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TMS320F28069: TMS320F28069PZT GPIO Pull Up

Don Kyle
Prodigy 30 points
Part Number: TMS320F28069

Tool/software:

When using several pins as a simple input and enabling the internal Pull Up, the input always reads as pulled up. I tried a stiff 2K pull down and the input still read high. I disable the pull up and I can read a low when pulled down externally and read a one when pulled up externally. What is the issue with the internal Pull up. I would think I could use it as a normal pull up. My current circuit does not have the external pull up, So I was hoping to use the internal pull up.

Thanks!

  • 0
    TI__Genius 16260 points

    Hi Don,

    I'm not sure I understand your question. From your description it sounds like the internal pull-up is working as expected. What behavior are you expecting / hoping to see instead?

    Thank you,

    Luke

  • 0 in reply to Luke Jones
    Prodigy 30 points

    My issue is what resistor must be used to pull the input with the pull up enable to produce an input of a zero? At the moment 

    Thanks for replying. 

    Don

  • 0 in reply to Don Kyle
    TI__Genius 16260 points

    Hi Don,

    The following table from the datasheet indicates the current consumption on a pin with pull up enabled and input voltage of 0V. From this information you can infer the resistance of the pull up resistor:

    3.3 / 0.000140 = 24k Ohms.

    The voltage on the pin is effectively the same as the voltage in the middle of a resistor ladder where the 3.3V resistor is 24k Ohm and the 0V resistor is your pull down resistor, the voltage will not be exactly 0 but can be very close to 0 with a strong pull down resistor like 100 Ohm for example.

    Thank you,

    Luke