[Coco] COCO Video

[john dumas]

On 6/19/2013 2:39 AM, T. Franklin wrote:
> I think you're confusing the 6847 with the GIMI. The 6847 was a chip Developed by Motorola for a dumb terminal called TRS-80 VideoTex Terminal, for the farm industry (precursor to the CoCo). The GIMI was breadboarded with discrete components when developing the CoCo3.
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> https://en.wikipedia.org/wiki/TRS-80_Color_Computer
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> The logic of the 6847 is relatively simple and constructing a replacementfor it isn't outside of the realm of possibility. The thing was breadboardedwith discrete logic while being designed, after all.
If there was a breadboard of the VDG, it was well hidden from the folks 
at the Austin
Design Center! While doing the Time Domain Analysis of the VDG, I would 
have LOVED
to have a breadboard to compare with some of the race conditions and the 
one logic
error, I found....and had to correct.

A breadboard would also have very useful while testing the first 
silicon. If such a BB existed,
I wonder WHERE it lived? Has anyone actually seen it with their own Mark 
One eyeballs?

Oh and BTW, a BB would have prevented the surprise we got when the first 
silicon powered
up in one of the two "modes" - green or orange background......I 
remember the "What the...!"
expressions. Seems that all of us designers involved with the chip 
missed that "feature"
before finalizing the design.
My bad!


cheers,
johnd

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