VGA Monitor Identification Bits?

[webpa]

I give up: How does a Sony (FX-140) notebook recognize the presence of
an external (VGA/SVGA) monitor? Many Google hits on the topic provide
monitor ID bit identifications...and variations thereon. But NONE of
them seem to work. That is: Grounding the indicated pins, in all
possible combinations, does not cue the computer that a monitor is
connected. It cannot be that the FX-140 requires active communication
with a monitor, because the computer recognizes ANY connected monitor
(have tried 5) whether they are powered or not.

Any hints? Diodes between pins...resistors...holy water?

 

[Adrian C]

Any hints? Diodes between pins...resistors...holy water?

Resistors, 75 ohm on each output R, G & B line to ground.

 

[ciscodsl]

Any hints?

If the monitor is of the newer type (made in say about the last 13
years or so) it will have a pair of serial interface wires in the
monitor cable that allow the computer, via the VGA Video BIOS, to
access a 128 byte or 256 byte serial eeprom memory in the monitor to
determine specific information about the monitor. This memory is known
as the EDID and the typical access is via the I2C type protocol
through the video adapter board.

The EDID in monitors of this era replace the old two or three "pins to
ground" monitor ID bits that were used in the early part of the '90s.
In the days after the multi-sync monitors were introduced and we
started to see a dizzying array of video formats appear the monitor ID
system rapidly became useless and thus the development of the EDID
system.

ciscodsl

 

[Meat Plow]

I give up: How does a Sony (FX-140) notebook recognize the presence of
an external (VGA/SVGA) monitor? Many Google hits on the topic provide
monitor ID bit identifications...and variations thereon. But NONE of
them seem to work. That is: Grounding the indicated pins, in all
possible combinations, does not cue the computer that a monitor is
connected. It cannot be that the FX-140 requires active communication
with a monitor, because the computer recognizes ANY connected monitor
(have tried 5) whether they are powered or not.

Any hints? Diodes between pins...resistors...holy water?

Impedance change.

 

[Franc Zabkar]

I give up: How does a Sony (FX-140) notebook recognize the presence of
an external (VGA/SVGA) monitor? Many Google hits on the topic provide
monitor ID bit identifications...and variations thereon. But NONE of
them seem to work. That is: Grounding the indicated pins, in all
possible combinations, does not cue the computer that a monitor is
connected. It cannot be that the FX-140 requires active communication
with a monitor, because the computer recognizes ANY connected monitor
(have tried 5) whether they are powered or not.

Any hints? Diodes between pins...resistors...holy water?

If the notebook recognises that a monitor is present but cannot
identify its capabilities, then it is probably sensing the 75 ohm RGB
terminations. If the notebook can ID the model, make, and refresh
rates, then it is reading the monitor's EDID EEPROM. Note that it is
the notebook's graphics subsystem which provides the power for the
monitor's EEPROM, not the monitor.

See the DDC info here:
http://pinouts.ru/Video/VGA15_pinout.shtml

The EDID data block will appear in your registry.

I have also managed to read a monitor's EDID EEPROM using my device
programmer. I made a VGA DB15-to-DIP8 adapter cable and told the
programmer that it was connected to an Atmel AT24C21 EEPROM which has
a "DDC1/ DDC2 Interface Compliant for Monitor Identification".

http://www.atmel.com/dyn/resources/prod_documents/doc0405.pdf

- Franc Zabkar

 

[webpa]

If the notebook recognises that a monitor is present but cannot
identify its capabilities, then it is probably sensing the 75 ohm RGB
terminations. If the notebook can ID the model, make, and refresh
rates, then it is reading the monitor's EDID EEPROM. Note that it is
the notebook's graphics subsystem which provides the power for the
monitor's EEPROM, not the monitor.

See the DDC info here:
http://pinouts.ru/Video/VGA15_pinout.shtml

The EDID data block will appear in your registry.

I have also managed to read a monitor's EDID EEPROM using my device
programmer. I made a VGA DB15-to-DIP8 adapter cable and told the
programmer that it was connected to an Atmel AT24C21 EEPROM which has
a "DDC1/ DDC2 Interface Compliant for Monitor Identification".

http://www.atmel.com/dyn/resources/prod_documents/doc0405.pdf

- Franc Zabkar

OK. I guess I was not clear enough: I want my computer to think a
monitor is attached to its VGA port when a monitor is not connected.
This is necessary because I want to be able to turn the computer's LCD
"OFF" for extended periods of time while it is recording streaming
audio. (The APM will ***NOT*** do this...if an app is active, the APM
will not turn off internal LCD, not matter what). The FN+F7 cycle
will not work unless the computer senses a monitor attached to the VGA/
SVGA connector.

BTW...None of the suggestions so far have provided a useful answer.

I'm now gravitating to buying a junk CRT monitor and stuffing the
interface card into a plastic bag at the end of a short VGA cable.

Bur surely....

 

[msg]

webpa wrote:

OK. I guess I was not clear enough: I want my computer to think a
monitor is attached to its VGA port when a monitor is not connected.
This is necessary because I want to be able to turn the computer's LCD
"OFF" for extended periods of time while it is recording streaming
audio. (The APM will ***NOT*** do this...if an app is active, the APM
will not turn off internal LCD, not matter what). The FN+F7 cycle
will not work unless the computer senses a monitor attached to the VGA/
SVGA connector.

BTW...None of the suggestions so far have provided a useful answer.

I'm now gravitating to buying a junk CRT monitor and stuffing the
interface card into a plastic bag at the end of a short VGA cable.

If it were me, I would just make an EDID circuit (as described in some
of the previous replies) and attach that to the vga connector. Perhaps
some high-end KVM switches also emulate a monitor and provide necessary
IDs at the connector.

Regards,

Michael

 

[Tim]

If the notebook recognises that a monitor is present but cannot
identify its capabilities, then it is probably sensing the 75 ohm RGB
terminations. If the notebook can ID the model, make, and refresh
rates, then it is reading the monitor's EDID EEPROM. Note that it is
the notebook's graphics subsystem which provides the power for the
monitor's EEPROM, not the monitor.

See the DDC info here:
http://pinouts.ru/Video/VGA15_pinout.shtml

The EDID data block will appear in your registry.

I have also managed to read a monitor's EDID EEPROM using my device
programmer. I made a VGA DB15-to-DIP8 adapter cable and told the
programmer that it was connected to an Atmel AT24C21 EEPROM which has
a "DDC1/ DDC2 Interface Compliant for Monitor Identification".

http://www.atmel.com/dyn/resources/prod_documents/doc0405.pdf

- Franc Zabkar

OK, that sounds kinda fun. I'm going to look into that if my programmer
has the ability to program that Eeprom...

Thanks for the info Franc,

- Tim -
--

 

[Franc Zabkar]

OK. I guess I was not clear enough: I want my computer to think a
monitor is attached to its VGA port when a monitor is not connected.

Adrian's suggestion should work. There are some PC BIOSes that will
fail to POST if they do not detect 75 ohm terminations on the graphics
card's RGB outputs. In this case I have managed to fool them by
connecting 75 ohm terminations between each of the RGB outputs and
their corresponding signal returns.

- Franc Zabkar

 

[msg]

OK, that sounds kinda fun. I'm going to look into that if my programmer
has the ability to program that Eeprom...

Wouldn't any easy solution be to scrap an unneeded monitor and
recover the already programmed device from it and wire up a dongle for
the vga connector?

Regards,

Michael

 

[Andy Cuffe]

OK. I guess I was not clear enough: I want my computer to think a
monitor is attached to its VGA port when a monitor is not connected.
This is necessary because I want to be able to turn the computer's LCD
"OFF" for extended periods of time while it is recording streaming
audio. (The APM will ***NOT*** do this...if an app is active, the APM
will not turn off internal LCD, not matter what). The FN+F7 cycle
will not work unless the computer senses a monitor attached to the VGA/
SVGA connector.

BTW...None of the suggestions so far have provided a useful answer.

I'm now gravitating to buying a junk CRT monitor and stuffing the
interface card into a plastic bag at the end of a short VGA cable.

Bur surely....

It's probably just looking for a 75 ohm load on one, or more, of the
RGB output pins. It's unlikely that they designed the laptop so that
it would only work with a monitor that had ID pins, or EDID. Many
high end monitors use BNC inputs, and there is no ID, or EDID on a VGA
to BNC cable. Simply make a terminator dongle out of a VGA connector.
Andy Cuffe

[email protected]

 

[webpa]

It's probably just looking for a 75 ohm load on one, or more, of the
RGB output pins. It's unlikely that they designed the laptop so that
it would only work with a monitor that had ID pins, or EDID. Many
high end monitors use BNC inputs, and there is no ID, or EDID on a VGA
to BNC cable. Simply make a terminator dongle out of a VGA connector.
Andy Cuffe

[email protected]

Thanks to all! 100 ohm resistors from R, G, & B to their returns did
the job. Computer now thinks there is a monitor attached.