To activate a UART you will need to turn on the UART clock in the RCGC1 register. You should also turn on the clock for the digital port in the RCGC2 register. You need to enable the transmit and receive pins as digital signals. The alternative function for these pins must also be selected. In particular we set bits in both the AFSEL and PCTL registers.

• baud_rate = Baud16/16 = (bus_clock)/(16*divider)
• divider = (bus_clock / baud_rate) / 16

divider : Partie entière dans IBRD, partie flottante * 64 dans FBRD.

void UART_Init(void){            // should be called only once
  SYSCTL_RCGC1_R |= 0x00000002;  // activate UART1
  SYSCTL_RCGC2_R |= 0x00000004;  // activate port C
  UART1_CTL_R &= ~0x00000001;    // disable UART
  UART1_IBRD_R = 43;     // IBRD = int(80,000,000/(16*115,200)) = int(43.40278)
  UART1_FBRD_R = 26;     // FBRD = round(0.40278 * 64) = 26
  UART1_LCRH_R = 0x00000070;  // 8 bit, no parity bits, one stop, FIFOs
  UART1_CTL_R |= 0x00000001;     // enable UART
  GPIO_PORTC_AFSEL_R |= 0x30;    // enable alt funct on PC5-4
  GPIO_PORTC_DEN_R |= 0x30;      // configure PC5-4 as UART1
  GPIO_PORTC_PCTL_R = (GPIO_PORTC_PCTL_R&0xFF00FFFF)+0x00220000;
  GPIO_PORTC_AMSEL_R &= ~0x30;   // disable analog on PC5-4
}
// Wait for new input, then return ASCII code
unsigned char UART_InChar(void){
  while((UART1_FR_R&0x0010) != 0);      // wait until RXFE is 0
  return((unsigned char)(UART1_DR_R&0xFF));
}
// Wait for buffer to be not full, then output
void UART_OutChar(unsigned char data){
  while((UART1_FR_R&0x0020) != 0);      // wait until TXFF is 0
  UART1_DR_R = data;
}
// Immediately return input or 0 if no input
unsigned char UART_InCharNonBlocking(void){
  if((UART1_FR_R&UART_FR_RXFE) == 0){
    return((unsigned char)(UART1_DR_R&0xFF));
  } else{
    return 0;
  }
}