The convergence of different types of smart computing and consumer devices, in conjunction with new media formats and large and inexpensive storage, means that user applications now require significantly more bus bandwidth to meet increasing demands for fast data connectivity between PCs, peripherals and a myriad of consumer devices. The new USB 3.0 or SuperSpeed USB standard is designed to address this need for faster data connectivity by adding a substantially higher transfer rate and improved interaction between, for example, a mobile consumer device and the host computer.
As is well known, the low-cost bidirectional USB interface is all-pervading in its different physical form factors and is probably the most successful interface in the history of computers. The USB 1.1 and 2.0 standards have been around since the late 1990s, achieving almost 100% market acceptance in PCs. The latest standard, USB 3.0, is nothing like as ubiquitous, at least not yet; over three years after its release in late 2008. Although adoption has been initially slow, more and more USB 3.0 certified products are becoming available on the market offering ‘SuperSpeed’ transfer rates and improved power capabilities. Many of these new high-speed data storage devices can be purchased today in large electrical high street stores.
USB 3.0 delivers a data transfer rate of around 4.7Gbit/s — a tenfold increase over the USB 2.0 (Hi-Speed USB) 480Mbit/s rate, opening up more headroom for demanding applications such as high-definition full-frame 1080p video.
Figure 1: Advantages of USB 3.0 over USB 2.0 include a 10x increase in data rate and 50% more bus power.
Other key elements are fast ‘sync-n-go’, minimising user wait-time, and optimised power capabilities resulting in around one-third the power usage of USB 2.0 overall. USB 3.0 uses a new interrupt-driven protocol rather than ‘device polling’, which means that non-active devices will not have their power drained by the host controller as it searches for active data transfer. Additionally, the total power output has been increased from around 100mA up to 900mA, which means that more than four devices can be powered from a single hub, and devices such as an external Blu-Ray writer will not require an external power supply.
Furthermore, a new power delivery specification to extend the use of micro-USB 3.0 connectors for battery charging applications has been created. This enables voltage and current values to be negotiated over the USB power pins to deliver power up to 100W.
Importantly, SuperSpeed USB is backwards compatible with USB 2.0. As was the case with the upgrade from USB 1.1 to 2.0, the new USB 3.0 connectors and cables are physically and functionally compatible with the hardware of the previous specifications. So USB 3.0-enabled devices will operate with products equipped with USB 2.0, and will not damage the PC or device, although clearly the USB 3.0 features such as the SuperSpeed data rate will not work.
Figure 2: The dual bus architecture of USB 3.0 is backwards compatible with USB 2.0 devices, but not at SuperSpeed data rates.
Although the core architectural elements remain from the previous standards, several changes have been made to support a dual bus arrangement. The compatibility of the new specification is in the new connector design. USB 2.0 worked via four lines: a pair for input/output data, one line for power, and one for ground. USB 3.0, however, adds five additional lines: two SuperSpeed transmit and two SuperSpeed receive lines, enabling the simultaneous sending and receiving of data, plus an additional ground pin. (Table 1 shows the USB 3.0 pinout.)
However, these new contacts are not physically placed adjacent to the existing pins, but sit parallel to the existing ones on a different plane, recessed into the back of the plug. Containing nine wires, the USB 3.0 cable is also considerably thicker.
For manufacturers looking to include the functionality and advantages of USB 3.0 connectivity into their new product designs, Cyntech Components carries a full range of USB 3.0 connector types, including USB-A, USB-B, mini-USB and micro-USB male and females types.
Author profile: Dave Mellor is Director, Cyntech Components