Simple cPCI question 6U/3U


Can 3U cPCI cards ALWAYS be used in a 6U cPCI system (voltage variations aside)?

I've looked at a number of FAQs and links from the Wikipedia page and I don't see it spelled out.

I know about the 5V and 3.3V variations.

FWIW, I have a GE Defense processor board, which is 6U, with an Elma passive backplane.

Reply to
Spehro Pefhany
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from reading wikipedia I get the impression that that would require that J2 if present on the card be used for the 64 bit expansion and not for task specific purposes,

?? 100% natural 

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Reply to
Jasen Betts

Maybe. If the 3U card is designed to plug into the "standard" PCI bus half of the cPCI connectors, then I think you will have better luck.

At a previous job, we had a 6U cPCI backplane with some custom 6U cPCI cards. However, the cards didn't even have the connectors to plug in to the "standard PCI" part of the bus; they used the "user defined" pins on the other half of the 6U-wide bus to talk to each other.

This caused trouble when they bought a cheap passive 3U cPCI extender, which assumed it was going to be plugged into the "standard PCI" half of the 6U cPCI bus. When it was plugged into the "user defined" half of the 6U cPCI bus, 1) the cards didn't work and 2) the power supply fuses on the extender blew. They ended up buying a fabulously expensive active 6U cPCI extender card from Hartmann to get the cards to work. (They didn't really need the "active" part, but they did need all of the "user defined" pins to pass straight through the extender, which the Hartmann card gave them.)

The cPCI spec is a secret and they charge you more for electronic copies vs. paper, so accurate information is sometimes hard to find. You don't really *need* the spec unless you are designing a cPCI card or backplane. For extra fun, the stuff you need is split up among several documents. Once you need more than about two of the documents, it's actually cheaper to buy the "full pass" and grab everything.

Just another random note: a cPCI x86 single-board computer will present the PCI bus on the "standard PCI" pins, take power from the standard power pins, etc. However, the pins for just about everything else - USB, Ethernet, keyboard, serial, parallel, etc - are specific to manufacturer and even model. This makes it harder to switch vendors, which is intentional. (There *is* a standard for having Ethernet on certain pins, PICMG 2.16, that some vendors support.)

Matt Roberds

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