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From: vg55611@ihuxk.UUCP (gopal)
Newsgroups: net.micro.pc
Subject: Re: Writing directly to screen memory
Message-ID: <1225@ihuxk.UUCP>
Date: Fri, 31-Oct-86 20:17:15 EST
Article-I.D.: ihuxk.1225
Posted: Fri Oct 31 20:17:15 1986
Date-Received: Mon, 3-Nov-86 20:15:41 EST
References: <442@uwmacc.UUCP>
Distribution: net
Organization: AT&T Bell Labs, Naperville, IL
Lines: 20

> I have been perusing through some assembler code written who knows where,
> and I noticed that when a particular routine writes to screen memory,
> it first reads the video controller scan status and makes sure it is 
> low, then after it goes low it waits until it goes high before writing
> to the screen buffer in memory.  The associated comment remarks that
> it must go high before it is safe to write directly to screen buffer
> memory.
> Is it possible to damage the monitor if the screen writes are not 
> synchronized with the scans, or is there some other explanation.  

I wrote a program sometime ago that writes to and reads from the screen
memory extensively and did not check the video controller scan status.
Never had any problems of any kind (the program has been in use for a
couple of years).

I have never seen any warning about doing this anywhere either. The
only thing I can guess is that this may prevent "snow". Some other
netlander may have a better guess.

Venu P. Gopal, ihnp4!ihuxk!vg55611