Only two weeks ago, I commented that USB is a popular topic. In the last few years, any event or publication that we run/publish on USB seems to draw a crowd. I think that part of the attraction is that it is a well-established, widely-utilized standard, but also it does not stand still. Engineers naturally want to keep up with the new developments.
Although USB 2.0 has served us well for numerous applications for many years, the need for greater capacity, speed etc. drove the development of USB 3.0. In recent weeks, both AMD and Intel have announced USB 3.0 support in their chip-sets, so it follows that it will become commonplace in PC in the not too distant future. That implies that USB 3.0 peripherals will be in demand and, of course, they tend to be embedded systems …
The key benefit of USB 3.0 is speed. Along with the three speeds offered by USB 2.0 [Low Speed, Full Speed and High Speed], USB 3.0 adds SuperSpeed, which promises data transfer 10X faster than before. The other particularly noticeable benefit is bus power. It has become increasingly common to find devices that connect to a PC via USB and also draw all their power from the interface. For example, I have several external disk drives and a flatbed scanner that all afford me this convenience. With USB 3.0, the available power is almost doubled, which increases the scope for application of the facility.
The implementation of USB is somewhat complex, as the current USB wiring would not straightforwardly support higher speeds. USB 3.0 cables feature 4 extra wires to carry SuperSpeed data traffic, in addition to the 2 used by USB 2.0 for the other speeds. A single pair of wires is needed to send data. In addition to higher speed, SuperSpeed is bidirectional – data can go up and down the bus simultaneously – hence the 4 wires. Earlier USB implementations were all unidirectional. This change means that new cables and connectors are required. The good news is that there is reasonable backwards compatibility – older USB plugs can be accommodated by USB 3.0 sockets. Building a USB network using equipment that supports different versions is somewhat complex. For example, a USB 3.0 hub can only offer downstream SuperSpeed data transfer if there is unbroken support for SuperSpeed upstream to the host. Ultimately this is not a serious limitation.
Next week I will be at the Embedded Systems Conference in San Jose, California. I have a paper in the conference [which will actually be delivered by a very competent colleague] covering USB, with an emphasis on USB 3.0. I will also be hosting a Web seminar on the topic shortly. I strongly suspect that this will be a popular conference topic over the next year.
Posted April 25th, 2011, by Colin Walls
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