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Re: Another Zip story...
o9938156@wsuaix.csc.wsu.edu (mark lyon) writes:
>I've been playing with a 14 MHz 65816 too for several
>days now. I've not been entirely successful, however.
>After installing all necessary mods, the Zip would refuse
>to run at 13.75 MHz. The problem appeared to be with
>the cache RAM (15ns ISSI chips), as the Zip would run
>with the cache RAM set to 8K, but not anything higher.
>I have read about people having similar problems, but no
>solutions. What I tried was shielding the Zip from
>noise, which I've heard ROM 01's have plenty of.
My guess is actually power distribution problems and power/ground
noise caused by the Zip's 2-layer design. I have not yet proven this,
however.
Knowing that the Zip likes "low-power" SRAMs (but not standard SRAMs)
leads me to guess that it's a problem with noise on the power pins of
various parts on the board (caused by the SRAMs switching, of course).
Whoever made the decision to save a couple bucks on the Zip at the
cost of high-speed reliability ought to be shot. 4-layer does NOT
cost that much.
>So, I wrapped the Zip in several layers of aluminum foil
>(the thicker, the better) and connected the foil electrically
>to the metal case of the GS.
I'm not sure how effective a capacitor this is; I would guess
not very much at all, so this 'solution' may be only partially
related (or not at all) to my guess.
I recommend soldering fairly big caps (1uF perhaps?) onto the power/ground
pins of all the SRAM sockets, and standard 0.1uF caps onto the
TTL parts. You also might try running heavy-gauge wire from the
power pin on the GS slot connector to the SRAMs (same with the ground
pins, too).
All in all, the Zip's board layout is rather unimpressive.
--
Jawaid Bazyar | Like UNIX? Like your Apple IIGS? Then ask
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