STM32F401RET6 failed UART communication

[NealXu]

We just found few boards failed UART communication.

The debug process for this issue points to the LSI and RTC block inside the MCU STM32F401RET6.

The RTC block was driven by LSI (internal RC oscillator), these boards failed to initialize the RTC block and the program was stuck there during the source code debugging.

What could be the possible reason? Is it due to the floating pin of Tamper? Or something else?

Could you pls help check  whether ST had some update on the MCU parameters in 2022? Because we didn’t found this issue in MCU with date code of 2021. Thank you!

[waclawek.jan]

> these boards failed to initialize the RTC block and the program was stuck there during the source code debugging.

Where exactly was the program stuck?

Tell us about the power supply arrangement, including VDDA and VBAT.

Consider performing explicit backup domain reset, to avoid effects of backup domain brownout.

JW