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Unused pins- DM8127

Dimitriy Grigorovitch0
Prodigy 60 points

Hi,


I am  doing power optimization to a design based on DM8127. I have a lot of unused pins which are unconnected.

I have read section 5.4 in the datasheet, but still i have 4 open questions.

1. What is the direction that should be used for unused pins- input/output?

2. What is the preferred function- GPIO/ specific function?

3. What kind of pull should be used- Pullup or Pull-down?

4. in a case when same gpio can be muxed to 2 different balls (for example GP1[7] can be muxed to W1 or W6), what should i do with the second ball? (GP1[7] will be muxed to W1, what should I do with W6)?

I have read the datasheet, the section that talks about handling unused pins, but haven't found an answer to those specific questions.

Thanks,

Dimitriy.

  • 0
    TI__Guru**** 170625 points

    Dimitriy,

    Dimitriy Grigorovitch0 said:
    1. What is the direction that should be used for unused pins- input/output?

    I do not understand your question. Do you want to know the default/after_reset state of the unused pins?

    Dimitriy Grigorovitch0 said:
    2. What is the preferred function- GPIO/ specific function?

    When not used, you can leave the pin by it default/after_reset state. There is no preferred function for not used pins.

    Dimitriy Grigorovitch0 said:
    3. What kind of pull should be used- Pullup or Pull-down?

    To use pullup or pulldown external resistors depends on the default/after_reset state of this pin. For example if default state after reset is input and there is no internal pull resistor, then is preferred to add external pull up or pull down resistor (which is more easy to integrate in your design - pullup or pulldown). If there is internal pull resistor, then there is no need to add external pull resistor, you can use the internal.

    Dimitriy Grigorovitch0 said:
    4. in a case when same gpio can be muxed to 2 different balls (for example GP1[7] can be muxed to W1 or W6), what should i do with the second ball? (GP1[7] will be muxed to W1, what should I do with W6)?

    You can treat W6 as a normal unused pin.

    BR
    Pavel

  • 0 in reply to Pavel Botev
    Prodigy 60 points

    Hi Pavel,

    Thank you for your prompt reply.

    Pavel Botev said:

    Dimitriy Grigorovitch
    1. What is the direction that should be used for unused pins- input/output?

    I do not understand your question. Do you want to know the default/after_reset state of the unused pins?

    I know the default state, i want to configure all unused pins in the most energy saving way. The question is what is more power saving configuration- input or output (in case when direction can be changed like gpio).

    Pavel Botev said:
    Dimitriy Grigorovitch0
    2. What is the preferred function- GPIO/ specific function?

    When not used, you can leave the pin by it default/after_reset state. There is no preferred function for not used pins.

    So it is same power consumption if the pin is configured as GPIO or specific function?

    Pavel Botev said:
    Dimitriy Grigorovitch0
    3. What kind of pull should be used- Pullup or Pull-down?

    To use pullup or pulldown external resistors depends on the default/after_reset state of this pin. For example if default state after reset is input and there is no internal pull resistor, then is preferred to add external pull up or pull down resistor (which is more easy to integrate in your design - pullup or pulldown). If there is internal pull resistor, then there is no need to add external pull resistor, you can use the internal.

    The question is about internal pullup/pulldown. In my design the unused pins are not connected and may be floating. What is the preferred internal pull resistor-  up or down?

    Pavel Botev said:
    Dimitriy Grigorovitch0
    4. in a case when same gpio can be muxed to 2 different balls (for example GP1[7] can be muxed to W1 or W6), what should i do with the second ball? (GP1[7] will be muxed to W1, what should I do with W6)?

    You can treat W6 as a normal unused pin.

    What do you mean? this specific pin can be : DEVOSC_WAKE /  TIMER 5 / SPI[1]_SCS[1] /  GP1[7] .

    If it cant be GP1[7], what function should i assign to it?

    Thank you for your answers.

    Best Regards,

    Dimitriy.

  • 0 in reply to Dimitriy Grigorovitch0
    TI__Guru**** 170625 points

    Dimitriy Grigorovitch0 said:
    I know the default state, i want to configure all unused pins in the most energy saving way. The question is what is more power saving configuration- input or output (in case when direction can be changed like gpio).

    As datasheet does not state, I think there is no difference between input and output mode for unused pins, regarding power saving.

    Dimitriy Grigorovitch0 said:
    So it is same power consumption if the pin is configured as GPIO or specific function?

    Yes, it should be same power consumption when the pin is not used.

    Dimitriy Grigorovitch0 said:
    The question is about internal pullup/pulldown. In my design the unused pins are not connected and may be floating. What is the preferred internal pull resistor-  up or down?

    In the common case, we use the default internal pull resistor, thus there is no need to configure it. If there is no default pull resistor, there is no difference regarding power saving whether you will use internal pull up or down.

    Dimitriy Grigorovitch0 said:

    What do you mean? this specific pin can be : DEVOSC_WAKE /  TIMER 5 / SPI[1]_SCS[1] /  GP1[7] .

    If it cant be GP1[7], what function should i assign to it?

    I mean when not using W6 pin, you can leave it with its default muxmode state ([7:0] = 0), it is not necessary to select any mode on this pin, when you are planning to not use this pin.

    BR
    Pavel