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USB interface grabs a higher version

Posted: 19 Nov 2008 ?? ?Print Version ?Bookmark and Share

Keywords:USB? interface? PCIe?

The commonly used USB interface has now been upgraded to ver 3.0 at a developers' conference where some companies announced product plans for the new specifications with data rates that could hit 400MBps.

USB 3.0 can deliver at least 300MBps of throughput at the application layer. It is backwards compatible with early versions of the specification, however it will need new cabling and connectors and is limited to distances of about 3m, down from 5m for today's USB products.

The 3.0 specification, also called SuperSpeed USB, is unique in several respects. It has five wire cables, having two dedicated transmits and two receive wires and a ground wire, to implement full duplex links at up to 5Gbit/s each way at the PHY. Before, USB employed a two-wire, half-duplex design.

The external appearance of the type-A connector is unchanged, but internally it has five new pins to back full duplex operation. The new connector fits in existing slots.

In rough terms, client USB 3.0 chips would need twice the number of gates and use three times the power of today's USB chips, according to John O'Neill, VP, marketing, Symwave Inc., one of the companies highlighting a USB 3.0 chip at the event.

However, thanks to its high data rates, USB 3.0 exceeds past generations in terms of mW/Gbit transferred, he said. "Additionally, because of the improved protocol, the host burden in processor cycles will be reduced and therefore the overall system power garners even more of an advantage on a mW/Gbit basis," he added.

Indeed, ver 3.0 reduces traffic on the wire, partly to minimize power use. It adopts an interrupt driven protocol, rather than the earlier polling approach. In addition, it communicates via point-to-point links rather than broadcasting data to all connected devices.

The specification also increases the amount of power carried over the link from 500mA to 900mA to more rapidly charge devices via USB. It can now sense a connected devoice with a dead battery and provide a trickle charge to enable the device to come back to life and establish a connection.

The specification is available as a download for those willing to sign a USB adopter's agreement.

"We anticipate discrete host and device controllers could enter the market in mid-2009, and based on those components, we anticipate systems using the specification in early 2010," said Jeff Ravencraft, chairman, USB Implementers' Forum.

The link seeks to extend the widely used interface, initially for applications such as transferring large video files. In the long term, it is expected to be used on the full range of systems now deploying high-speed USB, especially devices with growing flash and disk storage.

Ravencraft said some camcorders now hold up to 250Gbyte of data, and even MP3 players and phones are rapidly growing to house 8Gbyte to 16Gbyte of flash.

In collaboration with the USB 3.0 release, the Personal Computer Memory Card International Association (PCMCIA) group announced the 2.0 ver of its ExpressCard standard for plug in PC devices will be available early next year. The new specification will support transfer rates ranging from two to 10 times faster than ExpressCard 1.2. It backs both the PCIe 2.0 and the new USB 3.0 protocols.

"ExpressCard technology is closely tied to the PCIe and USB specifications, and the 2.0 release of our standard takes full advantage of recent advancements in both interface technologies," said Brad Saunders, chairman, PCMCIA.

Cards based on the updated specification should emerge in early 2010. They may include adapters supporting the 6Mbit/s Serial ATA interface for solid-state drives and USB 3.0 adapters for video transfers and streaming.

More than 400 people attended the USB 3.0 conference. Synopsys announced before the event that its plans to provide silicon cores for USB 3.0 controllers and PHY devices.

Symwave, Inc. announced a USB 3.0 PHY device, the Quasar PHY, which it will display at the show.

The USB 3.0 contributors group has more than 200 companies. More than 10 billion USB devices have shipped to date.

"With more than 2.6 billion USB ports shipped in 2007 alone, the market opportunity for USB 3.0 should eclipse all other wired interconnect technologies combined," said Brian O'Rourke, senior analyst, In-Stat Inc. "The expected compounded annual growth rate for USB 3.0 from 2009-2012 is over 100 percent, reaching over 500 million devices in 2012," he added.

- Rick Merritt
EE Times

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