Universal Asynchronous Receiver-Transmitter (UART)

Complete Lab Manual

For the complete experiment including learning objectives, theoretical background, and detailed explanations, download the PDF manual: Download Experiment 9 PDF

Examples

main.c

#include <stdio.h>
#include "TM4C123.h"
#include "uart.h"

int main(void) {
    UART0_Init();
    UART0_WriteString("Hello World!\r\n");  // Send greeting with newline

    while (1) {
		char buff[16];
		UART0_ReadString(buff, 16);
		
		UART0_WriteString("Received: ");
		UART0_WriteString(buff);
		UART0_WriteString("\r\n");
    }
}

uart.c

#include "uart.h"
#define MAX_STR_LEN 50
// Function to send a single character via UART0
void UART0_WriteChar(char c) {
    // Wait until the transmit FIFO is not full
    // UART0->FR bit 5 (TXFF) = 1 means FIFO is full, so wait until it becomes 0
    while ((UART0->FR & (1 << 5)) != 0);
    // Write the character to the Data Register to transmit
    UART0->DR = c;
}

// Function to send a null-terminated string via UART0
void UART0_WriteString(char *str) {
    // Loop through each character until null terminator
    while (*str) {
        // Send each character using UART0_WriteChar
        UART0_WriteChar(*(str++));
    }
}

// UART0 initialization function
void UART0_Init() {
    // Enable clock to UART0 module (bit 0)
    SYSCTL->RCGCUART |= (1 << 0);
    // Enable clock to GPIO Port A (bit 0)
    SYSCTL->RCGCGPIO |= (1 << 0);

    // Enable alternate function on PA0 (RX) and PA1 (TX)
    GPIOA->AFSEL |= U0_RX | U0_TX;
    // Configure PA0 and PA1 pins for UART function in Port Control Register
    // U0_RX corresponds to PA0 (bits 3:0) and U0_TX corresponds to PA1 (bits 7:4)
    GPIOA->PCTL |= (1 << 0) | (1 << 4);
    // Enable digital function for PA0 and PA1 pins
    GPIOA->DEN |= U0_RX | U0_TX;

    // Disable UART0 while configuring
    UART0->CTL = 0;
    // Set integer baud rate divisor for 115200 baud with 50MHz clock
    UART0->IBRD = 27;
    // Set fractional baud rate divisor
    UART0->FBRD = 8;
    // Configure Line Control for 8 data bits, no parity, one stop bit, and FIFOs enabled
    // 0x60 = 0b01100000: bit 6 (FEN) = 1 enable FIFO, bits 5-6 (WLEN) = 11 for 8 bits
    UART0->LCRH = 0x60;
    // Use system clock for UART
    UART0->CC = 0;
    // Enable UART0, TX and RX
    // Bit 0 = UARTEN, bit 8 = TXE, bit 9 = RXE
    UART0->CTL = (1 << 0) | (1 << 8) | (1 << 9);
}

char UART0_ReadChar(void) {
    while (UART0->FR & (1 << 4));  // Wait while RX FIFO empty
    return (char)(UART0->DR & 0xFF);
}

void UART0_ReadString(char *buffer, int maxLen) {
    int i = 0;
    char c;

    while (i < (maxLen - 1)) {   // Leave space for null terminator
        c = UART0_ReadChar();

        // Echo character back (optional)
        UART0_WriteChar(c);

        if (c == '\r' || c == '\n') {  // End of input
			UART0_WriteString("\r\n");
            break;
        }

        buffer[i++] = c;
    }

    buffer[i] = '\0';  // Null terminate the string
}

uart.h

#ifndef UART_H
#define UART_H

#include "TM4C123.h"  // Or your MCU's main header

#define U0_TX 2
#define U0_RX 1

void UART0_WriteChar(char c);
void UART0_WriteString(char *str);

char UART0_ReadChar();
void UART0_ReadString(char *buffer, int maxLen);

void UART0_Init();




#endif // UART_H

The above code demonstrates a simple UART communication setup. The UART0_Init function initializes the UART0 module, while UART0_WriteChar and UART0_ReadChar functions handle data transmission and reception, respectively. To be able to communicate with the microcontroller, you can use a terminal program on your PC PuTTY to send and receive data over the serial port. Make sure to set the baud rate and other parameters to match the configuration in your code. The following image shows how to set up the serial connection in PuTTY:

You should replace the COM port with the one assigned to your TM4C123G LaunchPad. You can find this in the Device Manager under Ports (COM & LPT). The baud rate should match the one set in your code (e.g., 115200).