controller. There is no need for a terminator on any USB bus, as there is for SCSI and some others.


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