R3, 499 ohm. Awesome, that's it! Thank you. I'll move the input to a different pin in a future hardware revision which also allows me to keep the UART0 debug interface for debug.

Thanks,
Eric

I am using GPIO43 UART0 TX in open-drain configuration with a 1K pull-up resistor to 3.3V. When in this mode, the voltage is only pulled down to 1.16V instead of 0V. If I use GPIO44, the voltage is pulled down to 0V. I could not find anything in the datasheet, TRM, or other documentation that mentio...