GPIO pull-down resistors

From looking at the Xavier carrier board design file schematic and the carrier board specification document, GPIO pins such as board pins 22 and 15 should have 1Mohm pull-down resistors. Yet when using the Jetson.GPIO library they seem to behave as if they don’t have such resistors, and when I measure the resistance between one of those pins and ground I see no connection at all.

What am I missing here? How do I use GPIOs with internal pull-down resistors?

hello WasabiFan,

please download Pinmux spreadsheets via Jetson Download Center,
and you might refer to Jetson AGX Xavier MB1 Platform Configuration chapter for configure GPIOs.
thanks

Can you expand on that? I don’t understand what you are suggesting I do to fix the problem.

I’ve already looked at the pinmux spreadsheet, but it also says that the pin has a pull-down resistor (I assume the configuration shown in the spreadsheet is the default one for the Xavier). Are you saying I should be changing the configuration?

hello WasabiFan,

please modify the pinmux spreadsheet, customize the content below “Filled in by Customers” column.
once you finish the modification, you’ll need to click the [Generate DT file] to output new gpio and pinmux device tree files, please also check [Jetson AGX Xavier MB1 Platform Configuration chapter] for the steps to create the cfg file.
you’ll need to re-flash the board with the new cfg files to make the change.
thanks

I don’t want to change the device tree configuration: I want to understand the default configuration. Why do the data sheets appear to incorrectly report the default pin configuration, and where can I find correct information?

hello WasabiFan,

you could check the default configuration as below cfg file,
for example,

$OUT/Linux_for_Tegra/bootloader/tegra19x-mb1-pinmux-p2888-0000-a04-p2822-0000-b01.cfg

you might also check Jetson AGX Xavier Developer Kit Carrier Board Design Files, for carrier board design files.
thanks

I understand that you’re trying to answer my question but you aren’t giving the relevant information. Specifically, what document and page should I look at to identify whether a particular pin has a pull-up or pull-down resistor? Please show me the document and page. I don’t want to be crawling through config files.

Checking the live configuration on a particular Jetson might happen to work, but the behavior should be documented without having to boot up and connect to the device. The design files are a ZIP folder of dozens of documents, and I haven’t been able to find one which aligns with the apparent behavior of the board.

1 Like

hello WasabiFan,

had you open pinmux spreadsheet for checking?
you’ll found PD/PU configuration in the pinmux spreadsheet.
thanks

Yes. GPIO17 (pin 22 on the main GPIO header) is listed as having a 100k pull-down resistor in the spreadsheet, but it doesn’t behave like it has a pull-down resistor in practice when I tested it.

1 Like

What code did you use to test it? What hardware did you use to test it?

The combination of MPIO / Pinmux / GPIO mux / Rail configurations / Voltage translation on carrier boards is somewhat bewildering …