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Coleco Adam Diagnostic ROM on a MegaCart (256kb)


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Hey guys,


I am currently repairing a defective Coleco Adam (Expansion Module 3).

I have a MegaCart with a 256kb Flash Rom, with which I could already use Zaxxon Super Game (128kb ROM) and the Adam Final Test ROM (16kb).


But I would like to use the Coleco Adam Diagnostic ROM (32kb).

Is there a way to get this ROM to run on the MegaCart?

I know that bank switching allows the MegaCart to access a fixed and a flexible 16kb area.

I therefore split the 32kb ROM image into two 16kb pieces and then copied part 2 15 times in a row and part 1 at the end to fill the 256kb.

But unfortunately this did not work.


Is there any way to get a 32kb ROM image to run on the MegaCart?

Perhaps by reprogramming the GAL?


Thank you very much for your support.


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No idea but you might want to try Gamma Debug as it provides much more detail on individual chips rather than the simple PASS/FAIL messages provided by ADAM Diagnostic which aren’t much help in figuring out what any system issue might be.


IIRC the Gamma Debug rom image is only 8K.

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Thanks for the info. I'll try the Gamma Debug.


I thought that the Gamma Debug does only check the ColecoVision hardware and the Adam RAMs, but no other checks on the Adam and hoped that I could get further information from the Adam Diagnostic.


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I think you are correct and the ADAM Final Test is another good one to use that provides a little more detail than ADAM Diagnostic.


if you can’t figure out how to get ADAM Diagnostic working on a MegaCart PCB, you could use a standard Homebrew 32K Cart PCB or use the version of it that is available on disk image that is in The ADAM Archive if you can transfer it back to an ADAM disk or have an SD Drive solution. Check out the disk images named ADAM Utilities.

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On 2/16/2024 at 12:17 AM, Pegamode said:

I guess this one should work, but I already have the MegaCart and hoped that there is a way to get a 32kb ROM image run on this one, too.

I searched for your image file, and NIAD already had posted it

However, the image file posted included a 256-byte header to run it from somewhere (probably CP/M).


I removed the 256-byte header as I noticed a ROM header just ahead, and I was baffled to see CoolCV couldn't run it, then I discovered the bank-switching port for ADAM covers $60-$7f and CoolCV only detected $7f, so I patched all the OUT ($60),a to OUT ($7F),a and guess what? It now works with CoolCV, although of course throws errors about ADAM hardware not found.


Please test this, I hope it helps you.





adamdiag_original.rom adamdiag_port_0x7f_coolcv.rom

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    IM      1
    LD      SP, $73B9
    LD      A, 9
    OUT     ($60), A    <--------
    LD      ($7FF0), A   <-------- load into an ADAM specific RAM which would be remapped on a Colecovision and failing being the CV ram ends at $73FF
    LD      IX, $38
    LD      (IX+0), $C3
    LD      DE, $8054
    LD      (IX+1), E
    LD      (IX+2), D
    LD      IX, $66
    LD      (IX+0), $ED
    LD      (IX+1), $45
    LD      A, $80
    OUT     ($FF), A
    LD      A, 7
    OUT     ($FF), A
    LD      A, $A0
    OUT     ($FF), A
    LD      A, $E
    OUT     (0FFH), A
    LD      A, $C0
    OUT     ($FF), A
    LD      A, $1C
    OUT     ($FF), A
    LD      A, $E5
    OUT     ($FF), A
    LD      A, $9F
    OUT     ($FF), A
    LD      A, $BF
    OUT     ($FF), A
    LD      A, $DF
    OUT     ($FF), A
    LD      A, $FF
    OUT     ($FF), A
    LD      HL, 0
    LD      DE, $4000
    LD      A, 0
    CALL    $9EAA
    JP      $80BB









         ld      hl, $8000
         ld      de, $200
         ld      bc, $7D00

         jp      $1328


It also transfers the binary data down to $200 before jumping to $1328
At that point the ram references are no longer $8000 and above unless trying to deal with ADAM specific functions.


Edited by Captain Cozmos
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