Why does UART accept the signal without any failure in one conditions and doesn't accept the signal at all in the other conditions?

[ATmos.1]

Hello.

I have assembled the device on the STM32L496ZGT6P microcontroller. Along with the other functions, this controller is to poll its UART interface (more precisely, UART4). The device is operated outdoors and at low temperatures, and I have noticed that in the cold state this controller stops to receive the signal on its RX pin. I checked with an oscilloscope and with a UART-USB adapter and learnt that the signal goes to the RX UART4 pin. But the controller acts as if there is no signal on the RX UART4 at all. When the device is kept in room temperature for some time, it starts to function normally and does not fail in warm rooms. What can be the reason for such abnormality?

[PatrickF]

Hello,

Did you use the STM32MP1 together with STM32L4 (STM32MP1 series is the scope of this "STM32 MPUs' topic) ?

If not, I will move your question to "STM32 MCUs" topic.

Anyway, a a general answer, your issue at low temperature could be linked to clock used for UART. Internal oscillator drift (HSI or similar) migh go outside UART possible tolerances for accurate reception. In that case, you should get framing or similar error.

You could check the frequency of UART clock by probing UART_TX pin (bit duration is linked to UART clock).

May be solved by various ways (oscillator tuning Vs temperature, UART different settings, etc...) or better by using HSE (Crystal) which are far less sensible to temperature.

Regards,

Patrick

[ATmos.1]

Hi, Patrick!

I use STM32L496ZGT6P

Regards,

Andrew.