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PCA9538: INT pin setting

Alan Chang
Intellectual 1960 points
Part Number: PCA9538

Hi all,

   A question about PCA9538 INT behavior below,


1. Our GPIO P0-7 are all LOW  in standby mode. (by external HW logic)
    so the default input value is "0000 0000"
2.  when power on , P0-7 is 1111 1100. (P0-P5 is Pull high by external logic)
3.  If  we want to trigger INT pin in main power on, when p0-p5 is going to 1 from 0.
       do we need to invert default setting of p0-p5 in standby mode?  so the default input becomes "1111 1100"

Thanks

  • 0
    TI__Mastermind 47895 points

    Hi Alan,

    The interrupt pin will asset when the current state of an IO input pin differs from what is stored in the device memory in the Input Port Register. The initial state of this register is determined when the device is powered on. This register is also updated after a read. If the input values are LOW during power-up (or previous read) and then change to HIGH after the device is active, an interrupt will be asserted. The Polarity configuration of the pin will not impact this behavior.

    Let me know if this answers your question.

    Regards,
    Eric

  • 0 in reply to Eric Schott1
    TI__Intellectual 1960 points

    Hi Eric,

      Thanks for your answer. So when system changes to ON mode from standby mode, the P0~P5 states are changed to "H" from "L" by external pull-up, but I2C register don't modify (still on previous setting). On this condition, INT pin should be asserted, right?

      

  • 0 in reply to Alan Chang
    TI__Mastermind 47895 points

    Hi Alan,

    Yes, your understanding is correct. This is assuming that enough time has passed for PCA9538 to power-on completely before the pin states change.

    Regards,
    Eric