VME, VPX and VXI Extenders

VME, VPX and VXI extenders are boards that are used to improve or extend the functionality of standard VME, VPX, and VXI cards. Basic parameters include type, height, and length. System, form factor, and operating system specifications are also important to consider. Features for VME, VPX, and VXI extenders include on-board current-to-voltage conversion, ejector or injector latches, on-board 3.3-V regulator, 5-V to 3.3-V translators, and short circuit protection. Some VME, VPX and VXI extenders are hot-swappable and provide protection against electromagnetic interference (EMI) and radio frequency interference (RFI). Others have logic analyzer ports and are certified by regulatory bodies such as the U.S. Federal Communications Commission (FCC). 

There are three basic types of VME, VPX and VXI extenders: text, hot swap, and form factor. Text extenders or passive extenders are designed to bring a board completely out its chassis, card cage or enclosure so that testing or debugging can be performed. These VME, VPX, and VXI extenders substantially increase the testing space. Hot swap extenders allow a standard VME, VPX, or VXI card to be inserted and removed from a working VME, VPX, or VXI system without disturbing the normal operation, or without damaging the system or the board. Form factor extenders allow boards of different depths to be used in the same depth card cage or chassis. For example, a 60-mm board fitted with a 160-mm form factor extender can plug into a system designed for 220-mm deep boards. 

Selecting VME, VPX and VXI extenders requires an analysis of technologies and form factors. Technology choices include VMEbus, VME64, VME64x, VME160, VME320, VPX and VXIT. The original VersaModule Eurocard bus (VMEbus) uses rugged circuit boards that provide a 96-pin plug instead of an edge connector for durability. The other, numbered VME choices are variants of this original standard. VPX (aka VITA 46) is an American National Standards Institute (ANSI) standard based on the VMEbus with support for switched fabric using a high speed connector. VXIT^M (VMEbus eXtensions for Instrumentation) is a platform trademarked by National Instruments and a consortium of other companies to define a multivendor instrument-on-a-card standard for industrial applications. Other technologies for VME, VPX and VXI extenders may also be available. 

There are several form factors for VME, VPX and VXI extenders. The original VMEbus specification recognizes two types of cards: 3U and 6U.  3U cards, also known as single height boards, are 100 mm x 160 mm with one 96 pin DIN connector (J1 connector) on the rear that plugs into the backplane. 6U cards, also known as double height boards, are 233 mm x 160 mm with a second 96 pin DIN connector (J2 connector). For VXI systems, cards are lettered from A to D. Size A cards are 100 mm (3U) x 160 mm. Size B cards are 233 mm (6U) x 160 mm. Size C cards are 233 mm (6U) x 340 mm. Size D cards are 360 mm (9U) x 340 mm. VXI cards have a height of 360 mm (9U) and a length of 400 mm. Other unlisted form factors for VME, VPX and VXI extenders may also be available. .

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