Re: IIgs RGB to VGA continued

["Vince Briel" <vbriel@removethisspamcamcast.net>]

Michael, did you notice that it isn't on the b&w section on paint? I agree 
about trying different different dot clock lock if that is possible. I can't 
find my sheets on these IC's but I don't remember having that control.

J - What averlogic ic are you using? I was looking into that IC last year 
for the same thing but haven't had time to mess with it. Now I must rummage 
threw my files for them.

Vince

-- 
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"Michael J. Mahon" <mjmahon@aol.com> wrote in message 
DNedneB4rYeW8m_ZnZ2dnUVZ_tudnZ2d@comcast.com">news:DNedneB4rYeW8m_ZnZ2dnUVZ_tudnZ2d@comcast.com...
> jsnospam@cimmeri.com wrote:
>> Repost with all photo links.
>>
>> Hi, all.   I'd like feedback from those of you who might know what's
>> going on here in the following photos.   We've got a prototype VGA
>> converter going using some of the Averlogic chips.  All modes except
>> 620x200 are great, but I don't understand yet what's going on in
>> 640x200.
>>
>> All photos below are of a VGA screen, using converted RGB->VGA video
>> (no composite!).
>>
>>
>> First photo:
>> http://members.aol.com/mdnttrain/vga1.jpg
>> This photo shows GSOS bootup.  What are you seeing here?
>>
>> I'm seeing two things:
>>
>>   1) seems like every other vertical line is black.
>>
>>   2) seems like alternating vertical groups of lines are in color, and
>> not.  In the photo only (not when viewing), the groups that are in
>> color don't show the in-between blackness as much so you might have a
>> hard time seeing.
>>
>>
>> Second photo:
>> http://members.aol.com/mdnttrain/vga2.jpg
>> This photo shows the color bands quite well in the GSOS desktop colors
>> area.  But note that not every alternate line is black.. sometimes it's
>> a colored line.. as in the yellow/pink area.
>>
>>
>> Third photo:
>> http://members.aol.com/mdnttrain/vga3.jpg
>> Another desktop view
>>
>>
>> Fourth photo:
>> http://members.aol.com/mdnttrain/vga4.jpg
>> Booting into Platimum Paint in 320x200 mode, colors are solid and
>> perfect.
>>
>>
>> Fifth photo:
>> http://members.aol.com/mdnttrain/vga5.jpg
>> Same program, switching into 640x200 mode.. reveals all the same
>> desktop flaws.  Note again the yellow/pink alternating area is solid..
>> suggesting these alternating lines are deliberate and are "dithering."
>
> One comment:  since you are asking for comments about 640 pixel mode,
> and the raster is a fraction of the photo, it would be good to post
> photos that are *at least* 1280x960, if not more.  There is no
> "zooming in" to be done on the 640x480 photos posted.
>
>> One theory we have for the alternating black lines is that the
>> converter and monitor have too much bandwidth to dither.   A SVGA
>> monitor shows the dithering that the Apple uses to create colors
>> whereas an Apple RGB monitor does not have the bandwidth -- it simply
>> shows a solid color because it can't react fast enough to display it
>> (done on purpose).
>>
>> A low pass filter might lower the bandwidth of the SVGA
>> monitor/converter combo to equal that of those old monitors.
>
> Dithering is not supposed to occur on the monitor--it is supposed
> to occur in the viewer's eye.
>
> The problem that is occurring is not related to dithering except
> insofar as a dithered color is typically composed of alternating
> color pixels, and the response of the converter to this situation
> when the pixels change at a 14MHz rate is the problem.
>
> The banding is a "beat" between the IIgs dot clock and the converter's
> sampling clock.
>
>> However, the color banding problem persists.  Would this be some kind
>> of color reference signal lock problem?
>
> Not color reference (there isn't any in an RGB encoding), but dot clock
> lock.  Try to change the frequency of the sampling clock and see what
> happens.  I think you'll see why phase lock is needed.
>
>> Thanks in advance for any feedback.
>
> I hope you can get this working--a lot of people would love it!
>
> -michael
>
> New, faster SUDOKU v2.0 solver for Apple II's!
> Home page:  http://members.aol.com/MJMahon/
>
> "The wastebasket is our most important design
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