USB tutorial
- an overview or tutorial about USB, the Universal Serial Bus or interface
that is almost universally accepted for many computer data communications.
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.
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.
With USB 1.0 well established, faster data transfer rates
were required, and accordingly a new specification, USB 2 was released. Wit 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 connections and cables
The USB connector is remarkably simple having just four main connections for the
data and power. In addition to this it is also possible to use extender cables.
The maximum allowable length for an individual cable is 5 metres (3 metres for
slow devices) and this allows the USB data acquisition module to be located
remotely from the computer.
A USB cable has two forms of connector. These are designated
the "A" and "B" connectors. The connections to the connectors are given below:
| Pin |
Function |
| 1 |
Vbus
4.75 - 5.25 V |
| 2 |
Data - |
| 3 |
Data + |
| 4 |
Ground |
| Shell |
Screen |
USB cable pin assignments
USB tutorial summary
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. However only time will tell.
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