Constant, Oops. This part is inaccurate:
"[ ... ] The bits needed to draw the screen image are only accessed on the "forward" sweep, while the gun is "off" during the retrace." The screen memory is being accessed during the whole process, but the gun is "off" during the retrace, making it possible to hit the video RAM during that part of the cycle without snow. The trick is to do your splashing around in the video RAM during either the horizontal retrace or vertical retrace. The vertical takes more time, but there's only one of those per refresh, while the horizontal is quicker, but there are, what, 200 or more in a refresh. ~~Garry [EMAIL PROTECTED] Original Message: ----------------- From: [EMAIL PROTECTED] [EMAIL PROTECTED] Date: Mon, 1 Oct 2001 13:19:12 -0400 To: [EMAIL PROTECTED] Subject: Re: [SURVPC] snow on a CGA monitor Constant, The "snow" on a CGA monitor is caused by two devices accessing the video memory at the same time (the CPU and the video processing chip (I used to know the part number). There is a register on the card which can be read by a program and which indicates the state of the video processor at any given moment. Among other things it indicates when the electron gun in the monitor is in one of its retrace cycles. The bits needed to draw the screen image are only accessed on the "forward" sweep, while the gun is "off" during the retrace. -------------------------------------------------------------------- mail2web - Check your email from the web at http://mail2web.com/ . To unsubscribe from SURVPC send a message to [EMAIL PROTECTED] with unsubscribe SURVPC in the body of the message. Also, trim this footer from any quoted replies. More info can be found at; http://www.softcon.com/archives/SURVPC.html
