NUCLEO-STM32L432KC: How to use UART through USB?

Question

Back with my STM32 adventures(data sheet). This time trying to get UART data through the USB. Essentially I want to be able to print over usb to start printing out variables to further debug code.

I am using the classic NUCLEO-L432KC board and I read somewhere for debug purposes you can print through the USB (ST-LINK) by setting up UART on the PA_2 pin.

What I have tried doing is setting up PA_2 to be a UART_2_TX pin and transmitting a constant decimal number (0x50) then using my mac terminal to 'screen" into the com port of the NUCLEO board. However I am getting this? The UART is working as on the oscilloscope scope I am getting data through. Any idea whats going on?

In terminal using: screen /dev/tty.usbmodem1423 9600

The code:

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; Copyright (c) 2020 STMicroelectronics.
  * All rights reserved.</center></h2>
  *
  * This software component is licensed by ST under BSD 3-Clause license,
  * the "License"; You may not use this file except in compliance with the
  * License. You may obtain a copy of the License at:
  *                        opensource.org/licenses/BSD-3-Clause
  *
  ******************************************************************************
  */
/* USER CODE END Header */

/* Includes ------------------------------------------------------------------*/
#include "main.h"


int main(void)
{
    RCC->APB1ENR1 |= (1<<17); // Enable USART2 Clock
    RCC->AHB2ENR = (1<<0); //Enable GPIOA Clock
    RCC->CCIPR = (1<<2); //Use the System Clock for USART2

    GPIOA->MODER &= ~(1<<4); //Enable Alt Function for PA_2
    GPIOA->AFR[0] = ((1<<10) | (1<<9) | (1<<8)); //Enable USART2_Tx for PA_2

    USART2->CR1 = (1<<3); //Enable Transmitter
    USART2->BRR = 0x1A0; //9600 baudrate
    USART2->CR1 |= (1<<0); //Enable USART2

  while (1)
  {
      USART2->TDR = 0x50; //Put data in the Transmitter reg
      while(((USART2->ISR) & (1<<7)) == 0); //Wait till transmitter reg is empty
  }


}

Answer 1

There was a screen process still running in the background that didn't close properly. Force closing the remaining process and restarting screen worked.