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

[ferdimh@gmx.de]

On 11 Apr., 19:12, sc...@alfter.DIESPAMMERSDIE.us (Scott Alfter)
wrote:
> In article <1c8828f0-6337-48fd-93b4-635edd509...@l64g2000hse.googlegroups.com>,
>
>  <ferd...@gmx.de> wrote:
> >Well, I think I said that. This is an expansion card to be plugged
> >into slot 7 of an Apple ][, ][+, or //e. The //gs is not supported
> >because of its completely different video subsystem. But if I have
> >time and a GS, I might consider designing a such a card for the GS. It
> >would be far more difficult to get a good picture then.
>
> For the IIGS, a scan doubler would suffice since its video output is already
> RGB.  If anything, I'd think it would be a fair bit simpler than what you're
> doing.
Well there are other problems. The ][ uses either 7 or 14 MHz dot
clock. So sampling with 14MHz will _ALWAYS_ produce a crisp display.
the //gs can use, 7,8,14 or 16 MHz dot clock. There is no longer a
clock that can be used all the time! Using a dot clock that doesn't
fit produces artifacts. To elliminate them, a low-pass filter is
added, blurring the picture. And the Apple //gs's output is an analog
video signal with 12 bit color depth. So one needs to handle 12 times
the data per clock cycle.
There would be no trouble with color decoding, that's right.

Ferdinand