Re: Q: RGBI (TTL) to VGA conversion - Experiences: MVC007 converter?

[Michael J. Mahon <mjmahon@aol.com>]

Sean Fahey <a2fan@hotmail.com> wrote:
> On Wednesday, March 27, 2013 9:29:39 AM UTC-5, Michael J. Mahon wrote:
>  
>> However, sweep frequency lock is only part of the problem. Video dot clock
>> lock is necessary to avoid the aliasing which mars so many scan converters
>> used with Apple II's. 
> 
> Clueless person here... and how is that best tapped? Something on a slot,
> or a pin on the VGC?

A suitable sampler would be able to recover the dot clock just from the
video signal, though some monitors require some fine manual adjustment even
with PC video to get the best results. 

In principle it should be quite easy with color Apple II graphics, since
the color burst is the same frequency (except for IIgs SHR). Text modes can
be tougher, but if the converter knows the approximate frequency, it should
be able to lock. 

Feeding the slot 7MHz signal to the right place in a converter capable of
14.3MHz lock should make it solid as a rock. 

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon