TTL RGB ==> PC

17 Nov 2007

...
   I don't
think I ever owned a CGA monitor that got
 brown correct.  
  I was going to say isn't that largely dependent on
 the monitor used? A non-issue w/a newer analogue
 monitor, that is if the voltage was correct. But you
 could always vary the resistance on that particular
 line, no? 
The point is (and we had a thread on this some time back), the colour 
mixing _seems_ obvious -- R,G,B turn on their respective electron guns 
and I turns on all guns a little bit. But if you have a real 5153 CGA 
monitor, or most EGA monitors in CGA mode (the 5154 is certainly like 
this), it gets a little more compiclated. Colour 6 (Brown), corresponding 
to R and G both asserted, is detected by circuitry in the monitor, and 
you get less green than you'd expect (the green gun is not driven so 
hard), giving brown rather than dark yellow. 

A simple resistor/diode circuit won't do this. You might not care (you 
will get viewable colours without it), but if you want to do things 
perfectly, you need to be aware of this.

-tony

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TTL RGB ==> PC