Re: Disabling memory refresh in UltiMax mode Re: 6510 handling of $00 and $01 registers

From: Gerrit Heitsch <>
Date: Mon, 12 Dec 2011 17:06:20 +0100
Message-ID: <>
On 12/11/2011 10:08 PM, Spiro Trikaliotis wrote:
> Hello,
> * On Sun, Dec 11, 2011 at 09:04:07PM +0100 Gerrit Heitsch wrote:
>> On 12/11/2011 08:28 PM, Spiro Trikaliotis wrote:
>>> Hello Gerrit,
>>> * On Sat, Dec 10, 2011 at 09:14:03PM +0100 Gerrit Heitsch wrote:
>>>> On 12/10/2011 08:51 PM, Segher Boessenkool wrote:
>>>> I don't plan on using the 6569R1 regularly. But it's nice to have a
>>>> really old C64 (includes real PLA and -02 Kernal ROM) handy when
>>>> checking software compatibility. The RAM test I use crashes on the
>>>> -02 ROM, plug in a -03 ROM and it works.
>>> Why does it crash on a -02 ROM? I mean, the differences between -02 and
>>> -03 are very small.
>> I asked myself the same thing but didn't see a reason to investigate
>> in detail yet. The problem was reproducable though.
> Looking into the code, it is obvious: The code writes directly into Video
> RAM ($0400-$07FF), but never writes the color RAM ($D800-$DBFF). As the
> -02 ROM initializes the Color RAM to background color, you do not see
> the output.

Ah, OK, that explains things. Still means the program is not usable with 
a -02 Kernel ROM unless one thinks about the workaround before running it.

> BTW: The test is extremely simply and would not find many erroneous RAM
> chips, anyway.

So far the only defective RAM I had in these old systems was either 
stuck bits (very often the MT4264) or a complete core meltdown (system 
doesn't start up at all, defective chip gets very hot very fast)

So it's better than nothing. Always open for suggestions for a better 
test program though.


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Received on 2011-12-12 17:00:25

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