VPX Hybrid Backplanes

VPX is a new high-performance VME architecture using switched serial fabrics in typically a mesh topology which offers tremendous bandwidth potential. While different from the traditional VME64 P0/P1/P2 backplane architecture, VPX can be compatible with legacy systems in “hybrid” backplanes.

First, let’s take a look a few of the differences of VPX and VME64x backplane. VME64x uses the VME parallel bus across a 160-pin DIN connector. The slot-to-slot bandwidth of VME64x is approximately 80 Mbytes/sec. The slot-to-slot bandwidth of VPX is approximately 5,000 Mbytes/sec. The VME connectors are ideal for single ended signals but the VPX architecture uses the wafer-based MultiGig connector that has much greater bandwidth and can support either differential or single ended signals. One of the most important differences is that VME64x has only 110 undefined pins available in the J1/J2 connectors and a total of 205 pins if you include the 95 P0 pins. However, VPX has 480 pins per slot that could be assigned by the user or they could be used as 186 differential pairs. This is because the connectors J1 - J6 have no required (defined) use. The backplane in Photo 1 shows the physical differences of the connectors. With a robust high-speed differential connector and direct point-to-point mesh connections, VPX allows much higher performance than VME64x. However, real-time determinism of VME64x, along with its mature and well understood architecture, vast product ecosystem, and backwards compatibility to legacy VME (such as VME32 and earlier) has its advantages. Combining VPX and VME64x can be a powerful combination.

VME Compatibility

There are many benefits to having some compatibility with VME. It saves time and costs in software rewriting, re-use of drivers, as well as hardware. There are savings in terms of costs and training/learning curve in re-using legacy cards. Many users in the same Mil/Aero key market are highly familiar with VME. Hybrid systems supporting VME/VPX may make some customers more comfortable with the move to VPX. It sounds funny, but it’s amazing how VME can give a customer that “warm, fuzzy feeling”. This of course, is a testament to VME’s longevity and success in applications and military programs that run for ten years or more.

Design Flexibility

One compelling feature of VPX is that is has a lot of design flexibility. The architecture can simultaneously support a mix of bus segments including full mesh, pipeline or single or dual star topologies. Connector segments J1 to J6 can even be implemented for either differential signals or single ended signals. The architecture offers design flexibility as opposed to a more fixed and defined architecture. This allows a user to use exactly as many pins and connection configurations, etc, as are needed for the specific application. VPX designs a standard card layout and standard mechanics but lets system engineers connect-the-dots between them so as to conform to the exact needs of their requirement.

Overall, VPX Hybrids offer the best of both worlds -- powerful VPX performance and a bridge to legacy VME.

Melissa Heckman
Electrical Engineer
Elma Bustronic

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