Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site ubc-cs.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!lll-crg!dual!qantel!ihnp4!alberta!ubc-vision!ubc-cs!ludemann From: ludemann@ubc-cs.UUCP (Peter Ludemann) Newsgroups: net.micro.pc Subject: Re: Addition help with Video Retrace Code Message-ID: <1208@ubc-cs.UUCP> Date: Fri, 9-Aug-85 01:17:04 EDT Article-I.D.: ubc-cs.1208 Posted: Fri Aug 9 01:17:04 1985 Date-Received: Tue, 13-Aug-85 01:46:16 EDT References: <1884@druxq.UUCP> Reply-To: ludemann@ubc-cs.UUCP (Peter Ludemann) Organization: UBC Department of Computer Science, Vancouver, B.C., Canada Lines: 24 Keywords: IBM-PC colour monitor snow Summary: An easier way to avoid snow. In article <1884@druxq.UUCP> bradley@druxq.UUCP (DavidsonBC) writes: >This is a different way to control the monitor to remove the fuzz or >snow. The snow is caused by the video chip and the CPU trying to >access the same section of memory at the same time ... > > The basic way to avoid the snow is to avoid contension for the > video buffer, the most reliable way to do this is to disable > the video while writting to the video buffer. There's a much easier way. One of the bits in a port for the video controller tells you whether or not the monitor is doing retrace. Just loop busily while the bit says retrace isn't happening and then write your bit of the screen. I managed to write about 100 characters without any snow but I suspect more are possible. I don't have the code handy, but if anyone's interested, I'll look it up and post it. But if you've got the IBM Tech Reference handy, it shouldn't be hard to figure out. One thing: my own IBM-"compatible" doens't have the snow problem and leaves the port looking as if retrace never happens. The scren writing program ran at least twice as fast as on the IBM-PC. And both were much faster than using BIOS. ubc-vision!ubc-cs!ludemann.UUCP