Need details how the RSEN bit is asserted in the TFP410 DVI Transmitter.

The RSEN bit will be set when the transmitter detects the active termination on the differential signals at the receiver.  I assume these are DC-coupled transmission lines as this works in every other build in the production line as stated.  As this is appears to be an isolated case, I would suggest the device be returned through the Quality Tracking System to help determine the possible cause of the device failure and corrective action.   I assume replacing the device on the same board corrects any issue seen?

Thank you for your response, however it is entirely unhelpful.

Simply telling me RSEN is set when the transmitter detects the active termination is rather a statement of the obvious.  Please note my initial support request where I said "in detail, how the part does this sensing (ie. what current threshold is required, assuming the RSEN bit is looking at current)".  I even bold faced the part of it to emphasize we require DETAIL how the sensing happens.  Is it a current or voltage sense?  What is the threshold.  How much hysteresis?  How often sampled?  Etc.  I was very clear in my initial comment - that being a specific attempt to avoid exactly this kind of vague response.  I'm discouraged to receive such a bland answer.

To address the remainder of your comments.  The problem manifest only occasionally, so we are not certain this is an isolated case.  We have not replaced the part since it's not at all clear the TFP410 is to blame.  In fact, our end customer more suspects THEIR receiver circuitry.  The support request I've filed here is not a request for debug assistance....it is very specifically a request for information how RSEN asserts.  That is important technical information so we can work to uncover the actual root cause which may very well lay the blame on a circuit element other than the TFP410

Will it be possible to receive precise and detailed information how RSEN operates.  This is information that really should have been in the datasheet to start with.

The RSEN bit will be set when a receiver is detected, the receiver has a 50 ohm termination to 3.3V.  The transmitter swing can anywhere from 400mV to 600mV depending on the settings on the transmit side.   So the TFP410 will detect a receiver when a voltage in the range of 2.7V is detected on the differential inputs.   The specific voltage will depend on the receiver termination voltage level so this is not specified in a datasheet.  

Thank you Undrea - your reply is helpful, but not complete.

You indicate the TFP410 registers a receiver is present when a voltage in the range of 2.7V is detected.  You do not say, but based on the one sentence in the datasheet, I'm presuming it's the TXC+/- diff pair you're referring to.  So if the TFP410 is looking for a voltage in the range of 2.7V.....what signal specifically is it looking for that on?  TXC+, or TXC-, or both?  As I've twice emphasized, to trouble shoot this we need to know EXACTLY how RSEN works.

Using your above guidance, the transmitter can swing somewhere between 400-600mV.  You don't say, but I'll assume you're specifying that as a single ended excusion (since 3.3V - 600mV would yield your guidance of 2.7V).  That would mean the TFP410 could reasonably expect TXC+ or TXC- or both to ALWAYS be 2.7V, or higher.  Is that the RSEN circuit is looking for?  If so, how long an excursion below 2.7V is required before RSEN is deasserted?  Perhaps our customer has noise on their receiver's AVDD input and they may need a spec for how brief a glitch below 2.7V will be trouble.

Once RSEN deasserts, is it free to reassert again immediately - or is there circuitry that latches, or otherwise holds off a reassertion?

Is there voltage hysteresis such that once RSEN deasserts because of a <2.7V detection it's necessary for the voltage to rise to some pre-defined amount beyond 2.7V?  Without hysteresis a receiver with somewhat low AVDD might cause the RSEN detection to oscillate and perhaps malfuntion.  Can you elaborate about hysteresis?

Lastly, though I realize the voltage presented to the TFP410 will certainly depend on the circuit on the receiver side, I fail to understand why that fact makes it not possible to specify the RSEN trip point in the TFP410 datasheet (as you appear to say above).  Perhaps I am fundamentally misunderstanding something - but surely the trip point for the TFP410 is purely a function of circuitry inside the TFP410.  What precisely is that trip point - since above you only ball park it to 2.7V by saying "in the range of 2.7V"?

We have a request into the Design team to provide details. 

Below is the feedback we have received:

RSEN uses TxC+ and TxC- signals for receiver detection.  The exact voltage needed to detect a receiver will require additional simulations which are currently not available, we have taken some lab measurements and the actual DC voltage of detection is typically .9V.  

The RSEN bit will be deasserted on the next clock cycle after the receiver is no longer detected.  Once RSEN deasserts, it is immediately free to reassert.  There is no hysterisis for this circuit.

DC detection voltage of .9V?    .9V measured between what two points?  Are you saying that when the voltage seen on TxC drops below .9V relative to GND RSEN deasserts?  Or is it some differential measurement.  If not, which end of TxC is monitored, TxC+ or TxC-?  Or both where if either misses the threshold RSEN deasserts?  These details are non-trivial and are critical to correctly troubleshoot the malfunctioning assembly - please be exacting in your explanation.

Also, .9V is very different than your previous guidance of 2.7V and having two such different comments doesn't make me feel confident a final correct answer has been reached.  Can you please explain how two very different values have been quoted?