Darrell -
On Fri, Nov 11, 2005 at 06:32:47PM -0500, Darrell Harmon wrote:
> > [re: http://recycle.lbl.gov/~ldoolitt/ft256/]
> Nice job routing out all the signals.
Thanks!
> However, you
> still have to deal with the VCCO. That could be a mess if you
> have too many IO voltages.
Nobody in his/her right mind would use eight different voltages.
OTOH, I haven't divided up the I/O yet into 2.5V and 3.3V segments,
so I kept the banks separate so far.
> I did use 20 0402 caps, but I
> suspect that was unnecessary. They fit much better than 0603s
> so I could get them closer, but they are hard to solder.
I can see [from http://dlharmon.com/dspcard/dspcard-art.pdf] they
really help for VCCAUX. I have worked my way down from 1206 to
0805 to 0603. At this point 805 are "easy" and 0603 are "OK" for
my handwork/testing/repair. 0402 is still too scary.
Unlike previous generations of Xilinx chips, I couldn't find any
recommendations/app notes for decoupling of the Spartan3. So I
don't know how many decoupling caps to attempt, beyond the obvious
"one per power pin".
Thanks for your comments!
- Larry
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