[Coco] Kicking the Z-80 butts...

[Hugo Dufort]

As I have mentioned in another discussion recently, had Tandy moved away 
from the VDG & designed their own "slightly improved VDG" at the time of 
the Coco2, they could have supported some additional low-res video modes 
with some very interesting features. All within the 64k limit, and 
aligned to the 1.5k video pages (PMODE/CPLEAR), respecting the existing 
limits, e.g. PCLEAR8.

For example:
64x96 x256colors (6k/screen)
128x96 x16colors (6k/screen)
128x96 x256colors (12k/screen)
128x192 x16colors (12k/screen)
256x192 x4colors (12k/screen)

+RGBI palette support for all these modes (available: the 64 EGA colors 
x4 shades)

This would have paved the way to higher resolution 16-color and 
256-color modes in the Coco3. But at this point, we wouldn't have been 
able to map 256x192x256colors high-memory pages to low-memory pages in 
an efficient way. Addressing this mode would have been complex, 
especially for full-screen game development. I really think the maximum 
workable resolutions for the Coco3 (limited to 64k low memory, whatever 
the addition memory is) would have been:
160x200 x256colors
320x200 x16colors

But it's all speculation and "in hindsight", of course! ;)

Hugo

Le 2015-04-28 15:20, Zippster a écrit :
> Well, it is late ‘70s technology.  Earlier that decade the first microprocessors were introduced.
> I guess the 6847’s major weak point is probably the terribly limited 32 column text display.
> Other VDGs of the time were pretty low-resolution as well.  But you have to remember there
> wasn’t much resolution available on the display devices either, even if you would have had the silicon for it.
>
> Video is just a massive amount of data once you start to move past 300x200 or so and just a few colors.
> Even the 6809 will start to choke pretty quickly heading in that direction.
>
> Although it is a pretty incredible 8-bit CPU with an interesting story behind it.
> It should have been more popular.
>
> - Ed
>
>
>> On Apr 28, 2015, at 1:28 PM, Gustavo Ranaur Schoenaker <ranaur at ranaur.net> wrote:
>>
>> Really amazing.
>>
>> The more I know the 6809 the more I think the problem with the chip was no
>> t the processos, but the 6847. Maybe it was the reason Tandy made the GIME
>> chip on CoCo 3. Video is really the upper limit of the plataform. At those
>> times the video chip make a huge difference.
>>
>> Nice job Luis!
>>
>


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