[Lancelot] VGA clk

H. Peter Anvin hpa at zytor.com
Tue Feb 22 18:00:58 PST 2005


Wei Mark Fang wrote:
> I tried using 25Mhz for the FSM that generates the
> timing signals, and set the clk of the DAC at 50Mhz
> (same as SDRAM). The result is not good. I programmed
> it to display 2 columns of different colors. However,
> it showed zig-zags of the 2 colors, all misaligned. 
> 
> I thought about the fact that the DAC is at twice the
> freq as the timing FSM. Doesn't each line appear
> stretched out? I mean the DAC is clocking each pixel
> twice, so the scanner will refresh 2 pixels with the
> same value. How must the timing FSM be adjusted to
> account for that? I am quite unsure, as I don't have a
> very good grasp of how VGA monitors work.
> 

It should shift the picture over by 4 pixels.

	-hpa



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