Proposed instrument bus aims for 6-Gbyte/s systems
Presented last month by the PXI Systems Alliance industry group (San Diego, CA), the PXI Express (PXIe) spec would provide test systems with backplane bandwidths up to 6 Gbytes/s�an improvement of more than 45 times over traditional 132-Mbyte/s PXI systems. The capability should allow test systems built around PXIe boards�which are less expensive than standalone instrument configurations�to perform measurements for high-bandwidth communications, video, and large, multichannel data acquisition applications that could not previously be handled by PXI systems.
Adding the necessary channels for timing and control, the PXIe bus is built upon the CompactPCI Express data bus, which was designed for Intel-based PCs and released in August. Key to the performance of both buses is the use of 32 differential-signaling pairs to provide the by-8 link and synchronization signals. The high-speed link will allow test data to be moved rapidly from fast digitizers to the broad memories of host systems, thereby allowing detailed capture of high-frequency signals or numerous sensor inputs.
The PXIe specification's authors have taken a “no board left behind” approach, so that the first PXIe systems�scheduled to make their appearance early in 2006�will allow PXI boards to be plugged into so-called hybrid slots on card chassis. For the hybrid slot, the connector for the PXIe differential pairs is placed in an area between where connectors for the single-ended data and system timing lines are located on typical PXI cards. Thus the slot can take both types of cards.
To explain how the hybrid slot works, the specification's authors describe an eight-slot chassis containing a system slot, three PXIe hybrid slots, and four ordinary PXI slots. Communication between the different cards is taken care of by a PCIe-to-PCI bridge�which changes the PXI data lines to differential pairs�and the system slot's two by-8 connectors: one for PXI cards and the other for PXIe boards.
For more information, call Fred Bode of the PXI Systems Alliance at 619-297-1213, or e-mail , or visit .
�Richard Comerford
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