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[AM3517] Preferred Pin Setting for Unused Pins

Chris Bobek
Prodigy 65 points
Other Parts Discussed in Thread: AM3517

The Reference Manual explains very nicely in section 6.5.3 how best to set unused pins for power optimization.  However, I have a couple questions:

1)  For an unused pin that can be Input, Output, or BiDir, which is best or preferred (input w/ pulldown or output driving 0)?

2)  Do I need to set the pin mode to mode 7 (safe_mode) on all my unused pins or do I set them as GPIOs?  Since safe_mode is a high-Z input, then I would just enable the pulldown, correct?  Or would I have to also write to the corresponding OE registers and set to input as well?.

Thank you very much.

  • 0
    TI__Guru 62975 points

    Which device are you using?

  • 0 in reply to tlee
    Prodigy 65 points

    Sorry, that would be helpful.  I am using the AM3517.

  • 0
    TI__Guru 64470 points

    Chris Bobek said:

    1)  For an unused pin that can be Input, Output, or BiDir, which is best or preferred (input w/ pulldown or output driving 0)?

    I would use the information in Section 6.5.3 of the technical reference manual as a guide to handle pins that you are not using.  It will depend on the default configuration of those pins after reset.  The flow chart in Figure 6-19 is a great way to determine how to configure the pins when not using them.

    For inputs that have an internal pullup/pulldown, enable the internal pulldown AND do not connect anything to the pin.  Leave it un-connected and unrouted.  The reason not to route the signal on your PCB is to limit the "opportunity" for noise to be picked up.

    For outputs or bi-directionals, configure the pin as an output and drive it low.

     

    Chris Bobek said:

    2)  Do I need to set the pin mode to mode 7 (safe_mode) on all my unused pins or do I set them as GPIOs?  Since safe_mode is a high-Z input, then I would just enable the pulldown, correct?  Or would I have to also write to the corresponding OE registers and set to input as well?.

    For those pins set to mode 7 (safe_mode), the output driver is disabled.  I would suggest enabling the pulldown, if available.