Another Zip story, episode 2...

[o9938156@wsuaix.csc.wsu.edu (mark lyon)]

Well, I have been playing with the 14MHz 65816 again for the
past week or so.  I have tried Jawaid Bazyar's suggestion
of putting some capacitors across the power pins of the
cache rams.  Here is what I have discovered...

- Putting capacitors across the power pins (I just piggybacked
the small SMD capacitors that are already there) had no noticable
effect (@ 8MHz).  I tried up to 120uF electrolytics, so size wa
 not the problem.  I also put .1uF caps across the 74ACxx chips.

- When I replaced the shield (aluminum foil) around the board,
it had very little effect, as opposed to a large effect w/o
the caps (@13.75MHz).

Conclusion:  It was the increased capacitance caused by the
shield that helped.  With the caps, the foil was farther away
from the traces than without, so the capacitance was less.
The noise also seems to be on the I/O or address lines, rather
than the power lines, because the capacitors on the power
lines had no effect.  Perhaps the traces are too close together?

I then tried just a single sheet of aluminum foil, attached to
the back of the board with double-stick tape.  This gave the
best results yet (fewest crashes), but the computer would
still crash after a while.  Other than that, I don't know
how to increase the capacitance further, without finding
the offending lines & attaching capacitors to them.  If
I get time, I will try to do that.  In the meantime, I
will give up and order some low power SRAM's, but even
with low power rams, this may help to run a little faster.

Mark Marr-Lyon
o9938156@wsuaix.csc.wsu.edu