Re: Difference in luma-chroma delay of C64/C128 compared to standard S-video

From: Mia Magnusson <mia_at_plea.se>
Date: Sun, 3 Sep 2017 00:18:38 +0200
Message-ID: <20170903001838.00006c3d@plea.se>
Den Sun, 3 Sep 2017 00:10:38 +0200 skrev Gerrit Heitsch
<gerrit@laosinh.s.bawue.de>:
> On 09/02/2017 11:58 PM, Mia Magnusson wrote:
> > 
> > But isn't this even how the clock in a C64 is already? We know that
> > the h-sync frequency is wrong to avoid some PAL dot crawl. (Dot
> > crawl is kind of a feature of PAL...).
> 
> I thought dot crawl happens if pixel clock and color clock are not in 
> sync? Like on a ZX Spectrum. With the discrete PLL in the C64 (and
> later the 8701), dot clock and color clock are in sync and that
> prevents dot crawl.

Yes, but AFAIK a correct PAL clock cannot be evenly divided to get a
correct PAL h-sync. (you need fractions in the divisor). Thus dot crawl
in a correct PAL signal.

15625 * 284 = 4437500 = too high
15625 * 284 = 4421875 = too low

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Received on 2017-09-02 23:00:41

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