Sean Breheny wrote:

> Often CGA cards had both the 9-pin CGA connector AND a composite video
> RCA jack, which can be directly connected to the composite video in on
> an NTSC TV or VCR.

  Trick:  One chip IIRC, had a set of outputs which according to PCB
assembly, either went to the DE-9S directly (or via snubber resistors)
or to a resistor matrix to feed the RCA jack.  A link option apparently
determined whether the colour outputs were RGBI or R-Y,B-Y,I modulated
with the subcarrier.  I think another link option also selected
operation as either CGA or Hercules/MDA.

  Frequencies and standards?  The "Winn Rosch Hardware Bible" might be
in a library somewhere.  CGA was in fact NTSC scan frequencies.  They
*still* sell oodles of video games with TV output, for obvious reasons,
so it is little surprise the PC was so designed at the start.
--
  Cheers,
        Paul B.