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

[MdntTrain <js@cimmeri.com>]

On Apr 9, 1:55 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
> MdntTrain wrote:
> > On Apr 4, 5:02 pm, ferd...@gmx.de wrote:
>
> >>I've been working on a board to double each line of the Apple //e's
> >>video output so that it can be viewed on a normal VGA monitor.  My
> >>goal was the perfect picture quality. To yield it, I sampled the Apple
> >>video signal with the original Apple clock, stored it in RAM and
> >>displayed each line twice with double speed. This works so far (except
> >>for one timing problem that can be fixed by touching the correct
> >>line... this is going to be fixed) and produces an extremely crisp
> >>picture. Especially the 80-col mode is way better readable because the
> >>lines aren't that far apart as on a monochrome monitor.
> >>So far, so good. Now the problem starts: color. The signal needs to be
> >>converted to RGB somehow.
> >>I tried:
>
> >>1. Latch the video signal 4 times at different phases to  COLOR
> >>REFERENCE. (7M rising, 14M falling with 7M high, 7M falling, 14M
> >>falling with 7M low - note that COLOR REFERENCE becomes 7MHz after the
> >>conversion). These 4 signal are mixed to form the 3 colors. This
> >>method gives exact reproduction of the 15 LORES colors (I designed it
> >>to do so) but blurs the picture in HIRES.
>
> >>2. decode the color as above, but gate it with the monochrome signal,
> >>so that a green horizontal line actually becomes a dotted line. With
> >>some displays this looks really nice, but it sometimes produces ugly
> >>color fringes on white areas.
>
> >>The Apple //e's PAL encodes uses a circuit with a quad D-FF, but I
> >>don't know how it is wired.
> >>So I'm looking for the schematic of the //e's PAL encoder or the PAL
> >>color card for the ][.
>
> >>BTW: I'm missing both the Eurapple jumpers and the 14M/Graphics time
> >>signals on Slot 7 in the Apple //e PAL. I had to jumper them directly
> >>from the main board.
>
> >>Ferdinand Meyer-Hermann
>
> >   Just curious, is there any way to easily get the separate Y + C out
> > of a II?   Or are Y+C somehow generated as one?   I've yet to examine
> > this... but there are a variety of very good svideo->vga converters
> > already available used, inexpensively... a route I might prefer to go
> > as I own a few.
>
> Y and C are generated as a single signal, in the sense that only Y
> is generated, but with frequency components that will be detected by
> an NTSC monitor as chroma.  Separating them would have to be done
> as is is done in a monitor.
>
> -michael
>
> NadaPong: Network game demo for Apple II computers!
> Home page:  http://members.aol.com/MJMahon/
>
> "The wastebasket is our most important design
> tool--and it's seriously underused."- Hide quoted text -
>
> - Show quoted text -

   So the color is an artifact of some Y manipulation.  Weird.  Where
(or in what book) is a good description of this process?

  JS