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From: darrylo@hpsrlc.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: terminal programs with zoom/pan
Message-ID: <3320066@hpsrlc.HP.COM>
Date: Wed, 11-Nov-87 19:23:11 EST
Article-I.D.: hpsrlc.3320066
Posted: Wed Nov 11 19:23:11 1987
Date-Received: Sun, 15-Nov-87 04:59:43 EST
References: <3449@uwmcsd1.UUCP>
Organization: HP Network Measurements Div - Santa Rosa, CA
Lines: 45

In comp.sys.ibm.pc, john1233@csd4.milw.wisc.edu (Thomas M Johnson) writes:

> Well, I am about to purchase a PC clone. (to be exact a American
> Research) and went to a friend's house to see it. (I'm buying it
> from him used but still under warrenty). Well, we called this system
> I'm on with his Avatex modem.
> 
> Everytime a CR was encountered, the screen would flash. He says that
> even happens where he works and it is the terminal program.
> I think it was PC-Talk.
> 
> Is this true? Is it the computer? Is it the modem?
> Are there any terminal programs that don't flicker?
> 
> 			      Tom
>                      john1233@csd4.milw.wisc.edu
> 			       or
>                          tommyj@lakesys
> ----------

     Let me guess -- he has a color graphics card, right?  I'm going to
assume that he does.  The "engineer" who designed the color graphics card
did not design it such that both the video section and the CPU could access
the video memory at the same time.  As a result, a small amount of garbage
can appear on the screen when the CPU accesses the video memory.  To make
things worse, the video circuitry outputs "white" (as opposed to "black",
which would have made the problem slightly less obnoxious) when the CPU does
so.

     To prevent lots of garbage from appearing on the screen when the CPU
accesses the video memory to do things like scrolling, there is code in the
BIOS to TURN OFF THE VIDEO while the accesses are being done, which causes
the screen to flash.  Yuk.

     With a 100% compatible color graphics card (there are some slightly
non-standard cards which fix this problem), the screen will ALWAYS flash
when scrolling.  Double Yuk.

     -- Darryl Okahata
	{hplabs!hpccc!, hpfcla!} hpsrla!darrylo
	CompuServe: 75206,3074

Disclaimer: the above is the author's personal opinion and is not the
opinion or policy of his employer or of the little green men that
have been following him all day.