On Sat, Oct 22, 2005 at 10:04:26PM -0400, Jack Carroll wrote:
> The standard for PMC should be available from www.vita.com. They
> originally standardized it, IIRC. PMC might make a lot of sense.
> If you want to browse for high-quality miniature connectors that
> offer controlled-impedance differential pairs, try the first few sections
> of Samtec catalog. I've used their stuff in quite a few designs. It's
> relatively expensive, but top-notch, and they ship extremely fast, even for
> items they don't have assembled in stock.
>
>
>
On further thought, one argument for PMC is that it lets the
customer plug in any of a large assortment of off-the-shelf PMC modules to
build up a system. It's also much easier to design a custom PMC module than
a whole OGD base board.
One difficulty is that PMC requires the connectors to be at specific
locations so that the piggyback module's connectors will align properly with
the chassis' rear panel. This might create parts placement difficulties on
the OGD board. Also, do we know whether it's even possible to mount a PMC
module on a PCI board, and have its external connectors fit properly in the
rear panel holes of a PC chassis? Somebody would have to read the PMC specs
to make that determination. I'd think that it would at least require a
double-width rear panel on the PCI board.
So, this leads me to think that PMC sockets would be a factory
option, rather than a default feature. If there are alignment holes for the
PMC sockets, though, they should be field-installable for anybody who's
handy with a solder iron. (Or maybe it would ship with the sockets soldered
in place, and a spare rear panel for field conversion to double-width PMC
form.)
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