STM32F030 USART Transmit Issue

Hi All,

I am developing some code on the STM32F030R8 Nucleo dev board. I am having trouble getting my USART transmit to clock out. I am sending values to the comm port every 1s, and I am seeing nothing. I am also monitoring the pin on a scope and I see nothing.

After the code goes through the 'PrintRS232(Tx)' function I get a transmit complete flag and transmit empty flag in the ISR(TC and TXE), which is very confusing since I don't see any data transmitting.

I am using a watch window to monitor each bit getting transmitted and they are correct according to the ascii table.

I typically use Cortex M3 or M4 and never had an issue with USART. This is my first M0 project. I think I need some fresh eyes to go through this code.

#include <stm32f0xx.h>
#include "UART.h"          // USART Files

char UART_RX[50];
char *pRx;

void InitUART(void){
// Enable Clocks
        RCC->APB1ENR |= RCC_APB1ENR_USART2EN;        // Enable USART1 peripheral clk
        RCC->AHBENR  |= RCC_AHBENR_GPIOAEN;  // Enable Port A Clk for USART1

// Configure PA2 (Tx) and PA3 (Rx)
        GPIOA->AFR[0]  |=  0x01 << (2 * 4);      //AFRL, PA2, UART1
        GPIOA->AFR[0]  |=  0x01 << (3 * 4);      //AFRL, PA3, UART1
        GPIOA->MODER   &= ~0x000000F0;             //Clear PA2 & PA3
        GPIOA->MODER   |=  GPIO_MODER_MODER2_1;        //Alternate Fxn mode
        GPIOA->MODER   |=  GPIO_MODER_MODER3_1;        //Alternate Fxn mode
        GPIOA->OTYPER  &= ~GPIO_OTYPER_OT_2;       //Output Push/Pull
        GPIOA->OTYPER  &= ~GPIO_OTYPER_OT_3;       //Output Push/Pull
        GPIOA->OSPEEDR |=  GPIO_OSPEEDR_OSPEEDR2;  //PA2 high speed
        GPIOA->OSPEEDR |=  GPIO_OSPEEDR_OSPEEDR3;  //PA3 high speed
        GPIOA->PUPDR   |=  GPIO_PUPDR_PUPDR2_0;         //PA2 Pull up
        GPIOA->PUPDR   |=  GPIO_PUPDR_PUPDR3_0;         //PA3 Pull up

// Configure UART
        USART2->CR1 &= ~USART_CR1_UE;     //Disable UART for configuring
        USART2->CR1 &= ~USART_CR1_M;       //Data length = 8bits
        NVIC_EnableIRQ(USART1_IRQn);      //Enable USART1 IRQ
        USART2->CR1 |= USART_CR1_RXNEIE;  //Rx interrupt enable
        USART2->CR1 &= ~USART_CR1_PCE;     //No parity control
        USART2->CR1 &= ~USART_CR2_STOP;    //1 stop bit
        USART2->CR1 &= ~USART_CR3_CTSE;    //No hardware flow control
        USART2->CR1 &= ~USART_CR3_RTSE;    //No hardware flow control
        USART2->BRR = (SystemCoreClock/115200);      //Baud Rate of 115.2Kbps
        USART2->CR1 |= USART_CR1_RE;   //Recieve enable
        USART2->CR1 |= USART_CR1_TE;   //Transmit enable
        USART2->CR1 |= USART_CR1_UE;   //USART enable
        pRx = &UART_RX[0];            //pRx is pointed at first pos of buffer

//This function prints to the comm port via rs232
void PrintRS232(char* pString){
        USART1->CR1 |= USART_CR1_TE; // Set transmit enable bit
        while(*pString){                // Print char's as long as not a null char
                USART1->TDR = *pString;      // Put char into the data register
                while(!(USART1->ISR & USART_ISR_TXE));   // xfer to shift register
                pString++;                              // Increment ptr in memory
        }
}

Thanks,
- JMP