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Original question:

Question about Pulldown of GPIO in F28335

TMDSCNCD28335: Question about Pulldown of GPIO in F28335

Joel Filipe Guerreiro
Prodigy 20 points
Part Number: TMDSCNCD28335
Other Parts Discussed in Thread: TMS320F28335,

Hello fellows,

I am developing a UPS hardware using F28335 microcontroller. For driving some relays, I am using GPIOs 30, 31, 84, 85, 86 and for initialization, I need to keep the voltage on these pins low to avoiding accidents.

However, even if I use a pulldown resistor of 1k Ohms on each gpio, (which is the minimum recommended in section 3.4.1 of www.ti.com/.../spraas1c.pdf) some pins remain high (GPIOs 84, 85, 86), with a voltage of about 1.5V, while the others (GPIOs 30, 31) go low with 0.12V.

How to pulldown GPIOs on TMDSCNCD28335 / TMS320F28335? Will it damage the GPIO if I use resistance lower than 1k Ohms?

Thanks for any support.

  • 0
    TI__Mastermind 41415 points

    Joel,

            a 1K Pull-down resistor should be strong enough to pull the pin to a low value.

    1. Do you have another potential driver on the node?
    2. Have you checked for shorts?
    3. Is it possible that you code is driving the GPIO to a 'high'?
      1. During boot up the device samples GPIOs 84,85, 86, and 87. These pins are configured as an input during this time and therefore shouldn't be causing this issue.
    4. How long after device power up are you seeing these pins go high?

    Regards,
    Cody 

  • 0 in reply to Cody Watkins
    Prodigy 20 points

    Hi Cody,

    Thanks for the reply.

    In the end, these pins are set high using the control SW2 switches. I turn them off and the problem disappeared.

    Regards,