[Coco] RGB --> VGA for CoCo: A success story

[RJRTTY at aol.com]

In a message dated 1/31/2009 2:12:56 P.M. Eastern Standard Time,  
gene.heskett at verizon.net writes:



>Blue text on a black background never reaches more than 5% of white,  and 
the 
>reversed situation of blue text coming down from white is also  only about 
5% 
>amplitude due to very very slow rise and fall times  compared to the 'dot 
>clock' itself, with the overall amplitude being  nstc gain trimmed by the 
time 
>the gime outputs it.  That alone  restricts the voltage swing of the blue 
>signal to under 100 millivolts  right there.  Roy's converter doesn't throw 
a 
>thing away that the  gime doesn't do to a far worse degree.  If it were 
>possible to  bypass the gime's 2 bit output d/a's easily, I'd do it in a 
heart  
>beat.  But I'm not sure how one would go about capturing the memory  read 
>intended to feed the d/a's and do that.  All in the latch  decoding and 
timing 
>I expect, and an 8 bit data latch with 4, 2 resistor  groups of 2+2r could 
>handle the rest, at a far more usable bandwidth  delivered to the monitor.

>Roy, might that be the next project?   2, maybe 3 all cmos chips I'd think.  
>Cutting it into the coco3's  circuitry, once the thing is ready as a kit, 
>would be a bit scary for  the soldering iron challenged, but again, not 
>impossible.  I'll be  a guinea pig any day as I have a spare cc3 and I know 
>which end of the  soldering iron gets hot. Hint, hint.


The blue channel has always been a problem with my converter.
The red  channel has the same problem but to a much lesser extent
for some  reason.   All I can think of is that these signals are out of
sink  with the dot clock and the old monitors covered it up very well.

I have  NDI how to bypass the gime.   Like you say Gene it would be  a
"scary" soldering job on the motherboard.   I might do it someday  on
one of my spare coco3's just to see what a perfect output would  look
like......stray tuned.

Roy
 
**************From Wall Street to Main Street and everywhere in between, stay 
up-to-date with the latest news. (http://aol.com?ncid=emlcntaolcom00000023)