Path: utzoo!attcan!uunet!van-bc!root
From: lphillips@lpami.van-bc.UUCP (Larry Phillips)
Newsgroups: comp.sys.amiga
Subject: Re: Bug in decision for PAL or NTSC
Message-ID: <2016@van-bc.UUCP>
Date: 10 Dec 88 17:13:35 GMT
Sender: root@van-bc.UUCP
Lines: 50

> To clarify: PAL == 256 lines/frame, NTSC == 200 lines/frame.

> 
> PAL -> 50 Hz -> 25 frames/sec -> 6400 lines/sec
> NTSC -> 60 Hz -> 30 frames/sec -> 6000 lines/sec
> 
> So both need about the same dma bandwith to display a standard picture. You
> can't display 256 lines with NTSC, can you ??

NTSC is 262.5 lines per frame, 525 lines per field, ( I may have 'frame'
and 'field' mixed up here, never could remember which was which). Anyway,
you cannot use the entire frame, because some of the lines are eaten by
the retrace. Yes, you can display more lines on a PAL monitor than you can
on an NTSC monitor, but it doesn't matter, because..
 
> By looking at the line frequency at boot-time, the amiga should decide
> whether to display 200 lines (60 Hz, no dma-time for 256 lines) or
> 256 lines (50 Hz, no 200 lines please !).

..  the line frequency and the vertical frequency of the monitor are
completely separate things.  The only reason you can't get much use out of
a PAL television set in North America is because there are no TV stations
broadcasting in that standard. You can, however use a PAL VCR here,
feeding a PAL TV, and similarly, you can use a PAL Amiga with a PAL
monitor here, where the line frequency is 60 Hz (and it's a bitch to
get the power company to change it for you :-) )

  There are two things to look at, therefore, the line frequency, which
will determine the clock updates, and the vertical frequency, which will
determine the number of lines you can show on screen.  There are a couple
of entries in the ExecBase struct that tell you what both of these are on
the machine you are running, but I hesitate to point them out, for fear
that Leo will tell me I'm wrong again, without saying why.

> Still puzzled,

Hope this clears it up for you.
 
> Klaus

-larry

--
"Intelligent CPU?  I thought you said Intel CPU!" 
        -Anonymous IBM designer-
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|   //   Larry Phillips                                          |
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