classic computer/game machine color video generation

Eric Smith eric at
Wed Jun 4 19:05:11 CDT 2008

Charles wrote:
> OK, so how close am I?

What you described is fairly close to how the IBM CGA adapter generated
composite video.

For the chroma signal, rather than a shift register, they used three
flip-flops clocked in such a manner as to produce six color phases
(three phases and their 180 degree opposites).  Three bits of the
pixel value drive an 8:1 multiplexer to select one of these colors,
or black or white (mux inputs tied to logic 0 or 1).


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