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Pin behavior during reset un-clear

Chris Smith
Intellectual 825 points

Hi, I'm trying to understand what state the various IO pins will take during a device reset.  I have some signals that must remain in certain states at all times so I'd like to understand better how the device behaves during reset.  I see in the reference manual that it may depend on the pull-up/pull-down control status.  In table 19-4 it says "Device- and module-specific"  What does that mean?  What I don't want to do is select a pin and then later find out that it always takes a certain state during reset and can't be changed via software.

Thanks,

Chris

  • 0
    TI__Genius 13810 points

    1. IO status during power-on-reset:

    IO buffer condition during power-on-reset (nPORRST is low): All I/O pins, except nRST, are configured as

    High-impedance while nPORRST is low and immediately after nPORRST goes high.

    IO pullup/pulldown condition during power-on-reset: all internal pullups and pulldowns on input pins are

    disabled when nPORRST is low, and become active immediately after nPORRST goes high. Pins that are

    listed with "programmable" have programmable pullups or pulldowns. The default value after reset is listed

    underneath "programmable" in the following table. The exceptions are nPORRST, nRST, nTRST and

    TEST pins. The pulls on these pins will be active during power-on-reset.

     

    2. IO status during nRST:

    Default pullups or pulldowns.

  • 0 in reply to Haixiao Weng
    Intellectual 825 points

    Haixiao, I don't see the table you mention.

    I'd like to connect the micro to a system signal that disables a potentially dangerous behavior.  Once the micro is up and running it will monitor a bunch of things and determine that nothing is dangerous and the system can be enabled.  When the micro is not running (for any reason) the system needs to default to a safe state.  So it seems that in this case it's best to do the following:

    1.  Make the disable signal active low.  System is disabled when signal is low.
    2.  Put external pull-down on disable signal.
    3.  Program default value after reset to low and pull-down resistor.
    4.  Seems the GIOA4_INT4 may be a good pin to use?

    Does that seem like a workable solution?

    Thanks,

    Chris

     

  • 0 in reply to Chris Smith
    TI__Genius 13810 points

    The table is table 2-8 in page 12 of the datasheet

    GIOA4 sounds a good selection.

    Regards,

    Haixiao