[Coco] RGB video on CoCo3

[Robert Gault]

Phill Harvey-Smith wrote:
> Success !
> 
> I have now got RGB working, and it provides a much better picture, for 
> the first time I can actually use NitroOS9 in 80 column mode and read 
> the text !
> 
> My problem was that I was not feeding +5V to Pin 16 on the SCART 
> connector, so the TV was interpreting my signals as Composite video, 
> which is why it was way to bright. Ended up examining my BBC micro scart 
> cable which I knew worked, and was a machine of a similar age.
> 
> Once I did this I could feed the signals direct from the CoCo to the TV 
> and it produced a picture without problems, though a little bright, 
> placing a set of 120R resistors inline with theRGB signals seems to have 
> brought the brightness down, though it does seem a little more noisy, 
> maybe due to impedence mis-match....analog electronics was never my 
> strong point.
> 
> 
> One thing I did notice in ECB was that the CLS colours are slightly 
> different :-
> 
> CLS    Composite/TV    RGB
> 0    Black        Black
> 1    Green        Green
> 2    Yellow        Blue
> 3    Blue        Orange
> 4    Red        Grey
> 5    White        White
> 6    Greenish    Yellow
> 7    Purple        Red
> 8    Pink        Light blue
> 9    Green/MS    Green/MS
> 
> Allowing for the fact that this is an NTSC CoCo3 on a PAL TV, though it 
> is NTSC capable, and the fact that I'm slightly Red-Green colourblind, 
> is this normal ?
> 
> Cheers,
> 
> Phill.
> 
> 

I don't know whether you did this, but both Basic and OS-9 require you 
to tell the system whether a CMP or RGB monitor is in use. There are two 
sets of default palette colors, one for CMP and one for RGB. Basic 
defaults to CMP as does OS-9, and NitrOS-9 now has the default monitor 
selection in Init.
If all you do is change to an RGB monitor instead of a composite, the 
default colors will indeed be wrong.

For Basic enter RGB to get those colors. For OS-9 (without making any 
changes to the system) enter montype -r. If you want permanently to 
select an RGB monitor for NitrOS-9, change Init byte $25 from 0 to 1.