[Coco] Coco 3 pixel clock
lamune at doki-doki.net
Tue Oct 9 18:44:26 EDT 2007
Mark McDougall wrote:
> Christopher Hawks wrote:
>> It looks great (with my Hsync delay circuit to center it), but appears
>> to be missing about every eighth dot on the screen. If I move the
>> display horizontally, the missing dots change so I suspected it is a
>> difference in pixel clock rates. This occurs in all resolutions (640,
>> 320, and 256).
> If you _really_ wanted to, you could probably implement a pixel-clock
> converter with a CPLD and some video RAM as a line buffer... there might
> be a simpler way (I'm no video guru) but that's how you'd do it inside
> an FPGA...
I sorta did something like that- I ran a 512x200 plasma display with a
CoCo 3 (probably about 15 years ago at this point)
The pixel clock in the CoCo is of course derived from the 28.63636
crystal. I simply "h4x0r3d" out the crystal and replaced it with a TTL
can oscillator. I then tapped the output to divide down to something the
plasma display could accept.
Something similar might work today. It was relatively minor surgery.
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