Path: utzoo!attcan!uunet!cs.utexas.edu!samsung!munnari.oz.au!uniwa!wacsvax!cutmcvax!mestona
From: mestona@cutmcvax.OZ (meston anthony)
Newsgroups: comp.sys.amiga.hardware
Subject: old A2000 MMU/CPU memory board
Keywords: Help!!!!
Message-ID: <145@cutmcvax.OZ>
Date: 9 Jun 90 02:14:22 GMT
Reply-To: mestona@cutmcvax.oz (meston anthony)
Organization: Curtin University of Technology, Maths & Comp Sc
Lines: 54

I have an _OLD_ A2000 (you know, not the B2000) that has 512k chip on the main
mother board. (sob..) The machine has a memory board in the CPU slot with 512k
soldered, and sockets for another 512k AND.... FIVE JUMPERS... I found some
memory and put it in.  The only way that the computer would count 1 meg of
$C00000 memory was by swapping jumpers.  Not good.  This works fine for
everything _EXCEPT_ that a keyboard reset causes RAD: to suicide. Nothing else
in the $C00000 memory seems to be touched (ie guardian..) but the RAD: gives
Read/Write Errors (Grr..). When I examine RAD with a disk editor, there is a
single bit set near the start of some sectors causing a checksum error.
This only happens after a hard reset. A software reset such as issuing the reset
intruction or post-crash reset doesn't cause this. My guess is that the Board 
stops refreshing the ram during the reset which causing bit changes! (but why
only RAD: and not other kicktags???) Any help would be appreciated!

Next Question:
What are all the jumpers for?? A diagram: ( : means open, O means closed)
before (as shipped):   12345
                       :OOO: (component side up, edge conn down V )

after (my guess):      12345
                       :O::O

Apart from the reset problems, this seems to work.... (but I still want to know
what I have done..)

Final question:
At a local developers meeting, One of the people said that this board is
supposed to be able to overlay the kickstart roms with ram??? yes? no?
If this is possible, this would be MOST USEFUL!!!
From my experiments, this seems likely, because in the A2000 (note: _A_) the
custom chip registers are mapped over $C00000-$DFFFFF and this board overlays
the mapping. (ie writeing to $D00180 is the same as $DFF180 (or $C00180 with the
board out..)) It seems logical that overlaying the rom would be done the same
way. (on the A2000, *OVR can override anything..(I Think..))  But how are the
^*%%&$ing jumpers set up for this??? :-)

By the way, the developer support in Australia is terrible. That is if you can
even get to be registered!! An example: One person over here has written a
laser projection package, and all driver software.  You can paint pictures
like dpaint III and use cell animation and project it onto anything from
walls to clouds in the sky. He was not able to get developer status when he
needed it and still can't.  With support for the amiga in Australia like this,
it is no wonder the ST is starting to make a comeback over here.....

Ok, enough of my whining! :-)

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