Configuring BeagleBone Black GPIO to Open Drain Output

[mraulsol]

Hi,

Is there a way for BBB GPIOs to be configured as Open Drain output? How?

If yes, which GPIOs have the open drain mode aside from the I2C pins? 

Thanks,

[Bill Gatliff]

You can't directly. What you do instead is switch them between input and output modes, and use pull-up (or pull-down, I always forget which) resistors as needed. The in-built ones may be sufficient if you enable them, depends on what your external hardware looks like.

Not a flaw of Linux or the chip, it's just how the hardware works to accommodate push-pull as well.  Many embedded chips work this way.

Other parts can do true open-drain, but nothing in the Beagle family that I recall. The above is usually close enough, especially since the GPIO driver and hardware can switch between input and output modes in a single instruction cycle, i.e. atomically, and the driven state is preserved as well.

b.g.

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[mraulsol]

Thanks for this! I'm still learning about BeagleBone and I got used to this mode being readily available for most microcontroller GPIOs.

So, does this mean, I have to do the following:

Logic 0 - Output mode driven to low

Logic 1 - Input mode with pullups (external)

???

[jonnymo]

It might be best to post in the BeagleBoard Forum since the Google thing is/was being deprecated.

https://forum.beagleboard.org/c/general/8

However, here be a few references you might find useful.

https://github.com/beagleboard/beaglebone-black/wiki/System-Reference-Manual

https://beagleboard.org/black

https://docs.google.com/spreadsheets/d/1fE-AsDZvJ-bBwzNBj1_sPDrutvEvsmARqFwvbw_HkrE/edit?usp=sharing&urp=gmail_link

Cheers,

Jon

To view this discussion on the web visit https://groups.google.com/d/msgid/beaglebone/c74f9cc3-ebe5-4674-9b7b-6b11d78b2e15n%40googlegroups.com.

[Bill Gatliff]

On Tue, Aug 31, 2021, 10:55 PM 'mraulsol' via BeagleBone <beagl...@googlegroups.com> wrote:

So, does this mean, I have to do the following:

Logic 0 - Output mode driven to low

Logic 1 - Input mode with pullups (external)

???

Yes.