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STM32L4: UART problems with RX pin forked

Question asked by cillerai.dario on Jan 15, 2018



Rx signal from an external card is forked (by HW) to the pins of STM32L486RGT6:


- UART5 RX (PD2);

- PC13 (Wakeup#2).


Then, a reception from UART 5 will wake up the microcontroller from Standby mode (this is OK).


However, wrong characters are sometimes  received in UART5 RX (problems in UART1 have been also observed).

If the fork is disabled (RX signal delivered only to PD2) the problem is not present.


Note that:


- problem is present even if PC13 is configure in INPUT/ANALOG;

- input signal to PD2 observed by a scope is correct;

- PC13 RTC features are disabled.


It seems that the forked signal is causing trouble to the UART reception inside the Microcontroller!


Has anyone observed anything similar?