TM4C123 Timer1 using prescaler

Use prescaler register for TimerA to create 1-second delay

• Using prescaler of 250 gives us 16MHz/250 = 64000Hz. That means the clock fed to timer A is 1/64000Hz = 15.625 msec.
• To get one second delay, we need 1sec/15.625ms = 64000 for the match register.

1. /*

2.  * Timer using prescaler

3.  * This program incorporates the use of prescaler to create a longer delay.

4.  * Also the use of timer has been changed to TimerA of timer Block 1.

5.  *

6.  */

8. #include <stdint.h>

9. #include "inc/tm4c123gh6pm.h"

11. void timer1A_delaySec(int ttime);

13. int main (void)

14. {

15.     SYSCTL_RCGC2_R |= 0x00000020;   /* enable clock to GPIOF at clock gating control register */

17.     GPIO_PORTF_DIR_R = 0x0E;        /* enable the GPIO pins for the LED (PF3, 2, and 1) as output */

18.     GPIO_PORTF_DEN_R = 0x0E;        /* enable the GPIO pins for digital function */

20.     while(1) {

21.         GPIO_PORTF_DATA_R = 4;      /* turn on blue LED */

22.         timer1A_delaySec(1);        /* TimerA 500 msec delay */

23.         GPIO_PORTF_DATA_R = 0;      /* turn off blue LED */

24.         timer1A_delaySec(1);        /* TimerA 500 msec delay */

25.     }

26. }

28. /* multiple of second delays using periodic mode and prescaler*/

29. void timer1A_delaySec(int ttime)

30. {

31.     int i;

33.     SYSCTL_RCGCTIMER_R |= 2;        /* enable clock to Timer Block 1 */

35.     TIMER1_CTL_R = 0;               /* disable Timer before initialization */

36.     TIMER1_CFG_R = 0x04;            /* 16-bit option */

37.     TIMER1_TAMR_R = 0x02;           /* periodic mode and down-counter */

38.     TIMER1_TAILR_R = 64000 - 1;     /* TimerA interval load value reg */

39.     TIMER1_TAPR_R = 250 - 1;        /* TimerA Prescaler 16MHz/250=64000Hz */

40.     TIMER1_ICR_R = 0x1;             /* clear the TimerA timeout flag */

41.     TIMER1_CTL_R |= 0x01;           /* enable Timer A after initialization */

43.     for(i = 0; i < ttime; i++) {

44.         while ((TIMER1_RIS_R & 0x1) == 0)

45.             ;                       /* wait for TimerA timeout flag */

47.         TIMER1_ICR_R = 0x1;         /* clear the TimerA timeout flag */

48.     }

49. }