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ADV7850 - Floating DDC line on output blocking analog video from passing?

Question asked by JeremyM on Apr 26, 2013
Latest reply on May 1, 2013 by JeremyM

Our current usage of the ADV7850 is for the analog input only which feeds an always connected ADV7623 via HDMI downstream.  The HPD of the downstream 7623 is pulled high to always indicate that the upstream 7850 is present, but the DDC lines between the two devices are floating (we do not need the 7850 to read the EDID from the downstream 7623 and will always have HDCP disabled).

 

The datasheet for the 7850 states that it internally controls the output TMDS clock - since we have the DDC lines floating, EDID writes and HDCP will of course fail.  We have disabled HDCP and have a workaround for the EDID on the 7850, but are not getting any video out of the 7850 with valid analog input.  We see the RX end of the 7850 properly decode the incoming signal and setup seems to occur properly on the TX end of the 7850, but no video. 

 

Question: We are wondering if the internal state machine of the 7850 (which takes care of EDID reads and progresses through HDCP authentication) is blocking TMDS output because we don't have the DDC lines connected and are spoofing the EDID?

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