Electronic Design

USB 2.0 At A Glance

USB is an easy to use, royalty-free technology for the PC and related peripherals. This universal, plug-and-play technology is so widely used that it's expected to completely replace the expensive, nonstandard proliferation of serial, parallel, and game interfaces found in legacy PC systems.

With the development of USB 2.0, manufacturers can now extend USB technology to support the higher-speed peripherals that are increasingly in demand. The USB 2.0 specification is being developed and promoted by the USB 2.0 Group, which comprises seven core companies: Compaq, Hewlett-Packard, Intel, Lucent Technologies, Microsoft, NEC, and Philips. This group was incorporated into a nonprofit organization in March 2000.

The USB 2.0 group envisions that the future PC may simply be a sealed box with multiple USB hub-ports for external connections. USB 2.0 is designed to be backward compatible with low-speed (1.5 Mbits/s) and full-speed (12 Mbits/s) USB implementations. Also, USB 2.0 uses USB 1.1-compliant cables to provide a painless migration path for users, a simpler, less-expensive peripheral solution for PC manufacturers, plus expanded performance for peripheral manufacturers.

Support of higher-speed USB 2.0 peripherals connected to a hub assumes the use of USB 2.0 hubs. The transmission speed is negotiated on a device-by-device basis. If the higher 480-Mbit/s speed isn't supported by a peripheral, then the link operates at a lower speed of 12 Mbits/s or 1.5 Mbits/s as determined by the peripheral.

For example, in a configuration where a high-speed video-conferencing camera employs USB 2.0 and several slower USB peripherals, such as a printer, mouse, and keyboard, then each will be supported at the appropriate data rate. Any downstream port of a USB 2.0 hub can support a USB device of any speed.

USB 2.0 Milestones:

  • 1995—USB 2.0 announced with 360-Mbit/s target speed
  • Q4 1999—USB 2.0, r 0.9 issued with 480-Mbit/s target speed
  • Q2 2000—480 Mbit/s speed demonstrated
  • Q2 2000—USB 2.0, Release 1.0
  • For more information about USB 2.0, visit the web site at www.usb.org.

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