Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 alpha 4/15/85; site amd.UUCP
Path: utzoo!watmath!clyde!amd!ching
From: ching@amd.UUCP (Mike Ching)
Newsgroups: net.micro.pc
Subject: Re: Trying to access vertical retrace.
Message-ID: <1951@amd.UUCP>
Date: Thu, 21-Nov-85 13:56:35 EST
Article-I.D.: amd.1951
Posted: Thu Nov 21 13:56:35 1985
Date-Received: Sat, 23-Nov-85 01:29:36 EST
References: <>
Reply-To: ching@amd.UUCP (Mike Ching)
Organization: AMD, Santa Clara, CA
Lines: 9

In article <> jlt@meccts.UUCP (James L. Thompson) writes:
>
>  Does anyone know how to determine if the Color Graphics Adapter is
>performing a vertical retrace?

The BIOS tests bit 3 of the 6845 status register (3DAH).  When this
bit is active, the raster is in vertical retrace and the video can
be turned off by clearing bit 3 of the 6845 mode select register
(3D8H).  Reenable video when the update is complete.