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  Article 4 of 58
  
Subject:      Re: question about horizontal retrace on pc.
From:         human@inf.utfsm.cl (Franco Catrin)
Date:         1995/07/26
Message-Id:   <3v5pni$g6@manutara.inf.utfsm.cl>
References:   <3v39e3$gdo@mn5.swip.net>
Organization: Universidad Tecnica Federico Santa Maria
Newsgroups:   comp.lang.asm.x86


Chris Rossall (chris.rossall@mailbox.swipnet.se) wrote:

: I wonder if anyone could tell me if there is a bit in the vga that
: signals a horizontal retrace.I know that there was one on the cga and
: a lot of programs checked this before writing to screen mem to avoid
: 'snow' on old cga cards.

: Thanks..

: -Chris

Read port 03dah bit 0 and bit 3 for vertical retrace.  I think it's the
same on CGA.  Anyway you haven't to check it to avoid 'snow' on a VGA
card.

                                                  Human

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