Programming UART on ARM Cortex-m4 TM4C123 Tiva C LaunchPad
In this example the TM4C123 micocontroller communicates with the PC by means of UART communication protocol. On the PC side, we need to download a serial terminal program to receive and send data from the pc. Tera Term is a highly recommended one, it can be downloaded just by doing a google search. After downloading and installing, follow the setup depicted in the two figures below.
When the program is opened, select the “Serial” radio-button and in the drop-down select “COMx :Stellaris Virtual Serial Port” or any other port name you think relates to your microcontroller (the names in the drop-down vary sometimes)
Tera Term Serial Port Selection
Tera Term Serial Port Settings
This is the default setting but just to sure go to Setup -> Serial Port…
and verify.
In the program presented below, when any key is pressed in Tera terminal, the LEDs on the TM4C123 Tiva C launchpad either change color or go off depending on the ascii value of the key pressed .
Note : The pressed key will not be printed in the terminal, just the LEDs will change.
Program :
#include "TM4C123.h" // Device header
#include <stdint.h>
char UART0Rx(void);
void delayMs(int n);
int main(void)
{
char c;
SYSCTL->RCGCUART |= 1; /* provide clock to UART0 */
SYSCTL->RCGCGPIO |= 1; /* enable clock to PORTA */
SYSCTL->RCGCGPIO |= 0x20; /* enable clock to PORTF */
/* UART0 initialization */
UART0->CTL = 0; /* disable UART0 */
UART0->IBRD = 104; /* 16MHz/16=1MHz, 1MHz/104=9600 baud rate */
UART0->FBRD = 11; /* fraction part, see Example 4-4 */
UART0->CC = 0; /* use system clock */
UART0->LCRH = 0x60; /* 8-bit, no parity, 1-stop bit, no FIFO */
UART0->CTL = 0x301; /* enable UART0, TXE, RXE */
/* UART0 TX0 and RX0 use PA0 and PA1. Set them up. */
GPIOA->DEN = 0x03; /* Make PA0 and PA1 as digital */
GPIOA->AFSEL = 0x03; /* Use PA0,PA1 alternate function */
GPIOA->PCTL = 0x11; /* configure PA0 and PA1 for UART */
GPIOF->DIR = 0x0E; /* configure Port F to control the LEDs */
GPIOF->DEN = 0x0E;
GPIOF->DATA = 0;
for(;;)
{
c = UART0Rx(); /* get a character from UART */
GPIOF->DATA = c << 1; /* shift left and write it to LEDs */ } } /* UART0 Receive */ /* This function waits until a character is received then returns it. */ char UART0Rx(void) { char c; while((UART0->FR & 0x10) != 0); /* wait until the buffer is not empty */
c = UART0->DR; /* read the received data */
return c; /* and return it */
}
/* Append delay functions and SystemInit() here */
void delayMs(int n){
int i,j;
for(i=0;i<n;i++){
for(j=0;j<3180;j++)
{}
}
}