Re: IIgs RGB to VGA continued

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

--
Making computers fun again
See the new AltairPC
http://www.brielcomputers.com

"Michael J. Mahon" <mjmahon@xxxxxxx> wrote in message
news:DNedneB4rYeW8m_ZnZ2dnUVZ_tudnZ2d@xxxxxxxxxxxxxx
jsnospam@xxxxxxxxxxx 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
tool--and it's seriously underused."


.

Relevant Pages

  • positive Craigslist story (from one perspective)
    ... looking for, listed at $450 with a small, low-res photo displayed... ... I arrive on Sun and can tell in 15 sec that this machine is a sweet ... seller is a mid 50ish guy who tells me he just divorced and is packing ... the lock open in under 1 min. ...
    (rec.games.pinball)
  • Re: Canal de Garonne - Agen
    ... I followed the Garonne on Google Maps downstream (i.e. towards the ... aqueduct) from the the projection of the line of the branch from Le ... Passage lock to the river bank for a long way, ... the downstream end of the cut that might be what the guy in the photo ...
    (uk.rec.waterways)
  • Re: Using Text Boxes in Word 2002
    ... I've been able to lock the text boxes together; ... If I select the photo first, and then select a text box, ... Q2 You can 'lock' drawing objects together by selecting them all (click on ...
    (microsoft.public.word.newusers)
  • Re: positive Craigslist story (from one perspective)
    ... the local pinball guys I keep in touch with emails me that a machine ... looking for, listed at $450 with a small, low-res photo displayed... ... seller is a mid 50ish guy who tells me he just divorced and is packing ... luck and then decided to try and pick the backbox door lock to access ...
    (rec.games.pinball)
  • Re: positive Craigslist story (from one perspective)
    ... the local pinball guys I keep in touch with emails me that a machine ... looking for, listed at $450 with a small, low-res photo displayed... ... seller is a mid 50ish guy who tells me he just divorced and is packing ... luck and then decided to try and pick the backbox door lock to access ...
    (rec.games.pinball)