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ATARI 12MHz Portfolio - the fastest ATARI Portfolio in the world !


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Hi folks,


the standard upgrade from 4.9152 MHz to 6.144 MHz is well known and proven🙂.


But I wanted to shift a gear higher and try to go to the limits😎.


Here some first tests with an ATARI Portfolio HPC-006 with 12 MHz!


The graphic controller makes some problems, characters are not deleted or refreshed.

But basically the Portfolio can be started, accessed and operated. 

The CPU testtool also shows a fabulous 11,98MHz clock frequency😎.


But these are only the first tests, I'll give an update if there is further progress.






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Edited by andymanone
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On 3/16/2023 at 11:16 PM, Cyprian said:



what about a bit lower clock e.g. 9MHz?

Hi Cyprian,


yes, I immediately ordered a few more crystals to test with 6.144MHz, 8.000MHz, 9.216MHz and 12MHz each.

Strangely enough, the tests with lower frequencies failed, (8.000MHz, 9.216MHz) turned out badly.

The portfolio starts, but the display shows chaotic characters and halves the lines. Absolutely unreadable.


Than I ordered additional crystals with exactly twice the frequency of the standard clock (9,830400 MHz)
and then some with the double frequency of the (known) 6,144MHz mod's, so 12,288MHz.


Funnily enough, the test with 9.830400 MHz (standard clock x2) was just as bad as the others under 12 MHz,


BUT (!)


The test with the 12.288MHz was a little bit more successful😎!

There are again some characters that are not deleted, and there is always a wrong line break,
but if you execute the command "cls" once or twice in the prompt, the remaining characters are
deleted and the text is partially displayed normally.


The test tool then even shows 12.27MHz!


With the 12.288MHz crystal, the Pofo also behaves better than with the previous smooth 12'er.


But it can't start programs from the ROM cleanly, I assume that the access speed of the ROM's is

just too slow for the (almost 3 times) CPU speed 🙄.


Well, I'll continue a little bit, let's see what I can figure out...



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WhatsApp Image 2023-03-18 at 14.12.38.jpeg

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For stability, would possibly replacing the 80C88 with a higher rated one allow it to run stably? I don't know exactly how the video system works but it might be CPU driven being a monochrome DOS machine. There's the 10MHz OKI 80C88 which could be swapped on.

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