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Apple brand IIGS Memory Expansion Bank Mapping

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#1 Bloodnose OFFLINE  


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  • Location:Richmond, RI

Posted Sat Apr 8, 2017 5:03 PM

I have a fully populated (1MB) Apple Computer / Apple IIGS Memory Expansion card.


Testing with MegaMemoryTester reported,

Bad memory word detected,

$080000 R $0002 E $0000

This result would not occur on every test iteration, but would occur more often than not.
I could not find a reference online to which chips belong to bank $08, so I tried relocating chips to see if I could narrow it down.
I reversed all socketed chips.
(Chips UA1 through UA8 are soldered)
That is, UA9 was swapped with UB16, UA10 with UB15, etc.
Now MegaMemoryTester reports,

Bad memory word detected,

$100000 R $0040 E $0000

So, reasonably, the bad chip was relocated from bank $08 to bank $10.
There are 32 chips on this board.
Bank $11 (decimal 17) *might* be UB15,UB16, or it could be UB1,UB2.
Assuming UA1,UA2 is the beginning bank of expanded memory, which MegaMemoryTester starts with ($02), then bank $10 should be UB13,UB14 or UB1,UB2.
But I've swapped pair of chips all the way from UA9,UA10 through UB15,UB16, and I will always receive a bad memory at $100000.
Is there any logic to bank mapping?
Or are memory banks interlaced somehow through these two rows of 32 chips?


#2 Bloodnose OFFLINE  


    Star Raider

  • Topic Starter
  • 51 posts
  • Location:Richmond, RI

Posted Tue Apr 11, 2017 6:47 PM

I have now tested the same memory expansion card in a ROM 3.  The previous test was done in a ROM 01.


Testing starts at bank $10 on a ROM 3 rather than $02 on a ROM 01.


The same bank location is marked bad on the ROM 3, $100000.


There is a slight difference however.  The bad memory report occurred on the ROM 01 during the "Bit Test" of MegaMemoryTester.

On the ROM 3, it occurs on "Phase 2 Read" of $100000.  The "Bit Test" which starts at $100000 on the ROM 3 reports no error.


Should I now suspect the support chips instead of the DRAM chips?

Why would it have changed from $080000 to $100000 on the ROM 01 when I reversed the chips?


I will continue my research by moving these DRAM chips to a different Apple brand GS RAM Expansion card.

I will report my results.

Who knows, maybe someone will be interested in this.

Maybe someone knows how DRAM chips are mapped into banks.

I've got other working expansion cards to use, I'm just investigating this out of pure curiosity.

Also, rather than disposing these cards, I'd like to pass them on to someone who might want them in working order.

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