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adv7611 i2c failures.

Question asked by dmerillat on Jun 29, 2015
Latest reply on Jun 30, 2015 by mattp

I'm getting unusual responses from the 7611 on my i2c bus (control port, not HDMI port). 

 

The I2C itself works with the other chip on the board (a clock generator) and those traces look exactly like you would expect for I2C.  When addressing the 7611 the 'ack' is a partial rise to 675mv, followed by a slow rise to 1.375v, before a release to 3.3 and a downspike.  My micro is not accepting that final ack either, though the scope's logic thinks it is ok.

 

The second piece of information is the rolloff on the rising edges - in this screenshot, we had a very weak pullup - either 50 or 100k.  It was an experiment, since the on the normal 4.5k value the 7611 did not respond to its address at all.

 

The third piece is that it fails to respond to commands after specific register settings - powerup and disable tristate are the most reliable triggers.

 

Other bits - reset is held until the all the power planes are up and clean, then we delay 10ms after releasing the 7611 from reset before addressing it via i2c.

 

It looks like a power problem, but since all the voltage rails are correct and clean on each input pin, I would guess the ground pad on the bottom. Has anyone seen a trace like this so we have some other ideas what to check?

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