[Coco] SVGA monitor

Gene Heskett 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? 

Cheers, Gene
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