Re: Apple II VGA Video Generator Card Project

["Bryan Parkoff" <none@nospam.net>]

"Jorge Chamorro Bieling" <bieling@terra.es> wrote in message 
1hayiar.1guk4651d7lh1uN%bieling@terra.es">news:1hayiar.1guk4651d7lh1uN%bieling@terra.es...
>I was already thinking about modifying my videx to do that, and I may
> try to do it someday...
>
> ..but reading what you the people at csa2 are saying this week, I've
> seen that having a modified videx maybe a nice thing but is not *the
> solution*.
>
> So here is what I've been thinking about it this week.
> May it be the way to go ?
>
> "Apple II VGA Video Generator Card Project"
> <http://homepage.mac.com/jorgechamorro/a2things/index.html>
>
> What do you think ?
>
> Regards,
> -- 
> Jorge Chamorro Bieling

    I have read if I understand, but I want to give you my thought.  They 
claim to add incompatible video mode.  Do you mean to add new softswitch for 
VGA?  If it is the issue, I would suggest to have 256 colors at 320x200 
resolution.  Total bytes are 64,000.  You can divide it into 32,000.  Main 
memory will have 32,000 bytes and aux memory will have 32,000 bytes.  Both 
of them start at $2000 through $9D00.
    The problem is that it takes too much memory which it does not have 
enough memory for software to run.  It may have approximately 16K available 
in both main and aux memory.  Then 16K in high RAM ($D000-$FFFF) are needed 
to bring total up to 60KB in both main/aux memory.
    I have been considering to use EGA instead of VGA.  It would be only 
32,000 bytes in aux memory from $2000 through $9D00..  It would be 16 colors 
at 320x200 resolution.  It gives enough memory in main memory for software 
(from $800 through $BFFF) to run while it begins to draw pixel by pixel in 
aux memory by transferring data from main memory to aux memory.
    It can be forth try unless we have to find other way to add a new 
softswitch to support video mode for EGA and VGA.  Apple II can't add new 
softswitches unless we should be able to modify softswitch logic on the 
motherboard.
    In other words, I understand that you may want to emulate NTSC into VGA 
using existing Apple II's video modes.
    Please provide what do you think?

Bryan Parkoff