[Coco] 65k colours serial VGA module

[John Kent]

On 21/05/2012 10:20 PM, jdaggett at gate.net wrote:
> John I do remember investigating the original release of that module 
> back about three years or more ago. Then I thought it was to expensive 
> for what it did. Furthermore it did little to improve what was already 
> apart of the COCO or any 6809 based system. back then the serial speed 
> was to slow and the onboard memory was to limited to do more than 8 
> bit color and at 640x480 resolution. The newer module thought may have 
> been greatly improved to finally do some of the promise the original 
> Picaso Module had hope to do. james

Hi James,

For some reason when I trim emails from some people, the text gets 
compressed.

What I was thinking with an FPGA solution was that it might be possible 
to lock the FPGA clock to the CoCo video pixel clock so that the bus 
snooping was synchronous with the CPU. There is probably not enough pins 
on the XuLA board to do bus snooping, VGA drive and have some way to 
send commands to it, but perhaps the bus snooping and programming can be 
done using the same data bus pins.

I bought a number of 74LVC245 (?) data bus transceivers that are 
supposed operate at 3.3V and are 5V tolerant. I bought a bunch of SSOP20 
pin breakout boards off eBay that I thought I could solder the chips to 
and mount as DIP packages on a prototype board. If you can snoop the 
video as Mark suggests then you can overlay it on the video output of 
the FPGA graphics generator.

If you can double the pixel clock and line rate you may be able to drive 
a VGA display with the CoCo output. i.e. the FPGA graphics controller 
would double as a scan rate converter.

John.

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