Re: RGB card

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

On Nov 13, 10:19 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
> Michael J. Mahon wrote:
> > Bill Garber wrote:
>
> >> "Jerry" <awande...@yahoo.ca> wrote in message
> >>m363mt5zna.fsf@yahoo.ca">news:m363mt5zna.fsf@yahoo.ca...
> >>> mojoehand <jg...@zianet.com> writes:
>
> >>>> Jerry Penner, I wanted to thank you for the information you emailed,
> >>>> but my reply bounced. It seems that Yahoo is being too agressive in
> >>>> its spam filtering.
>
> >>> Must be.  There was no message in my spam folder at all, which is the
> >>> usual case.
>
> >>> I would have put the patent document online, but I don't have a
> >>> web-site right now.
>
> >>> For others who are interested, the patent is US# 4,631,692, and can be
> >>> found at uspto.gov.
>
> >> I went there, and searched it, and the only info available was that it
> >> had expired on December 23, 1998. I couldn't actually find the Patent
> >> there.
>
> > Go to:  http://patft.uspto.gov/
>
> > and select Patent Number Search, then enter 4631692 and you'll see
> > the patent.  It describes a 4-bit shift register implementation,
> > where the shift register is clocked at 14.3MHz--the classic 16-color
> > implementation.
>
> I see Jerry made an equivalent suggestion.  ;-)
>
>  From the patent description, it seems that AN3 and /80COL need to be
> made available to the card to do mode selection.  (I wonder why the
> /DEVSEL space wasn't used for this function?)

The 80COL and AN3 softswitches are used in the IIe to enable Double
Hires and Lores modes. The Video7 RGB adapters established a protocol
for toggling these switches in certain sequences which enable
selection between DHR colour, mono, mixed, and '160' modes. There's
also a FG/BG mode that lets you do 280x192 single hires, and the AUX
page holds the FG/BG colours for each screen byte.

Using the protocol allows software to 'support' RGB cards by selecting
whatever mode is appropriate with completely benign results on non-RGB
equipped Apple II's.

Matt