Re: VIC-II and luma levels

From: Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de>
Date: Fri, 13 Jan 2012 18:05:50 +0100
Message-ID: <4F10646E.9060902@laosinh.s.bawue.de>
On 01/13/2012 04:00 PM, Segher Boessenkool wrote:
>> I know there is a major difference in the PAL version of the VIC-II
>> between the 6569R1 and all later versions. The R1 is only able to do 5
>> luma levels (1-4-6-4-1 number of colors per level) for the 16 colors
>> while the later versions are able to do 9 luma levels
>> (1-2-2-2-2-2-2-2-1). Some demos look quite odd on the R1.
>
> The LUM signal has an external pullup; everything inside the VIC-II
> does pulldown only.

Yes... And that pullup is integrated into the RF modulator. Which makes 
removing the modulator to improve picture quality a pain.



> The newer chips supposedly are nine levels, just like PAL; but indeed,
> when did they change from five?

I found this picture today while trying to do some further research:

 
http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/656x-luminances.gif

 From this image is looks like they were still finetuning the resitor 
values after R3. Too bad the image doesn't contain values for the HMOS 
versions.

And here's some other information:

http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/656x-luminances.txt

Why do I always come up with the proper google terms some hours after 
sending a mail out? :)

  Gerrit


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