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AD9984 i2c, reading only 0's

Question asked by prrole on Dec 29, 2014
Latest reply on Jan 15, 2015 by analogman

Hi, I experience some issues bringing up an ad9984.  I've made a prototype PCB for it, and the only thing not hooked up is the REFLO/REFHI and the filter capacitors as I didn't have them handy - hopefully it's not the source of my issues.

 

When doing an i2cdetect, it shows up as 0x4c, as it should, and I've put a 10k pulldown on the vsout/A0 pin.

 

The issue is that the chip only replies with 0, like here where I try to get chip revision:

 

ad9984.png

I'm reading this from a raspberry PI with the wiringpi library, screenshot is a capture from a saleae logic analyzer.  No matter which register I query, I get only 0's back. 

 

I CAN however write correctly, when hooked up to a scope I can for example flip the vertical sync polarity and observe correct behavior - still, reading back the same register yields only 0.

 

To rule out any i2c master issues, I hooked up a TI TVP7002 chip, and it works as expected:

tvp7002.png

Further to (minimize risk of)/rule out a bad chip, I assembled my second AD9984 to an identical second board - and behavior is the same.

 

SCL is set to 100khz.

 

Any ideas what the issue can be or how to proceed debugging?

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