USB Universal Serial Bus Tutorial

- a tutorial giving the essential technical details about USB, Universal Serial Bus a widely used computer interface.

USB, or the Universal Serial Bus Interface is now well established as an interface for computer communications.

In many areas it has completely overtaken RS232 and the parallel or Centronics interface for printers, and it is also widely used for memory sticks, computer mice, keyboards and for many other functions.

One of the advantages of USB is its flexibility: another is the speed that USB provides.

USB provides a sufficiently fast serial data transfer mechanism for data communications, however it is also possible to obtain power through the connector and this has further added to the popularity of USB as many small computer peripherals may be powered via this. From memory and disk drives to other applications such as small fans and coffee cup warmers, the USB port on computers can be used for a variety of tasks.

Image of a USB connector showing the basic format
Typical USB connector

USB evolution

The USB interface was developed as a result of the need for a communications interface that was convenient to use and one that would support the higher data rates being required within the computer and peripherals industries.

The first proper release of a USB specification was Version 0.7 of the specification. This occurred in November 1994. This was followed in January 1996 by USB 1.0. USB 1.0 was widely adopted and became the standard on many PCs as well as many printers using the standard. In addition to this a variety of other peripherals adopted the USB interface, with small memory sticks starting to appear as a convenient way for transferring or temporarily storing data.

Summary of USB Versions and Performance
USB Version Details
USB 1 Low speed:   1.5 Mbps
Full speed:   12 Mbps
USB 2 'High Speed' rate of 480 Mbps
USB 3 Raw data transfer rates of 4.8 Gbit/s Read More

Typical USB Flash memory stick

With USB 1.0 well established, faster data transfer rates were required, and accordingly a new specification, USB 2 was released. With the importance of USB already established it did not take long for the new standard to be adopted.

With USB defining its place in the market, other developments of the standard were investigated. With the need for mobility in many areas of the electronics industry taking off, the next obvious move for USB was to adopt a wireless interface. In doing this wireless USB would need to retain the same flexible approach that provided the success for the wired interface. In addition to this the wireless USB interface needs to be able to transfer data at rates which will be higher than those currently attainable with the wired USB 2 connections. To achieve this ultra-wideband UWB technology is used.

USB capabilities

The basic concept of USB was for an interface that would be able to connect a variety of computer peripheral devices, such as keyboards and mice, to PCs. However, since its introduction, the applications for USB have widened and it has been used for many other purposes including, including measurement and automation.

In terms of performance, USB 1.1 enabled a maximum throughput of 12 Mbps, but with the introduction of USB 2.0 the maximum speed is 480 Mbps.

In operation, the USB host automatically detects when a new device has been added. It then requests identification from the device and appropriately configures the drivers. The bus topology allows up to 127 devices to run concurrently on one port. Conversely, the classic serial port supports a single device on each port. By adding hubs, more ports can be added to a USB host, creating connections for more peripherals.

USB advantages & disadvantages

USB has many advantages when compared to other technologies, but it also has a number of disadvantages which need to be considered when deciding on a technology to be used.

Advantages & Disadvantages of USB
  • Ease of use
  • Acceptable data rate for many applications
  • Robust connector system
  • Variety of connector types / sizes available
  • Low cost
  • Data transfer not as fast as some other systems
  • Limited capability & overall performance

USB has many advantages and this is why it is so widely used. However, its simplicity and ease of use, mean that it is not always applicable in applications where more sophisticated interfaces are required for very high speed data transfer.

With USB in almost universal use in new computers, a host of peripherals using the USB standard, its use is set to continue for many years to come. With the USB standard being updated to enable it to keep pace with technology, it could run like a similar story to Ethernet, where it will be in use for many years, but still at the forefront of technology..

By Ian Poole

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