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From: curtis@uwmacc.UUCP (Alan Curtis)
Newsgroups: net.micro.pc
Subject: Writing directly to screen memory
Message-ID: <442@uwmacc.UUCP>
Date: Thu, 30-Oct-86 18:17:34 EST
Article-I.D.: uwmacc.442
Posted: Thu Oct 30 18:17:34 1986
Date-Received: Fri, 31-Oct-86 02:44:11 EST
Distribution: net
Organization: UWisconsin-Madison Academic Comp Center
Lines: 21

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 have a few turbo programs that write directly to screen memory 
without doing any kind of checking for scan status, and I'm hoping
that this isn't doing any damage to the monitor.

Thanks,
-- 
Alan Curtis
Madison Academic Computing Center
ARPA: curtis@UNIX.MACC.WISC.EDU  
UUCP: {harvard,ucbvax,allegra,ihnp4,seismo}!uwvax!uwmacc!curtis