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Original question:

TCA6408 & PCA9534 Interrupt issue

PCA9535: interrupt initial value

Mark Huang44
Prodigy 130 points
Part Number: PCA9535
Other Parts Discussed in Thread: TCA9535

I assume the initial value of interrupt pin is High-Z due to open-drain.

However I found it keeps low during power off to power on.

I didn't connect anything to I/O and I2C on PCA9535.

Just have below circuit.

- 3.3V on VCC

- grounding on GND

- use 10K ohm to pull-up interrupt pin

My question:

- Is it correct that "the initial value of interrupt pin keeps low during power off to power on" ?

- If so, How can I modify the initial value of interrupt pin to HIGH-Z ?

  • 0
    TI__Mastermind 49110 points

    Hey Mark,

    Can you tie the I/O pins of the device to GND or Vcc with a resistor? At the moment, you have the I/O pins floating which may cause this behavior.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 130 points

    Hi Bobby,

    Thanks for your reply.

    However it is the same after I connect all IO to GND.

    Even I used normal trigger of scope, INT# has no any high period during power off to on.

    Please refer to below picture.

    Thanks.
    Mark

  • 0 in reply to Mark Huang44
    Prodigy 130 points

    Does anyone have some ideas?

  • 0 in reply to Mark Huang44
    TI__Mastermind 49110 points

    Hey Mark,

    Can you verify what the time scale on your scopeshot is? it looks like 100 milliseconds per division. I'm curious if the problem you are seeing is related to the power supply ramp rate if the divisions are in the milisecond range.

    Are you able to switch to the TCA9535 version of this device (some packages weren't migrated over).

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    TI__Guru 62910 points

    Hi Mark,

    Have you had a chance to look into Bobby's suggestions above?  If you are able to read and write from the device and don't detect issues with the default register configurations (which would indicate a faulty power-on-reset) then the simplest solution may just be to read the input port register at start-up in order to clear the interrupt.  This is a good best practice with the device, anyway, since an interrupt is generated whenever a port value changes.  If you don't first read the initial value, then, there wouldn't be any way to tell which port value changed when future interrupts are received.  Please let me know if that doesn't make sense.

    Regards,
    Max