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USB Port

USB Port. Left side is USB Symbol

About[]

Universal Serial Bus (USB) is a specification to establish communication between devices and a host controller (usually a personal computer), developed and invented by Ajay Bhatt, while working for Intel. [1] USB has effectively replaced a variety of interfaces such as serial and parallel ports.

USB can connect computer peripherals such as mice, keyboards, digital cameras, printers, personal media players, flash drives, Network Adapters, and external hard drives. For many of those devices, USB has become the standard connection method.

USB was designed for personal computers, but it has become commonplace on other devices such as smartphones, PDAs and video game consoles, and as a power cord. As of 2008, there are about 2 billion USB devices sold per year, and approximately 6 billion total sold to date.[2]

Unlike the older connection standards RS-232 or Parallel port, USB connectors also supply electric power, so many devices connected by USB do not need a power source of their own.

Pin out[]

USB Pin Out and Wiring
Pin Name Cable Color Description
1 VCC Red +5 VDC
2 D- White Data -
3 D+ Green Data +
4 GND Black Ground


USB is a serial bus. It uses 4 shielded wires: two for power (+5v & GND) and two for differential data signals (labelled as D+ and D- in pinout). NRZI (Non Return to Zero Invert) encoding scheme used to send data with a sync field to synchronise the host and receiver clocks. In USB data cable Data+ and Data- signals are transmitted on a twisted pair. No termination needed. Half-duplex differential signaling helps to combat the effects of electromagnetic noise on longer lines. Contrary to popular belief, D+ and D- operate together; they are not separate simplex connections.

Version history[]

Prereleases[]

  • USB 0.7: Released in November 1994.
  • USB 0.8: Released in December 1994.
  • USB 0.9: Released in April 1995.
  • USB 0.99: Released in August 1995.
  • USB 1.0 Release Candidate: Released in November 1995.

USB 1.0[]

  • USB 1.0: Released in January 1996.
    Specified data rates of 1.5 Mbit/s (Low-Bandwidth) and 12 Mbit/s (Full-Bandwidth). Does not allow for extension cables or pass-through monitors (due to timing and power limitations). Few such devices actually made it to market.
  • USB 1.1: Released in September 1998.
    Fixed problems identified in 1.0, mostly relating to hubs. Earliest revision to be widely adopted.

USB 2.0[]

  • USB 2.0: Released in April 2000.
    Added higher maximum bandwidth of 480 Mbit/s [60 MB/s] (now called "Hi-Speed"). Further modifications to the USB specification have been done via Engineering Change Notices (ECN). The most important of these ECNs are included into the USB 2.0 specification package available from USB.org:
    • Mini-A and Mini-B Connector ECN: Released in October 2000.
      Specifications for Mini-A and B plug and receptacle. Also receptacle that accepts both plugs for On-The-Go. These should not be confused with Micro-B plug and receptacle.
    • Errata as of December 2000: Released in December 2000.
    • Pull-up/Pull-down Resistors ECN: Released in May 2002.
    • Errata as of May 2002: Released in May 2002.
    • Interface Associations ECN: Released in May 2003.
      New standard descriptor was added that allows multiple interfaces to be associated with a single device function.
    • Rounded Chamfer ECN: Released in October 2003.
      A recommended, compatible change to Mini-B plugs that results in longer lasting connectors.
    • Unicode ECN: Released in February 2005.
      This ECN specifies that strings are encoded using UTF-16LE. USB 2.0 did specify that Unicode is to be used but it did not specify the encoding.
    • Inter-Chip USB Supplement: Released in March 2006.
    • On-The-Go Supplement 1.3: Released in December 2006.
      USB On-The-Go makes it possible for two USB devices to communicate with each other without requiring a separate USB host. In practice, one of the USB devices acts as a host for the other device.
    • Battery Charging Specification 1.1: Released in March 2007 (Updated 15 Apr 2009).
      Adds support for dedicated chargers (power supplies with USB connectors), host chargers (USB hosts that can act as chargers) and the No Dead Battery provision which allows devices to temporarily draw 100 mA current after they have been attached. If a USB device is connected to dedicated charger, maximum current drawn by the device may be as high as 1.8A. (Note that this document is not distributed with USB 2.0 specification package only USB 3.0 and USB On-The-Go.)
    • Micro-USB Cables and Connectors Specification 1.01: Released in April 2007.
    • Link Power Management Addendum ECN: Released in July 2007.
      This adds a new power state between enabled and suspended states. Device in this state is not required to reduce its power consumption. However, switching between enabled and sleep states is much faster than switching between enabled and suspended states, which allows devices to sleep while idle.

USB 3.0[]

The USB 3.0 Promoter Group announced on 17 November 2008 that version 3.0 of the specification had been completed and had made the transition to the USB Implementers Forum (USB-IF), the managing body of USB specifications.[3] This move effectively opened the specification to hardware developers for implementation in future products. The first USB 3.0 consumer products were announced and shipped by Buffalo Technology in November 2009, while the first certified USB 3.0 consumer products were announced 5 January 2010, at the Las Vegas Consumer Electronics Show (CES), including two motherboards by ASUS and Gigabyte Technology.[4]Manufacturers of USB 3.0 host controllers include, but are not limited to, Renesas/NEC Electronics, Fresco Logic, Asmedia, Etron, VIA Labs and Texas Instruments. As of November 2010, Renesas is the only company to have passed USB-IF certification, although motherboards for Intel's Sandy Bridge processors have been seen with Asmedia and Etron host controllers. On October 28, 2010 Hewlett-Packard released the HP Envy 17 3D featuring a Renesas USB 3.0 Host Controller several months before some of their competitors. AMD is working with Renesas to add its USB 3.0 implementation into its chipsets for its 2011 platforms. At CES2011 Toshiba unveiled a laptop called "Toshiba Qosmio X500" that included USB 3.0 and Bluetooth 3.0, and a new series of Sony VAIO laptops that will include USB 3.0. The new models in the Dell XPS series are to include USB 3.0.

References[]

  1. Sutter. John, D.,. USB inventor is tech's unlikely 'rock star'. CNN.com. 2010-02-04. Retrieved 2010-05-27.
  2. Perenson, Melissa J., SuperSpeed USB 3.0: More Details Emerge. PCWorld. 6 Jan 2009.
  3. USB.org. http://www.usb.org/press/USB-IF_Press_Releases/2008_11_17_USB_IF.pdf accessdate=2010-06-22
  4. PC Worl. http://www.pcworld.com/article. accessdate=2010-06-22


Links[]

See also[]

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