Why Technical English

Universal serial bus (USB) | January 22, 2009

By Jiří Sekera

Dear friends of Technical English,

Here is another technical text written by my student. I think the text can be a good pattern of technical writing. Moreover, the text contains very useful information, which might be interesting for people communicating via the Internet. Galina Vitkova

USB is the most widespread connector for connecting external devices to a computer. It’s used to connect devices like printers, keyboards, mice, digital cameras, game implements etc. USB is a successor of the older means of connecting like serial or parallel ports, PS/2, game ports and others.

Conception of USB was developed within cooperation of the companies Compaq, Hewlett-Packard, Intel, Lucent, NEC, Microsoft and Philips.

There are two basic types of connectors: type A (USB host) and type B (USB device).

obr2-2400Nowadays we have also mini or micro connectors, which are used in digital cameras, mobile phones or in mp3 players.

The scheme of the cable in this case is depicted below:

obr1-24001

Pin

Name

Colour

Descript.

1

VBus

Red

5 VDC

2

D-

White

Data –

3

D+

Green

Data+

4

GND

Black

Ground


Legenda

Vbus – is used for control of the host by a computer

D– is used for setting of devices

D+ is used for setting of devices

GND – ground cable

VDC – special mark of volts

USB has two versions, USB 1.1 and USB 2.0, which principally differ from each other just by the speed of transfer.

USB 1.1 has two types of the speed:

  • a low-speed bus (the maximum speed of transfer is 1,5 Mbit/s);
  • a full-speed bus with the maximum speed of transfer 12 Mbit/s.

USB 2.0 ensures connecting hi-speed devices (the maximum speed of transfer 480Mbit/s). These devices are connected in the same way as the full-speed devices, change of transfer speed is solved by software.

Besides the speed it is necessary to distinguish a type of the power source:

  • Bus-powered devices are supplied directly from a bus.
  • Self-powered devices have their own power source.

Basic characteristics

  • The data cable cannot be longer than 5 metres; if it is longer, it can cause problems with data transfer.
  • Plug & play means that we can connect devices without installation of drivers.

Alternatives and the future

The alternative type of the connection is the FireWire (IEEE 1394) provided by the Apple Company, which has the maximum speed of transfer 800Mbit/s. It’s being used to transfer videos from digital cameras, but it isn’t too widespread.

In the future there should be USB Wireless. Its hypothetic speed of transfer is 110Mbit/s at a distance of 10 metres up to 480Mbit/s at a distance of 3 metres. A new version with the maximum speed 4,8Gbit/s is also developed.

.

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1 Comment »

  1. […] Universal serial bus (USB)   […]

    Pingback by Changing the theme of this blog « Why Technical English — August 26, 2010 @ 9:26 am


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