Newsgroups: comp.sys.atari.st.tech
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!ira.uka.de!fauern!faui43.informatik.uni-erlangen.de!csbrod
From: csbrod@immd4.informatik.uni-erlangen.de (Claus Brod)
Subject: Re: Overscan help needed
Message-ID: <1991Apr4.155259.15889@informatik.uni-erlangen.de>
Organization: CSD., University of Erlangen, Germany
References: <9546@star.cs.vu.nl>
Date: Thu, 4 Apr 1991 15:52:59 GMT
Lines: 25

rfschaa@cs.vu.nl (Schaaf R F ) writes:

>  I have a simple problem: I have a program that requires more than
>the standard 200 lines in color. I know it is possible to use the
>bottom border, but how?
>  If there is anybody out there that can explain me how to do it, please
>let me know.

You'll have to toggle from 50 Hz to 60 Hz or vice versa in the right
moment. This is done by writing to a shifter register. The switch
direction depends on the frequency that is currently selected for
displaying screens. The right moment is at some time in the last
scan line, so you'll have to install some timer B routine to get an
interrupt in the desired scan line.

This is from memory; I'm not really an expert in things like this.
I played with it once on my ST, and I did some similar hacks to
my ol' 64, but I never completed the work.

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Claus Brod, Am Felsenkeller 2,			Things. Take. Time.
D-8772 Marktheidenfeld, West Germany		(Piet Hein)
csbrod@medusa.informatik.uni-erlangen.de
Claus Brod@wue.maus.de
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