Hardware Timer

01: /* timer3.c
02:  *
03:  *  Use timer1 to blink an LED
04: */
05: 
06: #include <plib.h>
07: 
08: void wait();
09: 
10: #define LED1 BIT_0  // LED1 is connected to RD0
11: 
12: 
13: int main()
14: {
15:         int i;
16:         mPORTDSetPinsDigitalOut(LED1);   /* Make LED1 output */
17:         mPORTDClearBits(LED1);      /* Turn off LED1 on startup */
18:         while (1) {
19:                 mPORTDToggleBits(LED1);     /* Toggle LED1 */
20:                 wait();
21:         }
22:         return 0;
23: }
24: 
25: void wait()
26: {
27:         const int DLY = 36000;
28:         T1CON = 0x30; // turn timer off and set prescaller to 1:256
29:         TMR1 = 0;
30:         PR1 = 0xFFFF;
31:         T1CONSET = 0x8000; // start timer
32:         while (TMR1 < DLY) {
33:                 // just wait
34:         }
35:         T1CONCLR = 0x8000; // stop timer
36: }

Results

I timed my LED over ten cycles and got 18.37 seconds. According to my calculation that is equivalent to a PB clock rate of 10.03 MHz.

Exercise