Was it Ingraham, Andrew who wrote on Friday 06 September 2002 19:36:
> Declan,
>
> This all sounds familiar. Didn't you have a very similar problem a few
> years ago too? Something involving NMOS CPUs and pull-ups?
I was rooting at this a few years ago. Some of the issue was fixed by pulling
up one particular port on the cpu. That left me with some boartds with
HD6340s which worked, some boards with 6840s which didn't, and couldn't be
made to stand. I had stock, so it wasn't a great issue. but it never got
properly sorted
>
> I haven't touched NMOS in ages (if ever) so I'm certainly no expert ... but
> one might think that they all might have been designed with the same (TTL)
> thresholds. I suppose that would be wishful thinking.
AFAIK, the cmos thresholds are higher. The bus is clean enough, except for 2
databus lines which have slow rises. Pulling these high kills the board,
however. The Digital Signature Analyser has a funny impedance (Loads towards
1.4V) which distorts things, and generally it's a pain. Everything looks OK,
or better. Faults don't show. But the X@$�"! boards don't work!
--
Regards,
Declan Moriarty
Applied Researches - Ireland's Foremost Electronic Hardware Genius
A Slightly Serious(TM) Company
Experience is like a comb,
that Life gives you - AFTER all your hair has fallen out!
--
Author: Declan Moriarty
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