[Color Computer] Re: [Coco] Hidden 256-color mode

[James Diffendaffer]

I thought enabling the 256 color mode was difficult because they had
run out of physical pins on the chip rather than to hide the mode from
Tandy.  Not releasing the info was because of Tandy for sure.

Whether or not the 256 color mode is still in the chip probably
depends on a lot of things.  I think there are a lot of reasons that
support leaving in the mode.

We know the prototype would have had to support the mode in order for
an engineer to test it.

Unless they reworked the prototype to test it without the mode they
would probably leave it in to avoid potential problems with the die.

The mode was difficult to access anyway so removing it wasn't required
unless there was some incentive to do so.  Changing a design or die
back then wasn't as easy as it is today.

Given the diagram for the chip I don't think they would save a lot of
die space by removing it so there wasn't major financial incentive to
rework the die.

And with engineers being engineers I'd say they might leave it in no
matter what Tandy said.  It's not like Tandy was going to test it to
see if the mode had been removed.  They probably didn't even know how
to turn it on in the first place.

As for how the mode works/worked...
It would be great if it were a user configurable palette but it would
require additional hardware to store the palette and handle setup. 
That increases complexity and size of the die so I don't think it's
likely.

However if each byte had the color info built in then the hardware
just bypasses some of the existing hardware when in the 256 color mode
and passes on the info dirrectly.  That certainly looks like a "hey,
we could throw in a 256 color mode by doing this" type of hack and
engineer might come up with.  It reminds me of the half bright mode on
the Amiga.  It was there but only a handfull of programs used it.

The possibilies I see are:
yyyyyrgb - 8 colors with 32 levels of intensity
yyrrggbb - 64 colors with 4 levels of intensity

I think the last one makes the most sense and would be most usefull
for games.  It still works within the 64 color palette of the CoCo but
with intensity.





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