Re: SX clocks generation (was: 6569 luminances)

From: Segher Boessenkool <>
Date: Fri, 3 May 2013 17:51:39 +0200
Message-Id: <>
>> Internally on the VIC-II, there are two colour clocks, 90 deg out
>> of phase; one of-em is flipped polarity every other scan line.
>> So you see the "stripes" when the non-flipped component is dominant
>> for your colour, and the "checkerboard" when the flipped one is.
> That would explain. So in some colours one of the clocks is  
> "dominant" and with other colours the other, it seems. But what  
> means "dominant" here? That both are used with different level?  
> Those are clocks (as you wrote), not analogue signals, right? So  
> how can they be "dominant"?

I left out quite a bit, whoops :-)

So you have these two clocks, 90 deg out of phase.  Those two are
"digital" so far.  Then both of these signals and their complement
are driven to four identical circuits.  Those circuits are first
two low-pass filters (an opamp (well actually just two fets, i.e.
an inverter) wired as integrator) and then capacitively coupled to
another opamp (more interesting, four fets).  As end result you
get four sine-like waves out, each 90 deg shifted to each other.
These sines are combined in various ways to form the eight different
chroma signals; the colour per pixel decides which to use (if any).
Some colours have more of the phase that isn't flipped every line,
and some have more of the phase that _is_ flipped.


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Received on 2013-05-03 16:00:49

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