The VPX (VITA 46) standard continues it rapid entrÈe into the aerospace and defense market. Board-level modules based on this advanced high-bandwidth, highly rugged board architecture have already been tapped as the standard modules for important new programs such as the Armyís Future Combat Systems (FCS). Defined and developed by the cooperative effort of numerous military system prime contractors, COTS vendors, and military customers, VPX extends the proven ìgoodnessî of the venerable VME ecosystem, including form factors and support for VME electrical signals as well as standard mezzanines such as PMC and XMC. It also provides bandwidth, high-speed switched serial fabric support, and levels of ruggedization previously unavailable. Also rendered is the Line Replaceable Module (LRM) in-the-field maintenance needed to address 21^st-century application requirements.

Various VPX working groups, under the auspices of the VITA Standards Organization (VSO), are now hard at work advancing the utility of the VITA 46 and VITA 48 (VPX-REDI) standards. The working groups are defining and preparing for ANSI accreditation a wide array of ìdot-specsî beyond the already ANSI-approved base standard. These new dot-specs will add open standards for VPX to support a variety of fabrics, I/O, and infrastructure. Figure 1 shows a pictorial of VPX dot-specs. Meanwhile, our discussion focuses on VPXís VITA 46.9, 46.10, 46.12, and 46.14 dot-specs.

Figure 1 (click graphic to zoom by 1.9x)

VITA 46.9 maps signals

VITA 46.9 (PMC/XMC/GbE Signal Mapping to 3U/6U on VPX User I/O Connector) defines signal mapping for all PMC, XMC, and GbE. This standard will be unique when finalized because it will be the first in the industry to map the high-speed differential I/O provided by XMC mezzanine module I/O to a backplane, a function not available from VME or any other standard to date. Military applications typically need rear I/O, unlike telecommunications applications, which favor front-panel I/O. The standard ensures a stable standard for PMC, XMC, and GbE, without which vendors might otherwise implement unique pinout schemes causing market fragmentation and increasing the likelihood that cards from different vendors would not interoperate.

VITA 46.9 dot-spec system integrators designing with VPX will more easily and quickly be able to add high-speed serial communications, graphics, SATA drives, and 10 GbE to their products. VITA 46.9 will also standardize where GbE signals are located on the VPX connector. The VITA 46.9 working group has completed its working group ballot and is working through the final comments. The standard should complete ANSI balloting in Q2 of 2009.

VITA 46.10ís RTM

VITA 46.10 (Rear Transition Module on VPX) defines the use of a Rear Transition Module (RTM) for VPX. This RTM enables the integration of VPX development systems using air-cooled cards, and in advance of custom backplane availability during development of conduction-cooled card systems. The RTM enables data to be easily taken out of the back of the system, speeding system development and time to market. VPX systems using the high-speed wafer-style connector, the Tyco MultiGigRT2, are used with an RTM. Using an RTM, which enables interface with standard connectors, reduces development costs for system integrators because they will not need to commit to a particular backplane configuration before advancing their development stage.

VITA 46.12 and fiber optics

The VITA 46.12 (Fiber Optics on VPX) standard defines the use of fiber optics with VPX. A defined standard approach for the use of fiber optics is highly desired because of the advantages that fiber optics provide in comparison to copper cabling. Unlike copper cabling, fiber optic cabling is immune to EMI and lacks detectable electromagnetic emissions. Fiber optic cabling also weighs less than copper cabling and can transmit high-speed signals over greater distances than equivalent copper connections. To support fiber, VITA 46.12 assigns the location of the P5 and/or P6 VPX connector as the home for the fiber optic connector, which can be either the Mechanical Transfer (MT), Expanded Beam (EB), or LuxCis-type of connectors designed for ARINC 801. These three types of fiber optic connectors each have specific attributes and unique advantages:

n Mechanical Transfer (MT) – The MT type uses a self-aligning pair of mating shells and pins to maintain positional accuracy of fibers in the form of a ribbon cable (Figure 2). MT is an established commercial standard offering high-connection density, but needs care to maintain cleanliness and does not provide specific alignment of individual fibers.

n Expanded Beam (EB) – This uses a spherical lens at the end of each fiber to expand the beam to many times its size. Connection is made by bringing the two lenses into close proximity without physical contact. EB connectors are less sensitive to alignment or contamination and can tolerate many mating cycles without degradation. An EB fiber interface is shown in Figure 3.

n LuxCis-type/ARINC 801 connectors – These consist of metal shell pairs containing multiple signal connections using ceramic ferrules for fiber alignment, maintaining positional accuracy in high-vibration environments.

Figure 2 (click graphic to zoom by 1.5x)

Figure 3 (click graphic to zoom by 1.9x)

The VITA 46.12 working group is collaborating with two leading connector vendors, Amphenol and Tyco, to explore supporting a single fiber optic connector type for use with VPX. If successful, this cooperation will help ensure the rapid growth of the marketís use of fiber optic cables with VPX, enabling users to take full advantage of the technologyís higher bandwidth, noise immunity, and support for greater-length cables than is available with copper. The working group has agreed on and completed drawings for the MT and EB style connectors and is currently completing the drawings for the ARINC 801 connector. The working group expects to finish its work at the end of Q2 2009 and then proceed to the ANSI ballot process.

VITA 46.14: Interconnects

The VITA 46.14 (RF Interconnect on VPX) standard defines the use of RF connectors over the backplane. This flexibility is especially useful for applications requiring high-speed analog signals such as radar front-ends and radio tuners. Work on this standard has recently started. This standard supports the use of coax cable instead of the less desirable discrete wire connectivity. Coax cable provides better signaling, higher data rates, less noise, and less crosstalk than discrete wire. VME did not support RF over the backplane, so instead it was typically provided via the front panel with coax cable on VME. With VITA 46.14, VPX users can implement a standard approach for coax cable on the backplane.

Additional VITA standards development

In addition to VITA 46.9, 46.10, 46.12, and 46.14, progress also continues apace on a number of other VPX dot-specs. One of these is VITA 46.11 (System Management on VPX), which defines an easy-to-implement protocol to mitigate hardware obsolescence and maximize IP portability. VITA 46.20 (Switch Slot Definition on VPX) and VITA 46.21 (Distributed Switching on VPX) will, respectively, define centralized and distributed switch architectures. VPX was developed from its inception with the intention to support multiple switching topologies, and the VITA 46.0 base standard already provides guidance for a five-slot topology. With the completion of VITA 46.20 and 46.21, VPX users will have dot-specs that standardize switching architectures using a centralized card through which all other cards are routed prior to being switched. They will also have distributed architectures beyond five slots that do not require the dedicated slot used in the centralized approach. A working group ballot for these standards is expected in Q2 2009.

Jing Kwok is principal engineer in the Technology Group at Curtiss-Wright Controls Embedded Computing. He has been involved with VMEbus standards work for the past 15 years. He is editor of one of the VITA 46 dot-specs now in working group ballot and was one of the chapter editors for the VME64 specification. Jing is a graduate of the British Columbia Institute of Technology. He can be contacted at jing.kwok@curtisswright.com.

Curtiss-Wright Controls Embedded Computing

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For more information on the latest VITA standards and their statuses, go to www.vmecritical.com and click on the ìVITA standardsî link.