STM32WL30 change USART baud rate

PhilippR · ‎2025-09-16

Hello everyone,

I'm working with the STM32WL30 and I'm trying to change the baud rate of the USART peripheral. However, I'm encountering some issues when I change the baud rate.

The function I wrote for changing the baud rate looks like this:

void changeBaudRate(uint16_t baudRate) {
  // start USART reset
  RCC->APB1RSTR |= RCC_APB1RSTR_USARTRST;
  // disable interrupt
  NVIC_DisableIRQ(USART1_IRQn);
  // stop reset
  RCC->APB1RSTR &= ~RCC_APB1RSTR_USARTRST;

  // set BRR
  USART1->BRR = 16000000 / baudRate;
  // set CR1
  USART1->CR1 = USART_CR1_RXNEIE_RXFNEIE | USART_CR1_TE | USART_CR1_RE | USART_CR1_UE;

  // set IR prio
  NVIC_SetPriority(USART1_IRQn, 1);
  // enable IR
  NVIC_EnableIRQ(USART1_IRQn);
}

When I changed the baud rate for the first time, everything works fine and I receive the messages. If I change the baudrate to another value, I won't receive messages on the new baud rate, but still with the previously configured baud rate. When I debug the baud rate change, I can see, that the BRR was changed to the new value, but somehow the peripheral still uses the previous BRR value.

I also used this logic with a STM32G0 controller without any problems.

Thank you in advance for your help!

Best regards,
Philipp