Re: Apple ][ to VGA monitor adapter board - looking for best color decoding method

[ferdimh@gmx.de]

On 20 Apr., 19:19, MdntTrain <j...@cimmeri.com> wrote:
> On Apr 14, 12:45 pm, ferd...@gmx.de wrote:
>
> > This is a nice idea, but it won't work in the way my card works.
> > The 1-bit video stream of the ][ / //e is double-scanned, and the RGB
> > conversion is done afterwards. This saves an ADC, some sort of clock
> > regeneration, and lowers the data rate, so that normal RAM can be
> > used. It also simplifies the scanning counters, because they only have
> > to be 7 bits wide (912 pixels per line packed in 8-bit groups=114
> > bytes).
> > RAM size is not of any concern anymore.
>
> I'm not at a high enough tech level to understand what you just wrote,
> but I very much appreciate your attempt. :-)   I hope you've the time
> for a detailed "circuit description" in your VGA manual, as that would
> be a great vintage element in itself to have as well, as well as being
> a "good novel" for some of us nuts.    Manuals these days -- if you
> even get one -- are nearly all solid turd (I say "nearly" as I pray
> there are exceptions -- though I've not yet seen one).

I'm going to do that because you said that...
>
> > Compatibility with the //gs is another problem, because the GS uses 2
> > slightly different dot clocks. If the scan doubler works perfectly in
> > one mode, it won't in the other.
>
> So what about just having two clocks, with a switch to toggle them?
> Given the gains, I certainly wouldn't mind manually toggling modes as
> long as the switch was convenient.
>
> We (my friend Roy and I) encountered this problem in trying to adapt
> an Averlogix chip for doing low-cost IIgs RGB->VGA conversion.  We
> actually inserted it prior to the IIgs video D/A converters.. so that
> it would be D-D-A.  It worked great for the 7/14mhz modes, but we ran
> out of smarts on how to get it to synch to the 8/16mhz modes, and
> started to think about the filter method.  For best results, it seemed
> to require a rather complex active filter that we didn't have the
> experience and time to develop.
>
I consider doing that if you offer me a free GS ;-)
There should be a softswitch for the modes that can be examined by the
card. There is no real need for a hardware switch.
> That's true.. all my RGB monitors have Composite in.  However, YUV
> might be interesting.. especially to try with YUV-Digital DVI/HDMI
> converters.
This may be a thought.

Ferdinand Meyer-Hermann

PS: The server went down over the weekend, but is back up now. The
pictures can be viewed again.