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ADS 1148 "DRDY problem"

Fabio Balboni
Prodigy 60 points

Other Parts Discussed in Thread: ADS1148

Hi all,

I am using ADS1148 to read analog data. 

I set up registers and read their content. (I configured the register SYS0-System Control Register 0 for 2KSPS)
However, when I try to convert I would expect the DRDY signal normally high, however I see normally low ...
I'm trying to follow the example of the datasheet page 50.
Where am I doing wrong?


RED .............. SCLK
GREEN ........ DIN (MOSI)
BLUE ........... DOUT (MISO)
YELLOW ..... DRDY

thanks,

Fabio

  • 0
    TI__Guru** 113765 points

    Hi Fabio,

    DRDY signals when new conversion results are available.  This is a transition from high to low.  If you do not read the results between conversion periods, you will see that DRDY remains low, and a pulse will occur that signals the end of conversion and an update period of the new data results to the results register.  What you are seeing is normal behavior.  If you send an SCLK between conversions you will see that DRDY goes high as you expect.  In this case you will not see the pulse, just the transition from high to low.

    I do have one suggestion.  It appears that you are leaving MISO and MOSI float.  I would suggest using a weak pull-up on these lines using 100k ohm resistors so that the CMOS inputs are not floating.  This eliminates the potential for the input gate from inadvertantly drawing excessive current.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 60 points

    thank you very much for your suggestion, so as soon as I try.

    Now I have a problem. I turn on the device and sampling times an n-channel I get the correct count. Other times I turn on the device and sampling the same channel I always read "7FFF".
    What could it be?

    thanks
    fabio

  • 0 in reply to Fabio Balboni
    TI__Guru** 113765 points

    Hi Fabio,

    The reading you get with 0x7FF is positive full-scale.  You might get this from a connection issue, a missing reference, or incorrect register settings.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 60 points

    thank you Bob ^___^

    Fabio