Re: SX clocks generation (was: 6569 luminances)

From: Segher Boessenkool <>
Date: Fri, 3 May 2013 02:01:38 +0200
Message-Id: <>
> Meaning the level of the luma varies from pixel to pixel (or more  
> than one pixel - haven't counted/measured so can't say now exactly  
> how wide the period of this wave is but looks close to two pixels)  
> creating various patterns in place where a solid colour would be  
> expected (at least horizontally). Various, because it seem to  
> depend on which colour is actually selected.

There are nine vertical stripes per sixteen pixels.

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.

> I am wondering if anyone knows (before I start disassembling the SX  
> in order to experiment) whether this effect can be caused by the  
> differences in the clocks generation methods between regular 64 and  
> the SX or something else (like the output amp).

It looks to me like the chroma signal is imprinting on the luma
signal; this happens somewhere at the output end, not at the
clock gen.  But you haven't described the clock gen construction,
so we cannot really tell :-)


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Received on 2013-05-03 01:00:03

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