[Coco] SVGA monitor

jdaggett at gate.net jdaggett at gate.net
Sat Oct 17 09:11:52 EDT 2009

On 17 Oct 2009 at 0:13, 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 
> source 
> >with only a  line doubler???
> >Regards,  
> 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.
> Roy


Does you scan doubler use the PAL composite output or the PAL RGB outputs 
from the PAL Coco3? If the composite output from the PAL Coco3s were used 
then that would explain why there is a difference. For one, better filtering in the 
output. The RGB output buffers are same for PAL and NTSC versions. 


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