In sci.electronics.design Spehro Pefhany said:
Can 3U cPCI cards ALWAYS be used in a 6U cPCI system (voltage
variations aside)?
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.)
I've looked at a number of FAQs and links from the Wikipedia page and
I don't see it spelled out.
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.
FWIW, I have a GE Defense processor board, which is 6U, with an Elma
passive backplane.
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
