mdj wrote:
> On Nov 14, 6:50 am, "Michael J. Mahon"  wrote:
>> mdj wrote:
>>> 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.
>> Ah, yes--"backward compatibility" for the new software,
and simpler
>> than providing a scheme for software to detect the card's presence
>> (or absence).  Just what I would have done in the circumstance.  ;-)
> 
> It's an excellent design. I never did figure out if the IIc versions
> could interpolate the switching protocol somehow from the expansion
> connector. One of these days I'll have to grab such an adapter and
> test it out.
> 
> I always thought it a shame that the IIgs didn't support this. It did
> provide a way to do colour/mono selection, but it was rare that I
> found a mono-dhr application that didn't require me to activate
> monochrome in the control panel.

Apple had a very mixed record on "adopting" _de facto_ standards created
by third parties, even when they were well thought out.

The ThunderClock comes to mind as a winner, though its lack of a "year"
register led to the 5/6-year rollover in the year table in ProDOS--not
a very clean clock, actually.

The Zip Chip was adopted in the IIc+, though it is so invisible to
software that only its control was an extension to the architecture,
and even then, it wasn't carried forward to the IIgs.

The "standard" of slot 3 for an 80-column card was, I think, a third-
party creation.

It always struck me as peculiar that Apple never directly supported
the usual AUX slot bank-switching memory expansion scheme, even though
it was "market standardized" by AE and adopted by many others, with
pretty wide software support.

On balance, Apple acted pretty "proprietary" when it came to others
extending the _de facto_ Apple II architecture, even though they
actively encouraged third party extensions...

-michael

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