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

From: Mia Magnusson <>
Date: Sat, 2 Sep 2017 23:58:53 +0200
Message-ID: <>
Den Sat, 2 Sep 2017 10:00:21 +0100 skrev smf <>:
> On 02/09/2017 03:10, Mia Magnusson wrote:
> > Well, as long as you can store about one line you could tweak the
> > clock frequency of the computer so that it produces 624 lines every
> > 1/25 second, and then just insert one extra line on every other
> > field.
> Are you saying:
> You would have to change the clock speed so that two VIC frames
> equals one interlaced frame.


> But all the lines will be out of sync and so would need to be
> digitised and clocked out at the correct time & the proper syncs
> generated, to create the extra half line gap in the middle. Buffering
> data from vic and varying how much to delay it on each line to match
> legal hsync.

Yes, that's about the only way to get a correct signal from a C64.

> My thoughts:
> That should be in tolerance for tape loading, I'm not sure about disk 
> fast loaders.

Well, both tape speed and disk clock can be changed.

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...). It would be stupid if C= hadn't changed
the frequency in the direction that gives a more stable 50Hz v-synk.
(Stable V-synk means that the picture of a CRT screen will be steady
even if some mains powered transformer induces magnetic fields onto the

> It would cause real bad field seperation artifacts with horizontal 
> movement. You would be ok on a CRT because the phosphor would decay,
> but LCD TV's don't do this (some LCD TV's that display progressive
> analogue video also suffer from this problem).

I would had thougt that the reason for doing this would be to make it
possible to feed the C64 signal onto professional video equipmet for
some kind of broadcast stuff. Otherwise there is no real point in doing
it as far as I see it.

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Received on 2017-09-02 22:01:54

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