GPIO issue of 33Mhz noise

Hi all,

I am trying to experiment with multiple gpio pins on my jetson agx xavier.

The output voltage of a particular gpio pin does not change from a 33MHz sine wave.

  • Experimental setup

    1. To see the output of the Jetson AGX Xavier Expansion Header, I connected the GND of pin number 39 to the GND of the oscilloscope.

    2. After starting Xavier, I ran /samples/ from the GitHub - NVIDIA/jetson-gpio: A Python library that enables the use of Jetson's GPIOs repository.

    3. I looked at the output of each gpio pin on the oscilloscope.

  • Result

    1. As a result, a sine wave of about 33Mhz was observed on the gpio pins with pin numbers 7,12,13,15,18,19,21,22,23,24,26,35,38,40 as shown below.

      When I pressed ctrl+C to move to the next pin output, the sine wave continued to appear on the screen, and when I disconnected the oscilloscope probe and reconnected it, the sine wave disappeared.

    2. On the other hand, on pins 11, 16, 29, 31, 32, and 33, the voltage was as expected, taking a value of 0 or 3V every 250ms, as shown below.

How can I get all gpio pins to output the expected voltage instead of a sine wave?

The results of displaying the version are as follows.

$ cat /etc/nv_tegra_release
# R32 (release) , REVISION: 6.1, GCID: 27863751, BOARD: t186ref, EABI: aarch64, DATE: Mon Jul 26 19:36:31 UTC 2021

Thanks for the help.

This could be way off, but is it still a sine wave if you have a 10k ohm resistive load?

Did you read the doc of 40 pin header as below? There are level shift on the pins, so there are some requests to the load.

Jetson Nano Developer Kit 40-Pin Expansion Header GPIO Usage Considerations Applications Note in DLC.

Thanks for the reply.

From notes Trumany provided, I see that the output of the level-shifted pin is sine wave of 33MHz and the output on pins that are not level-shifted are as expected.

However, I still do not know how to wire it to get the expected voltage from level-shifted pins.

The current wiring of the oscilloscope and Xavier is as follows.

If a register is needed, how should it be wired?

I am just suggesting adding 10k ohm as a test. For now you could just use wire wrap or 0.1" pin crimp connectors on a 10k resistor. I suspect (but don’t know for sure) that if the level shift is under a slight load it might again be square wave.

Hi, have you read the 40-pin doc? Did you probe the signal directly by removing 10k load?

Thank you all.
As Trumany said, I removed the 10kΩ resistor and attached the oscilloscope ground to Pin 39 and the oscilloscope probe directly to the pin whose voltage I wanted to know. Then I was able to measure the voltage as expected on all pins.

My knowledge of the oscilloscope was incorrect and I had installed a 10kΩ resistor.

I don’t understand exactly why the 10kΩ resistor didn’t give me the correct waveform, but I am happy to have solved the problem.

Thank you all for your help.

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