[Coco] SVGA monitor
gene.heskett at verizon.net
Sat Oct 17 00:32:02 EDT 2009
On Saturday 17 October 2009, RJRTTY at aol.com wrote:
>In a message dated 10/16/2009 4:12:33 P.M. Eastern Daylight Time,
>msmcdoug at iinet.net.au writes:
>RJRTTY at aol.com wrote:
>>> It does but all that is internal in the AL250 scan
>>> doubler chip. It handles NTSC and PAL and my
>>> converter can use either mode....
>>Well I'm confused then. How do you get a 60Hz frame rate from a 50Hz
>>with only a line doubler???
>I have no idea. :) I just assemble the components and
>they do the work. I do know that the output for the
>PAL mode is cleaner than for NTSC. Don't know
>why that happens either. Perhaps it is because the
>PAL signal is generated outside the GIME chip.
Entirely possible Roy. The only 87 gime I have has extremely puny output
drivers in its RGB circuitry, with rise & fall times in the 350ns area. Not
to mention a visible noise level from the 14 mhz clocking on my 100mhz scope.
Short of jacking up the vcc, which may blow a chip made out of pure
unobtainium, I have NDI how to improve that situation. That puniness is I
expect, exactly why RS had to design in some external transistor buffering
stages for those 3 signals. They are in fact very good, 0 loss of rise &
fall times going through the buffers, its the puny signals from the gime that
are the problem.
Humm, that said, I also know at one time someone posted to this list several
years ago now that allowed as how they could spare about 50 of them, somebody
with Williams I believe, did anyone buy up a contingency supply, like Mark?
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