[Coco] CC-Five (was Re: Pseudo CoCo4???) (LONG)

[jdaggett at gate.net]

On 24 Jan 2007 at 16:33, Mark McDougall wrote:

> Dan Olson wrote:
> 
> > The only thing you can do in this case is to make the hardware run
> > the old software well enough to be useful without the use of new MMU
> > or expanded modes.  This is exactly the same as the CoCo3, really. 
> > I own a CoCo2 and of course can't use any CoCo3 software, get enough
> > new hardware out there and the new software will follow.  If you
> > don't want to have hardware with no software support, then the new
> > system would have to be basically the same as current CoCo hardware,
> > just faster clock speeds, VGA or DVI output with the current video
> > modes, etc.
> 
> Agreed. IHMO the *only* way a 'Coco4/5' is going to get any "market
> acceptance" is if there is a legacy mode which runs all coco1/2/3
> software unaltered. This is another reason why attempting to implement
> a stock Coco1/2/3 is a good first step in the whole process.
> 
************

This is not so much a problem.  Just may require more real estate in an FPGA.

> Of course there's no reason why it can't have "transparent"
> enhancements such as VGA/DVI output, or user-selectable clock speed
> for example.
> 
> Once we get that in place, we can add features like enhanced graphics
> mode support. I suspect the early adopters will be people like James
> McKay who are actively developing Coco software (16-colour "Glove"
> James?). Next will be people who patch existing coco games to, for
> example, change the ghastly 4-colour palettes! From there it'd be nice
> to see Nitros-9 drivers being updated as well - 80x25 *text* mode
> screens would be nice...
> 
> Regards,
> Mark

Actually  to improve color resolution would be to have an extra bit set in say the INIT1 
register that would be say for COCO 4. This would then allow bit 6 and bit 7 of the color 
pallette to be written. Therefore you now have a pallette of 16 colors of 256. There could be 
another trick to swap the pallette register bank  with writes to a register to map in banks of 
16  colors. This would keep some backward compatibility. As for increase resolution there is 
an unused bit in video resolution register at $FF99 Bit 7 in combination with bits 6 and 5 to 
double the lines per frame. 

There are also unused adresses in the $FFC0 to $FFDF range that is used by the Coco1 
and 2 but not the COco3. Subsequently the CCOC4/5 could use. 

james