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TMS320F28027F: how to set low all GPIOs from very beginning of power up.

Dave Hunson
Expert 1760 points

Part Number: TMS320F28027F

hi everyone

Good day!

before boot the MCU I want all of GPIOs pin to be low, before get mode,

Since it is take a long time to configure it in program (~20ms).

do you have any solution? 

how to set low all GPIOs from very beginning of power up.

thanks 

Dave.

  • +1
    TI__Mastermind 42195 points

    Dave,

    on this device pull-down resistors must be placed on critical signals which cannot glitch during the power up sequence. Typically this is done for any signal that connects to some sort of power electronics.

    After power up the internal pullups can be disabled and the GPIO mux configured to its desired state.

    Regards,
    Cody  

  • 0 in reply to Cody Watkins
    Expert 1760 points

    thanks dear Cody  

    I am using GPIO07 for inrush Relay and it is so critical .I had Unwanted start inrush Relay at very beginning of power up!!!

    it damaged my module,

    would you please tell me ohm of pull down resistor for GPIO?

    thanks for your attention.

    Dave.

  • 0 in reply to Cody Watkins
    Expert 1760 points

    Dear Cody,

    I found your answer to someone who had the same problem around 2years a go .

    "

    To keep the GPIO in a known state you should add a pull-down resistor externally to the device. Ideally you will choose a GPIO without the pull up enabled by default, but the internal pull up is weak and can be overpowered by an external resistor. 10K ohms works for many applications for noisy applications 2.2K is recommended, but you will need to evaluate your system and determine the best value.

    "

    as you mentioned here the internal  internal pull up is weak and can be overpowered by an external resistor. 10K ohms!! if so,then why it can trun on the Optcoupler !!??? as far as I know Optocupler needs more than 10mA to turn it's LED on ..

    thanks for attention.

    Dave.

  • +1 in reply to Dave Hunson
    TI__Mastermind 42195 points

    Dave,

    do you have a buffer between the GPIO and the optocoupler? Even the GPIO's output buffer shouldn't be able to drive 10mA safely. The limit is 4mA per IO.

    If you do have a buffer then I would suspect that the weak internal pull up may be strong enough to pull the buffer high.

    Regards,
    Cody

  • 0 in reply to Cody Watkins
    Expert 1760 points

    Cody ,

    Sure I do have buffer , and you are right in this case  by 2.2k ohm will solve my problem