QBZJ@CORNELLA.BITNET (10/13/86)
Could someone give me some ideas about what to try to salvage my memory
upgrade? I have a 520 with the rev C board. I followed the instructions
for the upgrade carefully and am reasonably confident that I have not made
any mistakes. I removed the capacitors, piggybacked the new ram chips,
reinstalledthe capacitors, ran the new cas low and cas high buses and the
new ras bus, installed the 68 ohm resstors in series with those lines to
the mmu. The next part of the upgrade called for the cutting of the old
cas and ras lines to the original memory bank and then remaking the
contacts with a 68 ohm resistor in series. On the rev C board, atari has
already cut these traces and installed 68 ohm resistors on the cas lines
at the ram chips. kkSo I just cut the ras line and added the 68 ohm resistor,
thankig atari for making my job a little easier. I checked all resistances
from the mmu to the appropriate bus and all looked great. When I rebooted
my 520 everything looked fine except the new memory was not there! So I
used basic to check things out. I have memory that I can write to from
$80000 to $9FFFF. All bits in high and low addresses work swell. From
$A0000 on up I get $48 and $80 in odd and even (or even and odd) addresses
So it appears that the computer is willing to read and write from the low
128k or the addition but not above that. All of the base 512k is there.
Could someone please send me some ideas such as how the mmu recognizes whether
the second bank is made out of 64k, 25k or 1M drams? Thanks very much.
peter lorraine
qbzj@cornella.bitnet