Path: utzoo!attcan!uunet!fernwood!decwrl!elroy.jpl.nasa.gov!hacgate!tcville!sed170!lee
From: lee@sed170.HAC.COM (John Lee)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Am I even or odd?
Summary: Look in the hardware manual
Message-ID: <342@sed170.HAC.COM>
Date: 10 Mar 90 00:27:15 GMT
References: <1958@ursa-major.SPDCC.COM>
Reply-To: lee@sed170.UUCP (John Lee)
Organization: Hughes Aircraft Co., El Segundo, CA
Lines: 22

In article <1958@ursa-major.SPDCC.COM> denbeste@ursa-major.spdcc.COM (Steven Den Beste) writes:
[...]
>	2. A way to find out during the vertical retrace which field will be
>	   the next to be shown.
[...]

I developed a driver for a pair of 3-D glasses using the vertical-blank
interrupt exactly as you described.  A bit in one of the video register
identifies the current frame (long or short), and is documented in the Hardware
manual.  I don't have it with me here at work, but I think it's the high bit
of the beam vertical position register.  Since you're using an assembly
routine to access the register, be sure to use the custom register base
passed to you and the symbolic reference provided by Commodore.

--John Lee
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The above opinions are those of the user and not of those of this machine.