Subject: Re: Big Screen
To: Michael J. Oehler <macbsd-general@NetBSD.ORG,>
From: Henry B. Hotz <>
List: macbsd-general
Date: 02/21/1995 16:46:22
>-- DOES anyone know what these sort of adaptors do? --
>Do they ground certain pins or strobe a signal on the
>Mac's DB15  video plug? After looking at the pin out specification,
>all pins where assigned to either RGB (3), RGB ground (3), H & V synch (2),
>composite (1), some no connects (3), and misc. grounds (3). How's it work?

I'm operating from memory, but here goes:  I assure you there are three
lines that are used for resolution sensing and I don't think there are any
unused pins on the connector.  Nowadays the sense lines can be connected
together with either wire or diodes (either orientation) in any combination
to give you a fair number of possibilities.  The original standard only
used wire and defined 640X480 color, ditto monochrome, PAL, NTSC, and maybe
a couple of others like full page monochrome and two page color.

What these adaptor plugs do (besides connecting RGB&ground to the correct
pins on the VGA connector) is connect the appropriate wires/diodes amoung
the three sense pins.  The ones I have seen have the different
configurations labeled as to what resolution they are supposed to represent
so you usually don't need to worry about it beyond wondering what
resolutions are supported by the Apple hardware you have.

Henry B. Hotz

The opinions expressed are my own,
not Loral's, and not Librascope's.