Universal Adapters

[Irv Negrin <IDN@nms.com>]

Hi fellow PCI designers:

With 3.3V parts popping up everywhere, I'm considering targetting my
new design to be a Universal card.  I just want to clarify what is required
to make sure I'm not missing anything.  Anybody who is in the know
please confirm.

1.  You require a PCI bridge capable of driving 3.3V logic without
damaging any devices on the bus.  This is done typically by using a 3.3V
device with 5V tolerant I/O or a 5V device that can be configured to drive
3.3V when it's PCI bus VDD pins are tied to 3.3V.

2.  Connect the 5 VIO pins (from the universal card pinnout) to the PCI
bus VDD pins on the bridge.

3.  Here's the big concern:  Use both 5V and 3.3V supplies to power the
various devices on the card.  With more and more parts requiring 3.3V, it
is getting more difficult to generate it on-board from the 5V.  The question
is how compliant have motherboard manufacturers been in supporting
the 3.3V requirement?  Since Pentium 90 and now ATX, I have to imagine
most new products are compliant.

Thanks for taking the time

Irv
Nova Microsonics
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