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TM4C1294KCPDT: GPIO PN0 is driven to high for some time and then to low before main function

Part Number: TM4C1294KCPDT
Other Parts Discussed in Thread: EK-TM4C1294XL

Dear Sir/Madam,

We found the pin is set to high for some time before any software code running and then set to low. We just use a while endless loop just after main and can verify this.

The pin in our design is to drive an external module and it should be low by default. We check the mannual and errata document and could not find any clue.

Can you please give us any clue for this? We just want the pin to be low after switching on

Thanks a lot,

Shoujie

  • Hello Shoujie,

    It sounds like there is some sort of software or configuration that is driving that behavior. Some questions to look into here:

    1) Is there any custom boot loader running on the device?

    2) Is there an RTOS involved with the application at all?

    3) If the pin is disconnected from all external modules, does it still drive a signal high? If not this would indicate the external device is responsible for that as the I/O are configured as Input on startup and would not be able to pull a signal low.

    4) Was there any code involving using the LED on the EK-TM4C1294XL ported over? I ask this simply because PN0 is connected to an LED on the evaluation kit so that came to mind.

    Best Regards,

    Ralph Jacobi

  • 1) Is there any custom boot loader running on the device?

    NO

    2) Is there an RTOS involved with the application at all?

    NO. We verify this by a endless loop after main function.  The signal goes from high to low itself after second or so!

    3) If the pin is disconnected from all external modules, does it still drive a signal high? 

    It is disconnected.

    4) Was there any code involving using the LED on the EK-TM4C1294XL ported over? I ask this simply because PN0 is connected to an LED on the evaluation kit so that came to mind.

    NO. We have our own board.

  • Hi,

      - Can you show your scope capture of PN0 relative to nRST and when when it becomes low? How long the pin was high?

      - Do you see the same behavior on other pins?

      - Can you see the same behavior on a EK-TM4C1294XL launchPad?

      - Can you show your code how you configure PN0?

  •   - Can you show your scope capture of PN0 relative to nRST and when when it becomes low? How long the pin was high?

    Probably later

      - Do you see the same behavior on other pins?

    No

      - Can you see the same behavior on a EK-TM4C1294XL launchPad?

    We do not test this.

      - Can you show your code how you configure PN0?

    We donot configure it: Just get the signal after main()

    int main()

    {

       while (true); // Use a scope to test PN0

    }

  • Hi,

      I'm working form home so don't have a scope with me to look at PN0. I can go to the lab next week. In the meantime it will help provide some clues if you can confirm PN0 on the LaunchPad.