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The constants provided in the documentation for the subcarrier DDA values
assumed the clock was programmed to precisely 108MHz, but the PLL can't hit
that value exactly (or our PLL computation can't, in any case). The
result was an incorrect subcarrier frequency which resulted in synthetic
subcarrier phase shift and a lovely rainbow effect on the screen.
Unfortunately, the documentation didn't exactly describe the function
performed by the subcarrier clock hardware, so a bit of detective work was
needed. New constants were computed using the code in tv.5c and those, along
with lots of other values from the documentation were inserted into the
necessary tables.
The result appears to generate stable NTSC video on the svideo connector.
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