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From: thomas%spline.utah.edu.uucp@utah-gr.UUCP (Spencer W. Thomas)
Newsgroups: comp.sys.mac
Subject: Re: Spectrum card from SuperMac
Message-ID: <2261@utah-gr.UUCP>
Date: Tue, 1-Dec-87 18:42:57 EST
Article-I.D.: utah-gr.2261
Posted: Tue Dec  1 18:42:57 1987
Date-Received: Sat, 5-Dec-87 06:08:19 EST
References: <2289@Shasta.STANFORD.EDU>
Sender: news@utah-gr.UUCP
Reply-To: thomas%spline.utah.edu.UUCP@utah-gr.UUCP (Spencer W. Thomas)
Organization: University of Utah CS Dept
Lines: 31

In article <2289@Shasta.STANFORD.EDU> kaufman@Shasta.stanford.edu (Marc Kaufman) writes:
>I am looking for some information about the Spectrum video card  ...
>1. The box says that the board operates at 640x480 and 1024x768
I haven't figured out how to do this.  The "manual" that comes with it
has lots of pictures of video cables, but no indication of how to get
a different resolution.  (In fact, no programming info at all.)

>2. What is the Horizontal Scan rate?  I may want to use my own monitor.
About 48 KHz.  I haven't figured out how to change this, either (the
manual is just as silent).  Any 19" (1K resolution) monitor based on
the Trinitron tube should work (we are using one from an HP "Bobcat").

>3. Every demo unit I have seen, using the SuperMac monitor, has an annoying
>   vertical artifact, consisting of purple lines, when a uniform gray
>   background is selected.

This is a moire pattern that results because the pixel size is
slightly different than the phosphor line spacing on the Trinitron
tube.  If you select a different background pattern, it changes (or
goes away).  The background is not "a uniform gray", it has every
other pixel on.  This is about the worst background you can choose for
showing up moire patterns.  If you don't care about making the pixels
on the Supermac screen spaced 72/inch, you can probably tweak the size
controls on (inside) the monitor and make it either better or worse.

Or you could really use a solid gray background pixmap...




=Spencer   ({ihnp4,decvax}!utah-cs!thomas, thomas@cs.utah.edu)