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ad9388a Edid error

Question asked by mbu on Aug 8, 2013
Latest reply on Aug 27, 2013 by mbu

Hi,

 

We have an old design with an ad9388a used as DVI-I input.

Which means we are using both the analog and the digital part of the DVI-I connector.

 

This means we must change the EDID content every time we reconfigure the input between analog/digital.

 

If the DDC lines are accessed from the transmitter while we re-program the EDID, somethings go wrong and

the ad9388 stops to reply on the DDC bus.

It's no use in trying to set the EDID several times, the only way to recover is to reset the ad9388.

In addition am I only able to detect the error from the transmitter side.

 

The hotplug is low-while we change the EDID but some transmitters ignore that and still try to access the DDC bus.

 

See attached scope image of DDC lines and hotplug. The transmitter reads EDID both on negative and positive edge of the hotplug.

 

I have tried to time the re-programming of the EDID in-between the DDC access and it helps but is not really a fix.

 

Is there any (undocumented ?) registers which can give me the state of the EDID I2c-controller and maybe reset it ?

 

I follow the described routine for programming the EDID and it works fine as long as no one

access the DDC lines during EDID re-programming.

 

Martin

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