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ADC128D818: Setting up zero limit

Dmitry Nezhevenko
Prodigy 90 points

Part Number: ADC128D818

Hi,

I'm trying to use ADC128D818 to monitor input voltage. One of my inputs is expected to be zero (or near zero, for example <=0.2V). Could you please suggest, is it possible to configure Limit Registers such way that it'll trigger interrupt only when voltage is less than certain value.

Basically I need to just ignore LOW register. Currently this input is just shorted to the GND pin. Also I can confirm that reading output register returns always 0.

But even if I write LOW=0x00 and HIGH=0xFF limit (which looks like 'anything is ok' for me), I'm still getting interrupt and ISR has '1' for this input.

Any suggestions?

  • 0
    Prodigy 90 points
    Sorry. forgot to add. I'm using ADC in MODE 0/1 (single ended inputs). Also powering this input with low voltage (that ADC converts to 12bit value of 0x001) stops these interrupts.
  • 0
    TI__Guru**** 183271 points
    Hi Dmitry,

    I don't see any obvious way to accomplish this when reading through the ADC128D818 datasheet. Let me do a little research and I'll get back to you as soon as possible.
  • 0 in reply to Dmitry Nezhevenko
    TI__Guru**** 183271 points
    Hi Dmitry,

    Is simply masking that interrupt an option? Also, I'm not sure I understand your second comment - are you saying that programming the lower limit to 0x00 and you provide an input that corresponds to 0x001, the interrupt does not trip? That would make some sense since you are technically over the limit boundary.
  • 0 in reply to Tom Hendrick
    Prodigy 90 points

    Hi. I want to program lower limit as exactly '0x00' (because I don't care about LOW for this input). My expectation was that ADC chip will assume that '0' is ok and will trigger interrupt only when voltage will became > HIGH. And basically I need just to be notified when voltage will became > HIGH.

    So for testing purposes So I programmed ADC like LOW = 0x00, HIGH = 0x50. And getting interrupts when input is shorted to GND (0.0v). Connecting IN pin to some very low voltage stops these interrupts.

    Basically it looks like ADC128D818 itself checks that IN > LOW (while I was expecting that it's IN >= LOW). Btw I can't find confirmation for this information in datasheet.

    In any case I've decided to just mask interrupt for this particular input for now and replace it with simply polling. Later I'll try to add some small constant voltage to this input.

  • 0 in reply to Dmitry Nezhevenko
    TI__Guru**** 183271 points
    Hi Dmitry,

    The interrupt triggers when the voltage reading > the voltage high limit or ≤ the voltage low limit. In the scenario you described, the INT should fire at 0x51 on the high side and 0x00 on the low side.
  • 0 in reply to Tom Hendrick
    Prodigy 90 points
    Thanks!.
    My assumption was (Vin > high) || (Vin < LOW).