[Coco] RGB2VGA on DE0-Nano (improvements)

[Retro Canada]

it doesnt need to replace the gime/6847 inside the coco. since the bus is available at cartridge port we could do a passive 6847/gime that duplicate the ram externally (grabing all writes) and all registers to generate a video from the fpga external ram. 

that would be fairly simple to start with the 6847 which is simpler. a good idea for a project :)

On Aug 30, 2014, at 10:20 AM, Gene Heskett <gheskett at wdtv.com> wrote:

On Saturday 30 August 2014 08:07:57 Mark McDougall did opine
And Gene did reply:
>> On 30/08/2014 8:33 PM, Gene Heskett wrote:
>> any sampling is likely something that would need
>> addressed not by grabbing the RGB output of a software GIME chip or a
>> 6847, but by grabbing the data straight from memory as it is
>> delivered to those chips and generating the VGA completely external
>> to any emulation of the coco's color generating chips.
> 
> Which is exactly how the Carte Blanche (Apple II) and MISE (TRS-80
> Model I) do the job. Much easier, much cleaner, and more flexible.
> 
> Then you have the F18A for the TI99/4A, an FPGA-based drop-in solution
> that is commercially available for the TI99/4A, which is what Gene
> goes on to dream about! ;)
> 
> <http://codehackcreate.com/archives/30>

Interesting. He did that in a 250k gate device, so the rest of the gime 
might need a 500k gate device.  But it would need the 84 pin square 
footprint of the existing gime if it is to be just plugged in.  In my 
machine, with a 2 meg dram kit in it, expansion real estate for the level 
translators needed would be hard to find as nearly all of it would have to 
be obtained in a direction toward the keyboard.

But since my next birthday will be the 80th, I don't think I will embark 
to duplicate his work and a memory manager too.

> So... not outside the realm of possibility for the Coco!

No its not, but it will take someone with confidence that they have enough 
time to complete the project.  My recent episode with a pulmonary embolism 
has reminded me that none of us have a tomorrow guarantee.  Other than my 
arthritis/scoliosis pain, I feel better than I have in 10 years.  But that 
doesn't extend my warranty.

> Regards,


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
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-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS

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