Compute Module • Re: HDMI I2C busses usable when HDMI is unused?

You can, but you'll need to disable the HDMI port via device tree so that it doesn't get used for DDC purposes should the hot plug GPIO ever be asserted.

HDMI1_HOTPLUG (Pin 143) is not connected, so nothing bad should happen. Do you recommend an extra 1k pulldown for additional safety?
My idea is to use
dtoverlay=vc4-kms-v3d-pi5,nohdmi1
and write an own overlay that only sets status="okay"; in the ddc1 device tree node.

You also need to be aware that the controller does have limitations, which is why you'll see lots of addresses allegedly respond when using i2cdetect when there aren't devices on those addresses. i2cdetect -r works, so it's the SMBus "quick write" operation that is erroneous.

Thanks, I'll check this.

The CM5 datasheet says "5V tolerant" and "pulled up with 1.8k". What is the voltage on the other side of the pull-ups? Can I use 3.3V-only devices on these pins?

Statistics: Posted by fchk — Fri Apr 11, 2025 2:10 pm

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