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SUPER URGENT: PCA9539 Logic Read Problem

Jefferson Chai
Prodigy 30 points
Other Parts Discussed in Thread: PCA9539, TCA9539

We are using the OMAP1621 with the PCA9539. Whenever we initiated a power-on-reset to the PCA9539 and perform an initialization of the IOs, the IOs does not get configured correctly. We are trying to initialize 2 pins as the input pin and read the information from it after a power-on-reset but because of this problem, we will be reading a false input information. I read from the datasheet saying the time to reset is 400ns. I assume this is the time needed for Vcc to stay below 0.2V for a power-on-reset before coming up back to operating voltage. Our Vcc stays low for 100ms before coming back up to operating voltage. Is there additional initialization codes we can do to get this logic gates up and running moment we initialize the IOs.

Thanks!

  • 0
    TI__Genius 9085 points

    We are working with you directly with this issue, but I will post the following for other forum users :

     

    The reset time in the datasheet refers to the reset pin. For the PCA9539, the Vcc has to stay low longer than 100ms under certain conditions.

    It's recommended you switch to the TCA9539. The POR on the TCA device has less demanding Voff and Toff requirements. These are spec'ed in the TCA datasheet.

    If  switching devices is not an option, you can also use the external reset pin to reset the device. Additionally, writing to all of the registers after an incomplete POR will ensure correct operation.