UART

UART Driver Initialisation

1. Activate clock gate controls for your desired UART and GPIO ports:

   • UART is under RCGC1
   • GPIO under RCGC2

2. Configure the UART registers:

   • Disable the UART module using UARTEN under UARTCTL

   • Calculate/Set the Baud Rate's Integer and Fractional value:

     • UARTIBRD = (Clock speed / (16 * Desired Baud rate))

       • `ie: (50,000,000 / (16 * 115,200)) = (27.1267) = 27`

     • UARTFBRD = (UARTIBRD's -nth remainder * 64 + 0.5)

       • `ie: (0.1267 * 64 + 0.5) = 8 `

   • Set the number of bits to be transmited using WLEN under UARTLCRH
   • Enable FIFO using FEN under UARTLCRH
   • Re-enable the UART module using UARTEN under UARTCTL

3. Configure the GPIO registers:

   • Enable Alternative Function for UART's TX and RX under GPIOAFSEL
   • Enable Digital Pins for UART's TX and RX under GPIODEN

   • Configure which bits in GPIOPCTL should be the alternative function

     • `ie: GPIO_PORTA_PCTL_R = (GPIO_PORTA_PCTL_R&0xFFFFFF00)+0x00000011; `

   • Disable analog functionality on TX and RX bits under GPIOAMSEL

Example: UART Driver Initialisation

void UART_Init(void){
  // Step 1:
  SYSCTL_RCGC1_R |= 0x00000001; // activate UART0
  SYSCTL_RCGC2_R |= 0x00000001; // activate port A
  
  // Step 2:
  UART0_CTL_R &= ~0x00000001; // disable UART
  UART0_IBRD_R = 27;  // IBRD = int(50,000,000 / (16 * 115,200)) = int(27.1267)
  UART0_FBRD_R = 8;   // FBRD = int(0.1267 * 64 + 0.5) = 8                     
  UART0_LCRH_R = (0x00000060|0x00000010); // 8 bit word length 
  UART0_CTL_R |= 0x00000001; // enable UART
  
  // Step 3:
  GPIO_PORTA_AFSEL_R |= 0x03;  // enable alt funct on PA1-0
  GPIO_PORTA_DEN_R |= 0x03;  // enable digital I/O on PA1-0                                  
  GPIO_PORTA_PCTL_R = (GPIO_PORTA_PCTL_R&0xFFFFFF00)+0x00000011;  // configure PA1-0 as UART
  GPIO_PORTA_AMSEL_R &= ~0x03;  // disable analog functionality on PA
}