BeagleBone AI Double Balls

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1

Hi!

I had a question regarding the I/O pins on BB-AI. I’ve noticed that on some of the pins on the expansion headers, there are two AM5728 balls connected to the same pin (through zero-ohm resistors). I’ve noticed these particularly on the pins used for the LCD.
I was wondering, what’s the convention going to be for these, i.e. if I wished to use them as GPIO instead of as for an LCD, then should I configure and use the first ball (and disable the second) or vice-versa?
At first thought it seems to me that it doesn’t matter either way, i.e. I should just pick one, but perhaps I’m missing something so I wanted to check. For instance if a future config-pin feature always uses the first ball, then I’d like to pick that one too, or if it will always use the second ball, then I’ll use that one.
Many thanks!

2

I’ve used the second ball (and disabled the first) when it was required for a device. For example spi2_d1 uses P9.21b, so I disable P9.21a by setting it to PULL_DIS | MUX_MODE15. Be careful about pull-up/pull-down contention between connected balls. Use the same pull mode for both or set the unused ball to PULL_DIS.

If you haven’t already use /opt/scripts/device/bone/show-pins.pl to get a nice summary of how things are configured. To use that script you first have to install a package: “sudo apt install libinline-files-perl”.