DVI-D and Analog sync pulses

'noon all,
I need to be able to get hold of the analog vertical sync pulse from a
DVI-i connector.
No problem in Analog mode, all the lines are waggling away nicely
However I need to actually run a DVI-D DMD projector from the port,
and be able to
sync something else to it.
My cunning plan was to use the vertical sync as a 'start of frame'
pluse that I can add
some noddy electronics to in order to do the job.
However (theres always a gotca isnt there?):

When I plug the DVI-D device in it seems the analog lines get turned
off...(arrgh!)

Does anyone know if this is a 'normal' thing, or just from this
perticular graphics card
(Nvidia 9800 GT chipset)? The only other card I have here is also an
NVidia chipset (older),
and it exibits the same symptoms.

Any cunning plans to sync without this signal would be grafefully
accepted

cheers

Dave

wrote:
'noon all,
I need to be able to get hold of the analog vertical sync pulse from a
DVI-i connector.
No problem in Analog mode, all the lines are waggling away nicely
However I need to actually run a DVI-D DMD projector from the port,
and be able to
sync something else to it.
My cunning plan was to use the vertical sync as a 'start of frame'
pluse that I can add
some noddy electronics to in order to do the job.
However (theres always a gotca isnt there?):

When I plug the DVI-D device in it seems the analog lines get turned
off...(arrgh!)

Does anyone know if this is a 'normal' thing, or just from this
perticular graphics card
(Nvidia 9800 GT chipset)? The only other card I have here is also an
NVidia chipset (older),
and it exibits the same symptoms.

Any cunning plans to sync without this signal would be grafefully
accepted

cheers

Dave

My first experiment would be, to make sure the RGB analog signals
have 75 ohm terminations present, while the DVI-D is being used.
That is one indication that a VGA plug is present. I'm less sure
about what the conditions should be on HV. Some documentation
seems to indicate they're not terminated, so I don't know if
the pad drivers for those, would work with a 75 ohm load on them
or not. My old Sony Trinitron, used 75 ohm cabling for all the
signals, which is why I'm not sure. (Ordinary VGA cabling seems
to treat H and V, less well, than R, G, and B.)

I have a VGA 15 pin connector, on which I've placed three 75 ohm
resistors. The 75 ohm resistors go to their respective ground
returns. When I plug that dongle into my video card (VGA connector),
the video card thinks a second monitor is present (even though no EDID
info is available to the video card and driver). So just the
presence of 75 ohms is enough to convince it that a monitor is
connected.

Now, would that be enough to convince the driver software, to
leave signals on both digital and analog of the same
connector ? Probably not.

*******

You could probably pick sync off the DVI-D, if it wasn't for
HDCP. Depending on the resolution, the DVI-D link could be
encrypted, or in plain text. If it was plain text, a second
decoding device might be able to find sync.

This Chrontel transmitter accepts H,V, or DE. As far as I know,
DE identifies the "valid" data clock cycles.

http://www.chrontel.com/pdf/7301ds.pdf

This Silicon Image part, shows an unencrypted solution for receive.

http://www.siliconimage.com/products...ct.aspx?pid=12

http://www.siliconimage.com/docs/SiI-DS-0096.pdf

A DVI splitter can be used to make a copy of the original signal.
(This is better than some passive cable solution, which may be
doing horrors to the differential signals.)

http://www.gefen.com/kvm/dproduct.jsp?prod_id=1403

You can then get a DVI to VGA box, and from that, your
sync signals.

http://www.gefen.com/kvm/dproduct.jsp?prod_id=1209

If content protection is involved, I don't know enough about
that, as to what resolutions will work using that idea. We
can thank the movie industry for making this more difficult
than it has to be.

Good luck,
Paul

On 7 May, 19:46, Paul wrote:
wrote:
'noon all,
I need to be able to get hold of the analog vertical sync pulse from a
DVI-i connector.
No problem in Analog mode, all the lines are waggling away nicely
However I need to actually run a DVI-D DMD projector from the port,
and be able to
sync something else to it.
My cunning plan was to use the vertical sync as a 'start of frame'
pluse that I can add
some noddy electronics to in order to do the job.
However (theres always a gotca isnt there?):

When I plug the DVI-D device in it seems the analog lines get turned
off...(arrgh!)

Does anyone know if this is a 'normal' thing, or just from this
perticular graphics card
(Nvidia 9800 GT chipset)? The only other card I have here is also an
NVidia chipset (older),
and it exibits the same symptoms.

Any cunning plans to sync without this signal would be grafefully
accepted

cheers

Dave

My first experiment would be, to make sure the RGB analog signals
have 75 ohm terminations present, while the DVI-D is being used.
That is one indication that a VGA plug is present. I'm less sure
about what the conditions should be on HV. Some documentation
seems to indicate they're not terminated, so I don't know if
the pad drivers for those, would work with a 75 ohm load on them
or not. My old Sony Trinitron, used 75 ohm cabling for all the
signals, which is why I'm not sure. (Ordinary VGA cabling seems
to treat H and V, less well, than R, G, and B.)

I have a VGA 15 pin connector, on which I've placed three 75 ohm
resistors. The 75 ohm resistors go to their respective ground
returns. When I plug that dongle into my video card (VGA connector),
the video card thinks a second monitor is present (even though no EDID
info is available to the video card and driver). So just the
presence of 75 ohms is enough to convince it that a monitor is
connected.

Now, would that be enough to convince the driver software, to
leave signals on both digital and analog of the same
connector ? Probably not.

*******

You could probably pick sync off the DVI-D, if it wasn't for
HDCP. Depending on the resolution, the DVI-D link could be
encrypted, or in plain text. If it was plain text, a second
decoding device might be able to find sync.

This Chrontel transmitter accepts H,V, or DE. As far as I know,
DE identifies the "valid" data clock cycles.

http://www.chrontel.com/pdf/7301ds.pdf

This Silicon Image part, shows an unencrypted solution for receive.

http://www.siliconimage.com/products...ct.aspx?pid=12

http://www.siliconimage.com/docs/SiI-DS-0096.pdf

A DVI splitter can be used to make a copy of the original signal.
(This is better than some passive cable solution, which may be
doing horrors to the differential signals.)

http://www.gefen.com/kvm/dproduct.jsp?prod_id=1403

You can then get a DVI to VGA box, and from that, your
sync signals.

http://www.gefen.com/kvm/dproduct.jsp?prod_id=1209

If content protection is involved, I don't know enough about
that, as to what resolutions will work using that idea. We
can thank the movie industry for making this more difficult
than it has to be.

Good luck,
* * Paul

Thanks for the ideas
Ill give them a go and post results.

Dave