Re: How does the apple2 RGB card work?

["mdj" <mdj.mdj@gmail.com>]

Bryan Parkoff wrote:

>     I am not sure what I understand that you are referring $2000-$3FFF in
> aux memory for HGR (not DHGR).  Can you please explain little more?

This is the undocumented Mode 5 I referred to previously ...
Essentially it applies the same technique used to produce 40 column
colour text to the HIRES display. The main memory buffer is treated as
monochrome HIRES, and the auxiliary buffer is used for colour
information.

It would seem that the VIDEO7 crew after implementing mono DHR, then
colour DHR as seperate modes, realised that MIX was only an extra IC
away. The other modes are also very simply generated from the available
data stream.

There was an article on the undocumented mode in Apple Assembly Line,
which is how I learned of it's existence. The AppleColour RGB demo disk
also includes a demonstration for it, but it's use other than emulating
monochrome HIRES correctly is pretty limited, IMHO

It's worth preserving even just to achieve that, however.

Matt