I was using I2C for the first time, as part of a brushess ESC project, and had to learn the hard way that internal (to the mcu) pull-up resistors would not work

I was using I2C for the first time, as part of a brushess ESC project, and had to learn the hard way that internal (to the mcu) pull-up resistors would not work at any reasonable (for my needs) communication speed. This post compares the performance of the circuit using the internal pull-up resistors against external 1kohm resistors, including plots showing the improved signal quality.