Re: Apple II VGA Video Generator Card Project

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

<aiiadict@gmail.com> wrote in message 
1140306684.239292.184900@o13g2000cwo.googlegroups.com">news:1140306684.239292.184900@o13g2000cwo.googlegroups.com...
> >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
>
> That is the idea..  New "softswitches" for **incompatible** video
> modes.
> Not a very useful thing (zero software available to take advantage of
> it)
> but it would be a fun project.
>
> in your example above, 1 pixel = 256 colors (eight bits, 1 byte)
>
> I'm going to get around to this project myself, eventually.  I'd like
> to hear of other resolutions / color schemes.
>
Hello,

    Yes, it is correct because VGA requires 64,000 bytes which each byte is 
256 colors while EGA requires only 32,000 bytes which each nibble is 16 
colors.  It is why I recommend EGA in aux memory.  I am concerned that high 
RAM ($D000 through $FFFF) in both main/aux memory will be set to read/write 
only when Applesoft BASIC ROM and Monitor / AutoStart ROM are not needed (or 
only 2-5 routines of monitor ROM are needed) otherwise you will have to 
write your own routines to support cold-warm reboot routine only.  No idea 
to deal with keyboard routine unless you need it.  It will be perfect for 
software with its own routines for cold-warm reboot and keyboard routines to 
run EGA and VGA memory when it does not need routines from Monitor ROM.
    Does it make sense to take more memory space?

Bryan Parkoff