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Folks Or should I say “Motherboard Woes”. Cecil, Bill, Steve and I had a pretty long Teamspeak session
last Saturday discussing buss speed. What speeds CAN we put on our buss? None of us really knew! Cecil knew a lot about LVDS and
twisted pair, but we don’t have a twisted pair or coax buss! In fact we
tried to figure a way to get it into our tiny, cramped, custom designed
enclosure, which prompted my departure from the enclosure, buss connectors,
etc. However, the question remains! How DO we design our buss to
go the 133 mhz PCI standard or increasing speeds in the later PCI standards. (800
mhz and beyond?) Can we even go 24 mhz to the FPGA, divide by 2 and send it
back to the Janus? My thought was to try to ‘copy’ the PCI standards
(Not the connector, just the board spec for the standard). I found again, as I
knew before, PCI standards group is a private industry culb with a high price
to join. When you get right down to finding out more than the buss labels,
there ain’t much but general info. If you take a look at a mother board
or even a riser you sure can’t see the innards! There ain’t no
schematics ANYWHERE I can find! I did find some info in a pdf from a PCI Bridge Chip
manufacturer, on how to design with their chip which yielded some light on the
board design for 133 mhz. I didn’t have time to read all the stuff and it was a
bit beyond me, however I did see one highlight as to how the PCI buss needs to
be in order to support high speed design. The clocks and other “Critical signals” go on
the top surface of the board. This is followed by a groundplane layer. Followed by the Power supplies layer Followed by the bottom “Signal” layer (which I
took to mean slow speed stuff). That was pretty ‘sketchy’ but it was the
description and perhaps a start. Is this doable for our MB? I would hate to design and produce a motherboard which
couldn’t even pass I2C stuff without causing noise everywhere else. This
needs to be versatile and QUIET. Any suggestions as to where to go with a quiet, high speed
MB design? Thanks Eric |