Re: Apple II VGA video card and the IIgs

[bieling@terra.es (Jorge Chamorro Bieling)]

David Wilson <mcs6502@gmail.com> wrote:

> Jorge Chamorro Bieling wrote:
> > <aiiadict@gmail.com> wrote:
> >
> > > >Is there IIgs-specific slot in the IIgs that is different from the Apple
> > > >II slots ?
> 
> Slot 3 in the ROM01 IIgs and Slots 1-6 in the ROM03 has M2B0 on pin 35
> and both have /M2SEL on pin 39 in slots 1-6. These allow a card to
> detect reads/writes from/to the Mega II RAM and which bank is being
> accessed.

Yes !!!, that is was I was looking for :

"The Apple Video Overlay card uses M2B0 to detect writes to main and
auxiliary RAM so that it can capture writes to the Apple IIGS video
display buffers into its on-card display buffer. M2B0 is designed for
this sort of thing and isn't of much use in most other applications.
Note that M2B0 is only available on slot 3."

<http://web.pdx.edu/~heiss/technotes/iigs/tn.iigs.068.html>

-- 
Jorge Chamorro Bieling