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Discussion Groups | FPGA-CPU | Re: Re: why FPGA?

This list is for discussion of the design and implementation of field-programmable gate array based processors and integrated systems. It is also for discussion and community support of the XSOC Project (see http://www.fpgacpu.org/xsoc).

Re: Re: why FPGA? - Jeff Brower - Jan 15 20:31:00 2005


Austin-

> You're welcome. Keep the trace length between the switches and the IC the
> shortest you can, and choose your switches wisely ;-) If you are pinning
> for an FPGA, make sure your FPGA pinout optimizes the routing...and also I'd
> suggest routing on the outer layers only (minimizing vias, such that you
> have none on the top layer, and only one to get to the bottom layer) and
> making sure you watch your trace characteristic impedance (which for PCI is
> 60-100 ohms...and get a copy of the PCI spec and look over the routing
> section for trace lengths etc.), which means you (or your PCB fabricator)
> have to calculate the trace widths, and make sure the PCB manufacturer knows
> what they are when you order the boards, in fact, I'd suggest asking them to
> work up a stack-up for you prior to PCB layout.
>
> Please feel free to ask me questions with regards to the PCI aspect of this
> if you have any.

What do you think about this one:

http://www.fairchildsemi.com/ds/FS/FSTD32211.pdf

That does most of the work in 16 x 5.5 mm. 48 bits is enough if I use the series R
method on slow signals, for example PME, CLKRUN, and RST. Does that sound at least
close to being legit?

> P.S. BTW, are you making a 5V only, or a "universal" card (3.3V and 5V)? If
> a universal card, there are other issues you may want to be aware of.

Normally it's supposed to be a 3.3V only card. There are some times though when it
has to drop into a 5V desktop PC environment. Grrr.

-Jeff





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