On average, we need a refresh about every 7.8 microseconds.  (This
refreshes one row.)  A 60Hz screen refresh is every 16.7 milliseconds.
Not fast enough, and you can't do more than 8 in a row.  At
[EMAIL PROTECTED], you get a scanline every 31.7 microseconds (not all of
which are active video).  (Of course, at that resolution, we take a
small fraction of that time to actually read the scanline from
memory.)

On 8/17/06, Koen De Vleeschauwer <[EMAIL PROTECTED]> wrote:
> With this design, memory refreshes can be
> postponed in favor of video reads.  As long as the average
> refresh rate remains constant, there won't be any problems.

Maybe I'm missing something, but why not issue a memory refresh during vertical 
sync?
Is there any advantage in postponing a refresh to a moment when pixels are 
being output?

regards,

koen

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