Well, look at the pinout of HDMI, and figure it out.
http://en.wikipedia.org/wiki/Hdmi
The video card can tell when an HDMI monitor is connected to the HDMI connector.
One way, is impedance sensing. Impedance sensing in video cards has been
available, on VGA, DVI, HDMI, for a number of years now.
Video_card --------------------> resistive termination in external monitor
TMDS Diff Pairs 100 ohms across each diff pair
So the video card does know, when a monitor is cabled up, to the port.
It can "feel" the 100 ohm load, on each TMDS pair.
This doesn't say anything about the power state though. The communications
are unidirectional on those wires. The video card can't tell whether the
external monitor is powered or not.
(Pin 18 carries +5V to the monitor, such that the SDA/SCL is always operational,
even when the monitor is switched off. Again, the video card can't tell whether
the monitor is using current from this pin or not. If the monitor always drew
current from the pin, then you'd have no state change to detect.)
The "CEC" signal is the only one that is vaguely interesting. CEC was invented
for the sole purpose, of having a communications channel between HDMI devices.
"The CEC allows HDMI devices to control each other when necessary
and allows the user to operate multiple devices with one remote
control handset."
That is used in home theater applications (for autonomous equipment
connected via HDMI). It allows equipment state to be communicated,
such that clicking a remote, turns off all the gear at once.
Someone asks the question here, whether Windows looks for CEC, and the
answer isn't very encouraging for direct hardware support. Apparently
one company sells an adapter, to convert between USB and CEC, as a means
to complete the hardware path (
http://www.rcaware.com/). But whether
that supports all possible, bidirectional communications, isn't clear.
If I had to guess, what they could be doing, is converting from CEC
messages, to IR Blaster protocol on USB.
http://answers.microsoft.com/en-us/...i-cec-in/aeecfe1d-7889-4826-80cb-8ae0a39d67d4
For that to even have a chance of working, the sequence would go like this.
1) Push soft power button on external HDMI monitor.
2) HDMI monitor sends packet over CEC, to computer.
3) HDMI monitor then powers down.
4) Now, it's up to the computer, to decide what to do with
the CEC message it got. Do you want the computer to shut
down, when CEC says to shut off ? Etc. If CEC didn't work
directly, then you'd try the rcaware.com product, and if
the computer was running Media Center, maybe, something would
happen.
I wouldn't expect your average LCD computer monitor, to be
using CEC that way. Maybe a large screen TV set would send stuff
down CEC, but exactly what and when, I can't predict. In a
home theater application, you would hope pressing the power
button on your 60" LCD TV, would turn off the connected
DVR at the same time. And the CEC signal on the HDMI cable,
would be a potential path for such a communications to follow.
*******
It should only take you a couple minutes, to test this on your
laptop plus HDMI based external monitor. Switch off the HDMI
monitor, notice the laptop screen does not light up, the laptop
continues to run. Now, switch on the HDMI monitor, and notice
that nothing has changed, and the session is still running.
If you wanted something more than that, it might take the rcaware.com
device, but even then, if the HDMI monitor doesn't send a packet
on CEC at power down, then there's nothing for the adapter to
work with. So it's very iffy, with regard to getting it to work.
It's more likely to work, with the 60" LCD TV, clicking the
power button on the remote, and that would be able to
trigger a chain of events.
If I was a betting man, I wouldn't make much money betting
a person would get this working.
If you unplug the HDMI cable, *then* the laptop should
re-light the main screen. The impedance sensing generates
"events", if a cable is unplugged, or plugged in.
HTH,
Paul
