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ADS7924: unexpected i2c behavior

Art Mecina
Genius 16505 points
Part Number: ADS7924

Hello Guys,

Our customer is having some unexpected i2c behavior with a ADS7924IRTER.
It is supposed to respond to the address of 0x48 but he is only getting acks at 0x28.
it is only responding with acks at address 0x28.
See attached.

Thanks!

Art

  • 0
    TI__Mastermind 24940 points

    Hello Art,

    I am not sure what setting the logic is using, but the device uses the rising and falling edge to read data. refer to the image below from the datasheet. 

    Looking at the scope shot you provided, I would read the first frame as: 0101 0000 - x50h, I am not sure why the logic is showing it as x28

    But either way, the device is not being communicated with correctly. 

    The first frame should look like the image shown below, the first bit should be high = 10010000 - x90h

    Regards

    Cynthia

  • 0 in reply to Cynthia
    TI__Genius 16505 points

    Thanks for looking into this Cynthia!

    His A0 is connected to ground. Logic was showing x28 because it was in a mode that decodes and displays the 7 highest bits.

    Should he have seen an ACK here?

    Art

  • 0 in reply to Art Mecina
    TI__Mastermind 24940 points

    Art,

    If there is nothing else on the bus, you should not have seen an ACK. But if there are other devices, then those could be responding to the commands. 

    With A0 pin grounded, then the device address is shown below.

    The first bit should be high in the address frame, in the Logic analyzer it shows that it is not.

    Regards

    Cynthia

  • 0 in reply to Cynthia
    TI__Genius 16505 points

    Thanks Cynthia!

    I will close this ticket now. Apparently the issue is device related. When the parts were replaced with those coming from a different distributor, the circuit works.

    Best regards,

    Art