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

jdaggett at gate.net jdaggett at gate.net
Thu Jul 28 15:01:20 EDT 2005

On 27 Jul 2005 at 17:47, James Diffendaffer wrote:

To:             	ColorComputer at yahoogroups.com
From:           	"James Diffendaffer" <jdiffendaffer at yahoo.com>
Date sent:      	Wed, 27 Jul 2005 17:47:39 -0000
Subject:        	[Color Computer] Re: [Coco] Hidden 256-color mode
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> 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 it is a pin limitation or not would require inspection of the die itself. My best 
estimate is that the size of the die is not a limitation and that RS limited pin count 
for cost reasons. 

> 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.

Future model expansion without large scale of hardware change. Yes that is 

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

Prototype boards would have it and also features can be removed for cost reasons 
as wellas internal politics of a company. 
> Unless they reworked the prototype to test it without the mode they
> would probably leave it in to avoid potential problems with the die.
IF a feature is left out of the final product, it still can remain in the prototype board. 
>From some picture of the prototype, it does apear that a 256 byte rom is incorprated 
into the prototype board. 

> 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.

The mode can be there on the die but not wired up. While t his is not practical as 
die area is money. IN th is case probably upwards to $0.20 per part. 
> 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.
Beleive me if it were finacially beneficial that section would get removed. I suspect 
that the 87 GIME chip has that section removed if the 86 chip indeed did. 
> 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.
In software one can hide and leave easter eggs in and get away with it. In hardware 
that is not always true. 

> 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


first off this format will yield three colors and 32 levels of intensity. 
> yyrrggbb - 64 colors with 4 levels of intensity

I would think more like 


this yield 256 color combinations. 

> 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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