STM320U LPUART2 not working after waking up from the STOP0/ Sleep Mode.

[suresh kumar1]

Hello Everyone,

I am currently using LPUART2 for communication between an MCU (STM32U031) and an MPU (Application Processor).
Configuration parameters:

• Baud rate: 9600
• Stop bits: 1
• Parity: None
• Data bits: 8

Description:

Data exchange between MCU and MPU works perfectly when both devices are operating in normal power mode (i.e., not in sleep or stop modes). However, I am facing an issue when both MCU and MPU wake up from sleep/stop mode.

After wake-up ,The MCU is unable to receive data from the MPU, even though the MPU continues transmitting data. No IRQ handler is triggered on the MCU side.

Additional Details:

1. I deinitialize the LPUART before entering sleep/stop mode.
2. I reinitialize it immediately after wake-up.

Scenarios Tested:

Only MPU enters sleep (MCU remains active): After MPU wake-up, communication works perfectly.

Both MPU and MCU enter sleep: After wake-up, communication fails (MCU doesn’t receive data).

Observation:

It seems that the issue is related to LPUART behavior during low power transitions, since everything works fine when only the MPU performs sleep/wake operations and the MCU remains awake.

Please help identify if there is missing configuration or specific setup required for LPUART in low power modes?

I am open to share the source code and any other information.

[Gyessine · Accepted solution]

hello @suresh kumar1 

Do you get the same issue when you try using LPUART1?

You can refer to the provided examples for guidance : example 1,example 2

BR
Gyessine