Re: How does the apple2 RGB card work?

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

Bryan Parkoff wrote:
> "mdj" <mdj.mdj@gmail.com> wrote in message
> 1148960973.360856.166780@j55g2000cwa.googlegroups.com">news:1148960973.360856.166780@j55g2000cwa.googlegroups.com...
> > What am I, Google? ;-)
> >
> > http://bobsc5.home.comcast.net/aal/1986/aal8608.html#a6
> >
>
>     Thanks for the information.  Like I said earlier 160 Mode is on Mode 0.
> I think that 160 Mode is not true 640x200 because it has restricted to
> 560x192.  When you put low nibble in $2000, four pixels will be displayed in
> position 0 through 3 and high nibble displays only three pixels in position
> 4 through 6.  The fact is that it does read four bits in high nibble to
> select one of 16 colors, but it can't display 4 pixels.  It is what I refer
> shrinked from 8 pixels to 7 pixels each column.
>     I think that 160 Mode is misconcept so it should be referred to 160
> columns shrinked into 140 Mode.  What do you think?

It has been a long, long time since I've messed with the undocumented
modes. I'd imagine, though, that what it actually does in this case is
output 4 pixel wide colours in one memory bank and 3 pixel wide in the
other bank. This would give a 160x192 colour display over a 560x192
raster signal.

The mode isn't used by any piece of software outside of demo's as far
as I know. It's possible that the spreadsheet program VIP Professional
may have used it for graph displays. It's the only piece of software
I'm aware of the made use of some of Applied Engineerings more exotic
IIe extensions.

Basically, I think you'll find that VIDEO 7 needed to implement 2
decoders to do DHR in RGB, one for mono, one for colour. This basically
meant that implementing MIX was a piece of cake, just using a selector
to switch between decoders for each byte. It was probably then very
simple to add the 'bonus' modes with the available hardware, so they
did so.

>     Do AE RAMWorks III have optional RGB?  If yes, where should I start
> configuring it?

Sorry, I don't follow. There were three addon boards for the RamWorks
over the years to provide RGB output. Each allowed different sorts of
displays to be driven (Apple Digital, CGA, and Apple Analog). Each was
identical to the AppleColour RGB card in terms of functionality, ie.
the VIDEO7 RGB modes.

Matt