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ADS1114: Set to assert conversion ready pulse after every 2 conversions, but asserts every single conversion

Part Number: ADS1114

Hi, I'm having trouble figuring out why I can't get the ADS1114 to generate a conversion ready flag after every 2nd conversion while in continuous conversion mode.  I am writing the configuration and hi/lo threshold registers correctly, as far as I can tell.  Right now it generates a conversion ready flag after every single conversion.  Including scope shots of the config register write and hi/low threshold register writes just in case there's something I'm missing.  I'm writing an 0x42E5 to the config register for continuous conversion mode, 860 sps - screen grab below.  I'm also writing 0x7FFF to the lo threshold register and 0x8000 to the hi threshold register to activate the RDY pulse.  

  • Jared,

    The way you have it set up is correct. Setting the high threshold register below the low threshold register should get the ALERT/RDY pin to trigger for each conversion. Can you show the ALERT/RDY pulse on the scope? You should see something like Figure 29 of the datasheet:

    I would note that this is a narrow 8us high pulse, with a period of 1.2ms. It might be hard to capture pulses depending on the resolution of the scope. Get the shot and put it in a follow-up post.

    Joseph Wu

  • Hi Joseph - thanks for the quick response.  Yes, I can see the pulse, though I have it inverted (active low), and it is repeated at 1.22ms, which equates to a 819 sps rate (within the +/- 10% of 860 sps per the datasheet).  For every 2nd conversion, I would expect to see it at closer to 2.3ms.

  • Jared,

    I'm sorry, but I totally misunderstood your post. I'd forgotten this device has a a comparator that can be set to trip after a set number of conversions (1, 2, and 4).

    I believe that what you are seeing is that the comparator still sees that the previous two conversions are outside the threshold limit and sets the ALERT/RDY high. The latching comparator function just sets the ALERT/RDY high when it's not read out, it doesn't clear the count of the previous conversions that are outside the limits.

    Joseph Wu