[Coco] Coco-3 to the GBS-8220 upscaler interfacing

[Steven Hirsch]

On Tue, 3 Jun 2014, Kandur wrote:

> Recently I got nostalgic and bought a Coco-3 on eBay, got it running and 
> trying to run NirtOS-9 on it. I really have to start from scratch, I 
> seem to have forgotten everything I knew about the Coco. At the moment 
> I'm trying to interface my Coco-3 with an LCD VGA monitor, using the 
> GBS-8220 upscaler board. I need to fix the sync somehow, to make the 
> output more stable. I read a post here from Gene, he used a 74LS04 to 
> combine the Coco's HSync and VSync outputs then connected them via 1n914 
> diodes to a 1800 ohm resistor, and to the S pin of the GBS-8220 board. 
> He wrote:  '(see the schematic)', but I can't see it. (: Any help 
> regarding the Coco-3 to the GBS-8220 board interfacing would be much 
> appreciated.

See: http://www.epanorama.net/circuits/vga2rgbs.html

The second diagram (VGA to RGB+CSYNC) will do the trick.  It's probably 
possible with fewer gates, but this circuit works very well.  Having said 
that, the GBS-8220 board does not yield a very clean display.  Definitely 
useable, but not pretty.



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