Apple II timing vs. NTSC (was Re: Good Composite->VGA converters for classic computers (& video games...)

[Jim Leonard]

Eric Smith wrote:
> Eric Smith wrote:
>> The Apple II horizontal rate is 228.0 times the color subcarrier
>> frequency, so that the color phase is the same on every line.
> 
> Jim wrote:
>> Was there a reason for this design decision?
> 
> It was done so that the same bit pattern that produces green on one scan
> line also produces green on the next scan line, rather than purple.  This
> is especially important for the low-res graphics mode, but not doing it
> would also have made the high-res mode harder to use.

Hm... I use the same bit-pattern in composite color on an IBM CGA, and I 
see that same behavior, so does that mean IBM CGA is doing the same 
thing, or is the card reversing the supplied bit pattern on every 
alternate scanline?
-- 
Jim Leonard (trixter at oldskool.org)            http://www.oldskool.org/
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