Re: Apple RGB monitor- VGA interface

[Rubywand <rubywand@swbell.net>]

James Poore writes ...
>
> ....
> Nothing will be gained by just doubling the scan rate to 30Khz.  You will
> still have 320 or 640 horiz pixels on the screen just doing it faster.
> ....
>

     True; that's why the design idea specifies doubling the dot rate
and displaying each line twice.

     Look at it this way: If the original Horizontal scan frequency is
15kHz (roughly 66 uSec/line for 320/640 dots plus H-blanking dots and
H-Sync/retrace), then, doubling the dot rate yields about 33uSec/line
for an H-scan frequency of 30kHz. 400 lines takes about .0132 Seconds.
Once we add the usual extra lines during Vertical blanking, we get a
frame rate which will fall within 60Hz-70Hz.

     Unless I've messed up somewhere in the above, it looks like
capturing lines and resending at twice the dot rate should work.


Rubywand