RE: 8088 and 610 saga continues...

From: Baltissen, GJPAA (Ruud) <>
Date: Thu, 27 Jan 2011 07:55:20 +0100
Message-ID: <>
Hallo allemaal,

> If the data on the lines does not go back to zero fast enough,
> it could appear as refresh data.

A normal refresh would NEVER change the data IMHO. If during a refresh
CAS is enabled as well, and according the right timing, then it isn't a
refresh anymore but a data access. But even that doesn't have to be
harmfull as well. A data access can only be destructive if the WE
(write) line has been activated as well. And if it is a data access,
only one address is involved. Which isn't according the facts :(

Hmmm, just struck my mind: during a normal refresh WE is always (H)
AFAIK. What happens if WE is accidently enabled during a refresh? Can
that be tested in some way? 

A second thought trail: why $21 and $A1 only ??? The only thing that
comes to my mind is that we find port B of the 6525 at address $21 of
the I/O part of the 8088. If a write to I/O $21 accidently triggers the
RAS line in one or another way, short circuit for example, you have
found your trouble shooter. A real refresh would only read port B which
wouldn't do any harm and therefore would go unnoticed. The only problem
I have with this idea: it would mean an error on the 8088 board and that
would mean that the problem should have shown up on the 720 as well. But
just in case...

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