[Coco] Re: Color Computer 3 prototype

[Robert Gault]

John, I'm not convinced your example is correct. With 252 and 255, you
are telling the GIME to use a screen that is 640x255 with 2 color
resolution (252) or undefined color resolution (255). The first screen
is quite normal and you can almost draw on it with the high res graphics 
commands.

The second should be very unpredictable as the GIME has not been given a
color resolution.

John Kowalski wrote:
><snip>
> There may actually be some evidence of what *might* have been the "256"
> color mode even in production CoCo 3s.  Here are two examples:
> 
> 10 POKE 59078,33:HSCREEN2
> 20 POKE 65433,252
> 30 GOTO 30
> 
> The first poke is just to stop the screen from clearing so you can see the
> random junk in memory display.  What you see is incomplete/unresolved
> graphics mode that appears to use 16 bits *PER* pixel - well, sort of..
> Only one out of 16 bits is actually active and the other 15 are ignored.
> 
> This shows that the pixel data bit shifter can be disabled.
> 
> Example two:
> 
> 10 POKE 59078,33:HSCREEN2
> 20 POKE 65433,255
> 30 GOTO 30
> 
> The one shows you a clean blank screen.  There is where a 256 color mode
> would have logically been mapped had it existed.  The GIME hardware is still
> addressing video RAM as expected - just not displaying any of it on the screen.
> 
><snip>