Re: IIGS memory error

[dempson@actrix.gen.nz (David Empson)]

ground.ecn AppleII Librarian <apple2pd@garp3.icaen.uiowa.edu> wrote:

> I haven't determined memory mapping for the 1Mb Apple expansion card yet.
> Board with 256K shows memory to $12000 ???, with 512K memory goes to $16000
> ???.  So I think MB = $80000, plus $40000 per 256K.  (I am trusting my memory
> here so I may be wrong. In fact, this can't be right).

$10000 is 64K, so 256K is $40000 (4 times 64K) and 1 MB is $100000 (16
times 64K).

You didn't do your hex arithmetic right.  Assuming the numbers you saw
were actually $120000 and $140000 (one more zero in each case), then
$120000 - $40000 = $E0000 (not $80000).

It sounds like whatever displayed these numbers ($120000 and $160000) is
not including the first two banks on the motherboard.  Were you looking
at the "maximum" figure for the RAM disk, perhaps?  (They would be 896K
for a bare ROM 3, 1152K for 256K memory expansion, and 1408K for 512K
memory expansion.)

> Anyway, I did all my testing with 512K memory.  First I removed all 24
> chips, then used groups of 8 until I had a group of 8 that worked.  Then I
> swapped in four chips at a time to find a good groups of 4.  Then 2 at a
> time from the bad groups of 4 to get good groups of 2.  Finally I had two
> groups of bad 2 chips.  Then I found the two bad and two good chips.
> I used the memoryCL pgm from Claris AWGS for memory tests.

Good batting, thinkman!

-- 
David Empson
dempson@actrix.gen.nz