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ADS1242 DRDY (DATA READY) question

DannyEllen
Intellectual 685 points

Other Parts Discussed in Thread: ADS1242

Hi,

I am trying to read the ADS1242 ADC with RDATA at my own pace.
The ADS1242 datasheet states:

"DRDY goes LOW when a new data word is available in the DOR register.
It is reset HIGH when a read operation from the data register is complete."

I put a probe on the pin. I expected the DRDY to be high most of the
time (It should go low after I send the RDATA when data is ready 
and go high again after SPI read.
But I always see the DRDY pumping at a 30.3 Hz frequency with
a high pulse of about 32 uSec. 

I tried sending STOPC but that did not change DRDY behavior.

What am I doing wrong? 

Best regards,

Danny

  • 0
    TI__Guru**** 182721 points

    Hi Danny,

    Happy New Year to you!  Can you send us a screen capture of your SPI interface?  The ADS1242 does not really have a single shot or 'pulse convert' operating mode.  By the description above, it sounds like you are using the device with a 4.9MHz oscillator and the SPEED+DR bits set to zero.  If you simply let the device convert (without attempting to read data) you should see the DRDY pulse high at the rate of ~30Hz.  The high period should be about 4 periods of the 4.9MHz oscillator (~816ns).

  • 0 in reply to Tom Hendrick
    Intellectual 685 points

    Hi Tom, 
    Happy new year to you too, and thanks for answering on the holiday.
    Yes I am using a 4.9 MHz clock and all registers are in their default values.
    With no software working I get 31.6 us (not 816 ns) DRDY pulse width at 30.12 Hz rate.
    I attached the DRDY wave-forms right after power on without software running.
    It is a bit difficult access to probe the SPI lines, but the results I read with software at this early 
    project commissioning stage seem reasonable. (my SPI clock is 3.75Mhz using a TI 320F28035).

     

    Do you think that somthing is out of the ordinary with my electronics?

    Cheers,

    Danny

  • 0 in reply to DannyEllen
    TI__Guru** 113765 points

    Danny,

    This looks correct.  The update for DRDY will pulse even if in STOPC mode.  If you read the data, DRDY should go back high until the next set of data becomes available at which time it will go low again. 

    In short, DRDY will go high when you read the results and stay high until the next conversion is available.  If you don't read the data, the you will see DRDY stay low and then pulse indicating new data is available.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Intellectual 685 points

    Thanks Bob,

    Yes you are right, Now everything works !!!

    Best regards,

    Danny