99% of VGA monitors cannot sync to a horizontal frequency lower than about
twice that of a television (i.e. most VGA's can't do less than about 30
kHz.) Some really old VGA monitors will, but I wouldn't expect that people
are going to own these monitors.
A workable solution would be to store the data from each scanline in a
buffer. Once full, output the buffer at twice the speed, and do it twice.
In fact this is exactly what many simple TV to VGA converters do.
>From: Adam Wozniak <adam@xxxxxxxxxxxxxxxx>
>Reply-To: stella@xxxxxxxxxxxxxxxxxx
>To: stella@xxxxxxxxxxxxxxxxxx, <fpga2600@xxxxxxxxxxxxxxxx>
>Subject: [stella] problems with monitor syncing
>Date: Mon, 2 May 2005 17:38:21 -0400
>
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>http://cuddlepuddle.org/~adam/help/
>
>These are images of my FPGA TIA driving my VGA monitor. (Space Invaders,
>if you can't tell.)
>
>It looks as though the monitor cannot sync to the horizontal frequency
>I'm giving it. The image is totally stable vertically (i.e. no rolling
>or anything), but it looks as though each line is wrapped around the
>screen twice (one and a half times?). Look closely at the score; note
>the large gaps between pixels, both horizontally and vertically.
>
>Unfortunately I don't have a scope handy to measure frequencies.
>
>Is it possible my hsync is correct, but that my monitor sucks? Or have
>I done something else wrong?
>
>- --
>adam@xxxxxxxxxxxxxxxx http://cuddlepuddle.org/~adam
>KG6GZR http://cuddlepuddle.org/~adam/resume.html
>
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