Seeing what the "sense lines" say about a monitor - How?

Heya folks...

Don't mind me as I ramble - I'll get there eventually, and you might
even find it a fun ride.

I've got the pinouts I need, all the materials, (as salvage, no less!)
the soldering iron, know-how, and time, needed for this little project,
and I've relied heavily on the Technote that discusses the subject
(hw_30.pdf from apple.com - googling "site:apple +sense +monitor" will
put it at the top for you - I forget what the address actually was) in
the process of building myself a cable that does a Mac video-out (male
DB15 2-row connector) to "Generic Windows-box monitor" (female HDB15
3-row connector) conversion. Said cable is being used, right this very
instant, to connect a Gateway EV700 17" monitor to the built-in video
out of my PowerMac 7500-G4/300, the machine I'm typing this message on,
with absolutely flawless results.

Obviously, the "surgery" was successful.

HOWEVER...
On the first build, I hot-swapped the old Apple Multiscan 14" I'd been
using - Everything worked fine. Until I rebooted the system this
morning. (running 9.1, and doing some seriously crufty "down on the
metal" hacking on this beast makes this a wise procedure - I reboot
often as a prophylactic measure whenever I'm "playing in the
sub-basement", which is most of these past few weeks)

The 17" monitor came up with a black screen and an RGB bar pattern
overwritten with a message from the monitor's on-board diagnostics
telling me the monitor was fine, but either there was a problem in the
cable/connections, or the computer wasn't powered up.

This is a non-problem, since I know exactly why this is, and at least
half expected it to happen - I ignored all of the sense-line stuff on
the initial version. It was an intentionally quick-n-dirty first attempt
- Get me synch and RGB, and skip the rest until I find out if I've got
it even partly right. It worked great until reboot because the computer
was convinced there was a 14" Multiscan connected. Since the signals
were compatible, it "just worked". As soon as I rebooted, the computer
"forgot" what it knew about the display, and went to the monitor cable
sense-pins to find out what it needed to know when the restart
commenced. Of course, they were hanging in space, giving a "no monitor
attached" reading. Which meant it never sent synch to the monitor, and
the monitor, seeing no signal, fell into "Nothing to show ya, boss"
mode.

That's when I hit hw_30 to build the sense wiring. I believe I've built
a proper "Hi computer! I'm a 17" multiscan monitor!" response into the
Mac end of the cable using a diode scavenged off (of all things!) an
Apple /// System I/O Board and a snippet of wire. And it's working
exactly as it ought to be. But I want to do some more tinkering...

That's where we get to the real "meat" of this message...

But first:
Please... don't bother telling me I can go out and buy what I'm about to
discuss. I know I can. I also know it'd cost me about $6.50 after tax at
MCC down on Mitchell street, next door to Lambert's. I also know I've
got way more than plenty to cover the cost of both the drive down to get
it, and the device itself, sitting right here in my pocket. But this is
one of those "I'm gonna build it instead of buying it because I feel
like it and I'll learn something in the process" projects that I have
zero interest in spending anything but time, solder, and brainpower on.

Now, on with our main course...
Knowing what you now know from wading through this epic up to this
point, I'm wanting some software - Software I'm perfectly able and
willing to code, if I get a couple of tidbits of information that I
can't seem to find. I'm probably feeding google the wrong search info.

Critical one: Is there, under 9.1 running on a 7500-G4/300, a way to
find out what the monitor cable will say to the computer when the
computer asks "What kind of monitor are you connected to?" at startup?

Second tidbit: How to interpret any such responses. I expect they'll be
encoded somehow - perhaps a bitfield, since there are only three pins,
and the extended sense scheme can only be extended so far. IE, if a
query is done, and the result comes back as the value 0x2F - What'd it
just tell me about the monitor?

I'd like to put together a switchable unit to let me change the response
at will - This reboot, I want the monitor to be a 21" 68Hz fixed-scan
monochrome. Next reboot, it needs to look like a _________, so I'll
set the switches to _______.

Obviously, to figure out how I need to set the switches, I need to be
able to see what changing the response looks like at the "what are you?"
stage.

Any help to be had?

--
Don Bruder - dakidd RemoveThis @sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details.

In article <mZ_Hd.3044$m31.38651@typhoon.sonic.net>, Don Bruder <dakidd.DeleteThis@sonic.net> writes:
[...]
>Now, on with our main course...
>Knowing what you now know from wading through this epic up to this
>point, I'm wanting some software - Software I'm perfectly able and
>willing to code, if I get a couple of tidbits of information that I
>can't seem to find. I'm probably feeding google the wrong search info.
>
>Critical one: Is there, under 9.1 running on a 7500-G4/300, a way to
>find out what the monitor cable will say to the computer when the
>computer asks "What kind of monitor are you connected to?" at startup?
>
>Second tidbit: How to interpret any such responses. I expect they'll be
>encoded somehow - perhaps a bitfield, since there are only three pins,
>and the extended sense scheme can only be extended so far. IE, if a
>query is done, and the result comes back as the value 0x2F - What'd it
>just tell me about the monitor?
>
>I'd like to put together a switchable unit to let me change the response
>at will - This reboot, I want the monitor to be a 21" 68Hz fixed-scan
>monochrome. Next reboot, it needs to look like a _________, so I'll
>set the switches to _______.
>
>Obviously, to figure out how I need to set the switches, I need to be
>able to see what changing the response looks like at the "what are you?"
>stage.
>
>Any help to be had?

I don't think you need the software. Why not use the Mac OS as such? As soon as
the Mac "recognizes" a monitor it will adjuste the corresponding control panel
"Monitors". Once you open this one it will only list the resolutions your
"monitor" is capable of. On the other hand this proves that it is possible to
get this data from within a program. Otherwise the control panel couldn't
perform how it actually does.

Regards,
Christoph Gartmann

--
Max-Planck-Institut fuer Phone : +49-761-5108-464 Fax: -452
Immunbiologie
Postfach 1169 Internet: gartmann@immunbio dot mpg dot de
D-79011 Freiburg, Germany
http://www.immunbio.mpg.de/home/menue.html