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FW: 2 layer PCI and meeting spec



All,

All students want to minimize the work required to ensure a working project.
To meet this goal, I'd design with four layers and decouple carefully. A
conservative approach is the fastest way to a working board. Debugging is
hard enough if you know you've followed the rules. Who wants to troubleshoot
inevitable issues on a two layer PCI board?

Jim Sather

-----Original Message-----
From: Tony Burch [mailto:tony@BurchED.com.au] 
Sent: Tuesday, March 26, 2002 5:03 PM
To: pci-sig@znyx.com
Subject: Re: 2 layer PCI and meeting spec


Hi,

Daniel makes a good point.

I don't know if it's possible, or likely,  that
a two layer PCI card is strictly PCI
compliant.  That is not to say that
they don't work.

Those two layer cards mentioned
are designed from the "ground-up",
or the "ASIC-up".  Most of the digital
logic on those cards is implemented
on a single ASIC, and the board connections
to the PCI edge connector are direct and short
(with the exception PCLK), and have no track
cross-overs.

I think alot can be learned from having
a close look at some of these cards.

If you are going to design something with
a 2 layer board, routing out your devices
will be an issue, and you won't be able
to use devices with BGA packages - quad
flat packs would probably be the only
option.

Seems like a minefield to design a PCI
compliant  card with a two layer board.
For a student project, I think go for it.
But for a commercial product,
it is definitely wise to use multi-layer,
until maybe you can put all of your
digital functionality into an ASIC or
gate array.

This is only my opinion, and I will
be interested to read comments from
others.

Best regards
Tony Burch
http://www.BurchED.com
Low cost FPGA boards, for System-On-Chip
prototyping and education

----- Original Message -----
From: "Daniel DeConinck" <daniel.deconinck@sympatico.ca>
To: <pci-sig@znyx.com>
Sent: Wednesday, 27 March 2002 8:50
Subject: 2 layer PCI and meeting spec


Hello,

Observation re 2 layer PCI:

I can name two common devices that are sold in the tens if not hundreds of
millions of units and that are 2 layer PCI boards. These would be ethernet
cards and sound cards. These cards sell for around $20. They need to be made
dirt cheap and they need to work on a very very high percentage of
motherboards to avoid a bankruptcy inducing support nightmare. And they must
work in conjunction with whatever else is plugged into the host PCI bus.

So my conclusion is, that in the real world you can often ( and many do )
get away with it.

I am not qualified to answer the question from an engineering perspective
but I would like to hear what others have to say.

Sincerely
Daniel DeConinck
www.PixelSmart.com
TEL: 416-248-4473