Path: utzoo!attcan!uunet!jarthur!elroy.jpl.nasa.gov!usc!apple!portal!cup.portal.com!Nandu
From: Nandu@cup.portal.com (Narendra J Kulkarni)
Newsgroups: sci.electronics
Subject: Re: VGA mode sensing
Message-ID: <35638@cup.portal.com>
Date: 6 Nov 90 01:48:28 GMT
References: <3943@acorn.co.uk>
Organization: The Portal System (TM)
Lines: 9

Most of the clone VGA cards ignore the moniter ID bits, they sense moniter
type, mono/color/or no moniter by load on the RGB lines, the RAMDAC output
of the VGA DAC is a current output, usually the VGA card has a 75 ohm ter
minating resistance and the moniter has 75 ohm on RGB lines, the VGA card
senses the voltage developed on the RGB lines by means of a comparator and
detects the moniter, for mono moniter only one line usually green has 75 ohm
for color all three have 75 ohm, your problem may be that the moniter does no
t have terminating resistor, or something is not hooked right, make sure that
your RGB return lines are connected to RGB return on VGA  15 pin connector