I2C pull-up breaks unrelated USB communication.

RE: I2C pull-up breaks unrelated USB communication.

Snowleo — Mon, 13 Feb 2023 14:08:24 GMT

My best guess is, that the code behaved differently, when I2C was working (due to the pull-up being active), which resulted in the output buffer being empty on the USB/UART by the time I connected to it.

RE: I2C pull-up breaks unrelated USB communication.

Simonr — Mon, 13 Feb 2023 13:41:28 GMT

Glad to hear you found the answer. We're just interested in knowing why the USB/UART and I2C would be correlated at all? Do they use the same TX/RX pins, or have conflicting priorities somewhere in your project?

Best regards,
Simon

RE: I2C pull-up breaks unrelated USB communication.

Snowleo — Sat, 11 Feb 2023 21:03:13 GMT

I've found the answer myself. I didn't wait for DTR signal on the cdc_acm_uart device in my code, so the buffer was already empty by the time I connected to it on my PC.

RE: I2C pull-up breaks unrelated USB communication.

Snowleo — Sat, 11 Feb 2023 19:14:34 GMT

I've updated the configuration in the original post with a better one. I've by now also tried to use an external 10k pull-up on the I2C lines, the same behaviour exists with that as well. I think the issue might be, that I am using the pins (20 and 24) that were originally assigned to UART0 RX and TX for I2C.