Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!lll-crg!nike!ucbcad!ucbvax!cartan!brahms!ballou
From: ballou@brahms (Kenneth R. Ballou)
Newsgroups: net.micro.pc
Subject: Re: Writing directly to screen memory
Message-ID: <155@cartanBerkeley.EDU>
Date: Thu, 30-Oct-86 22:52:05 EST
Article-I.D.: cartanBe.155
Posted: Thu Oct 30 22:52:05 1986
Date-Received: Fri, 31-Oct-86 14:13:43 EST
References: <442@uwmacc.UUCP>
Sender: daemon@cartanBerkeley.EDU
Reply-To: ballou@brahms (Kenneth R. Ballou)
Distribution: net
Organization: Math Dept. UC Berkeley
Lines: 22

In article <442@uwmacc.UUCP> curtis@uwmacc.UUCP (Alan Curtis) writes:
>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.  

	The word "safe" here refers to avoiding "snow" on the screen.
This is the procedure to avoid creating snow when updating the screen
on older video cards.  Newer cards have no problem with direct screen
writes.

---
Kenneth R. Ballou		...!ucbvax!cartan!brahms!ballou
Dept. of Mathematics
University of California
Berkeley, California  94720