Saturday, November 1, 2008

Running an Advanced MC

By Herbert Reich

Often referred to as advanced MC, advanced mezzanine cards are essentially printed circuit boards. The PICMG (PCI Industrial Computers Manufacturer's Group) is made up of more than one hundred companies and has a significant effect on standards for electronics production. Advanced MC is targeted to the requirements of the next generation of carrier grade equipment for communications devices. These specifications have been designed to work with any of the available carrier cards (though primarily with AdvancedTCA), and to plug into backplanes directly (as defined by the MicroTCA spec).

Advanced MCs are defined as carrier cards. Intermediate revisions of the specification are called ECNs or engineering change notices. They include R1.0, which was adopted in January 2005, ECN-001, adopted in June of 2006, and R2.0, adopted in November 2006. Advanced MC cards can use a number of AMC specifications, include PCI Express and PCI Express Advanced Switching (AMC.1), Gigabit Ethernet and XAUI (AMC.2), Storage (AMC.3) and Serial RapidIO (AMC.4). Advanced MC cards can also use proprietary signaling based in LVDS.

There are approximately six different types of Advanced MC cards. Full-sized modules are the most commonly seen, allowing components up to twenty-three and a quarter millimeters high. Mid-sized modules allow component heights from a little over eleven and a half millimeters to a little more than fourteen millimeters, depending on the location of the board. Compact modules permit a height of only a little more then eight millimeters. To hold a single full sized module or two compact sized modules, a special carrier card is required. This card is called a cutaway or hybrid carrier.

Depending on the number of filled slots on a given board, the height can be paired with either a single or double width. Double width cards allow for more space for components, but they don't offer increased bandwidth or power, since a single connector is still used. The Advanced MC connector has a relatively complex pinout, using up to one hundred seventy traces in four different length. This allows hot swapping, provided it's known in advance in which order which traces will become active. Cards may require traces on one side only, which reduces cost for mass production. Using only half of the available pin locations, combined with the various height options, results in four different types of connectors available on a carrier card.

Advanced MC cards capable of being the only requirement for processing functionality. Because of this, the MicroTCA standard was developed, aimed at supplying a chassis that would let these cards work without a carrier cards. Multiple companies have launched products since the July 2006 approval date of this standard. Advanced MC has offered a great deal of flexibility and technological advancement in the communications field. There are more options for manufacturers than ever before, given the versatility of this specification.

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