Path: utzoo!attcan!uunet!lll-winken!sol.ctr.columbia.edu!cica!iuvax!daemon
From: commgrp@silver.ucs.indiana.edu (BACS Data Communications Group)
Newsgroups: sci.electronics
Subject: Re: VGA mode sensing
Message-ID: <70179@iuvax.cs.indiana.edu>
Date: 6 Nov 90 16:08:10 GMT
Sender: daemon@iuvax.cs.indiana.edu
Lines: 37

agodwin@acorn.co.uk (Adrian Godwin) writes:

>I'm trying to connect a Mitsubishu high-resolution monitor (32kHz, 
>BNC inputs, no concessions at all to VGA standards, which it pre-
>dates) to the VGA port on a Compaq 386.

>It works fairly well, but only in monochrome. The Compaq's self-
>determining setup detects a Mono VGA monitor, and won't do colours.

>I've found some references to the possibility that the loading on the 
>RGB signals are used to configure the monitor type, and the ID bits 
>on the VGA connector (pins 11, 12, possibly pin 4) are ignored.

>Does anyone know for sure what the rules are ? 
>What about SVGA - is that monitor capability sensed automatically too ?

I don't know how Compaq does it, but here is the connector pinout of 
an IBM color VGA connector (model 8513):

You might try various combinations of open and ground on pins 11 and 12.

1  Red video                            9 Reserved
2  Green video                         10 Ground
3  Blue video                          11 Monitor sense (ground)
4  Reserved                            12 Monitor sense (open)  
5  Self test                           13 Horizontal synch
6  Red video return (coax shield)      14 Vertical synch
7  Green "     "       "     "         15 Reserved
8  Blue  "     "       "     "

On IBM monitors, the "self test" line causes a white raster on the 
screen when the cable is disconnected.  The video signals are 
terminated at 75 ohms.

--

Frank Reid     reid@ucs.indiana.edu