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From: root@dialog.stgt.sub.org (Christian Motz)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech,comp.sys.amiga.hardware
Subject: Re: A3000 Video Chips
Message-ID: <2260@dialog.stgt.sub.org>
Date: 24 Jul 90 17:49:36 GMT
References: <4741@munnari.oz.au> <13060@cbmvax.commodore.com> <16713@windy.dsir.govt.nz> <1091@mpirbn.mpifr-bonn.mpg.de> <13110@cbmvax.commodore.com> <3003@medusa.informatik.uni-erlangen.de>
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Reply-To: root@dialog.stgt.sub.org (Christian Motz)
Organization: Dialog Software Development
Lines: 31

In article <3003@medusa.informatik.uni-erlangen.de> mlelstv@medusa.informatik.uni-erlangen.de (Michael van Elst ) writes:
>
>PAL specs don't say anything about phase relationship between sync signals
>and color burst. And the color is the phase shift between color sub carrier
>modulated onto the video signal and the color burst signal. I believe it's
>the same in NTSC.

I don't think this is quite accurate. As far  as  I  know,  the  color
subcarrier and the horizontal sync signal are coupled with  regard  to
phase. Since the color burst is  nothing  else  but  that  very  color
subcarrier keyed in during horizontal blanking, you actually do have a
relationship between the two.
   A note on the side: The differences between PAL and NTSC do not lie
within the basic principles, but the implementation. PAL uses  a  nice
scheme to get rid of phase shifts that occur between  the  camera  and
the TV set. For this, it trades some of the accuracy and brilliance of
the colors. But the basic concept of how to get  the  color  into  the
picture is exactly the same.


>Of course, the video clock (~3.58MHz) can be used to generate a color
>sub carrier. The C= RGB/PAL converter does this (I tried to use it with
>another computer but had to add a crystal to get it to work).

Yes, but it cannot be used directly to  generate  one.  The  principle
here is that you use it with a PLL to lock the  4. 43  MHz  PAL  color
oscillator in phase with all the rest of the circuitry. As a matter of
fact, this should be the exact way how the A520 does it.

--
Christian Motz                                root@dialog.stgt.sub.org