TECH LIBRARY

Universal Serial Bus

USB (Universal Serial Bus) is a way of setting up communication between a computer and peripheral devices. USB is intended to replace many varieties of serial and parallel ports. USB can connect computer peripherals such as mice, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers, personal media players, flash drives, and external hard drives.

Signaling

USB supports following signaling rates:

Rate

Maximum Speed

Information

Low Speed

1.5 Mbit/s

This rate is defined by USB 1.0. It is very similar to "full speed" operation except each bit takes 8 times as long to transmit. It is intended primarily to save cost in low-bandwidth human interface devices (HID) such as keyboards, mice, and joysticks.

Full Speed

12 Mbit/s

This rate is the basic USB data rate defined by USB 1.1. All USB hubs support full speed.

Hi-Speed (USB 2.0)

480 Mbit/s

This rate was introduced in 2001. All hi-speed devices are capable of falling back to full-speed operation if necessary; they are backward compatible. Connectors are identical.

SuperSpeed (USB 3.0)

5.0 Gbit/s

The USB 3.0 specification was released by Intel and partners in August 2008, according to early reports from CNET news. The first USB 3 controller chips were sampled by NEC May 2009 and products using the 3.0 specification are expected to arrive beginning in Q3 2009 and 2010. USB 3.0 connectors are generally backwards compatible, but include new wiring and full duplex operation. There is some incompatibility with older connectors.