PXI Express
The PXI Systems Alliance has passed specification PXI-5, which specifies how to integrate PCI Express performance into both CompactPCI and PXI while preserving backward compatibility. Because PXI is based on CompactPCI, work began first on CompactPCI Express in early 2004. The CompactPCI Express specification defines the fundamental mechanical and electrical features of CompactPCI Express systems and, therefore, PXI Express systems. This includes the selection of connectors to support PCI Express, definitions of slots and board mechanicals, definitions of slot/board electrical signals, and compliance-testing requirements. The CompactPCI Express specification was released on June 27, 2005 and the PXI Express specification was completed in August 2005. PXI Express incorporates CompactPCI Express technology with enhancements for PXI compatibility, timing and synchronization, and system software frameworks.
The attached figure shows the basic layout of a CompactPCI/PXI Express backplane and illustrates how PCI Express is integrated into backplanes while preserving compatibility with current PXI modules. PCI Express electrical lanes run from the system slot (either an embedded controller or MXI link) to the hybrid slots, providing a high-bandwidth path from the controller to the backplane slots. In addition, the installation of an inexpensive PCI Express-to-PCI bridge on backplanes provides PCI signaling to all PXI and PXI Express hybrid slots. This ensures compatibility with PXI modules on the backplane. The system controller slot is capable of supporting up to a x16 PCI Express link, plus a x8 link, providing a total of Template:5,5 GByte/s transfer capacity to the PXI backplane. This is a more than 45 times improvement in PXI backplane throughput.
A key new feature is the PXI Express hybrid slot, which delivers support for both PCI and PCI Express signaling by taking advantage of available pins on the high-density backplanes. This creates a level of backward compatibility not available in even desktop PC card-edge connectors. In this hybrid peripheral slot, you can install PXI modules that use PCI signaling, as well as future high-performance PXI Express modules, in the same slot. However PXI modules that have implemented the J2 backplane connector require minor factory modification by the instrument vendor to allow operation in the PXI Express hybrid slot (the majority of PXI cards implement J2).
PCI Express uses the same driver and OS model as PCI, which ensures complete software compatibility among PCI-based systems (such as PXI) and PCI Express-based systems (for example, PXI Express). Neither vendors nor customers need to revise driver software or application software for PCI Express-based systems. Therefore, in addition to providing hardware compatibility through the hybrid slot, PXI Express systems also help engineers preserve existing software investments.
Read more about this topic: PCI E Xtensions For Instrumentation
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