Timer1 on PIC24F16KA102 don't work

Question

I want to configure timer1 of PIC24F16KA102 to count it. The clock source must be the internal clock of 8 MHz. I configured the register T1CON and set on high level the bit TON to start the timer. Timer1 is set to go in overflow every 100 us, then with a while cycle I wille increase the variable count. I'am not understanding because timer1 don't work, I observed that it does not increase. Why?

   #include <xc.h>
   #include "config.h"

   int count = 0;

   void main(void) {

        TRISB = 0;    

        T1CON = 0;      //TRM1 stopped, internal clock source, prescaler 1:1

        _TON = 1;
        TMR1 = 65135;   //overflow of TM1 every 100 us (400 counts)

        while (1) {

             if (TMR1 == 65535) {

             count++;       // increase every 100 us
             TMR1 = 65135;

             }

        }
   }

K_Trenholm · Answer 1 · 2017-11-20T17:17:52.617

Try setting the Timer 1 period register (PR1) and using an interrupt rather than trying to catch and reload TMR1 on its final count. You're trying to catch TMR1 on EXACTLY 65535, and that will almost never work because once TMR1 hits 65535, it's just going to overflow and begin counting from 0 again. EDIT: Of course, this assumes it counts at all. I don't know what the behavior of a timer is when you leave the period register at 0. It may simply count to it's maximum of 65535 then reset to 0, or it may never count at all and continuously load PRx into TMRx since they match at 0

PRx is meant to define the period you want for a given timer, in this case 100uS. PR1 = 400. Once TMR1 = PR1, the timer will reset itself automatically and raise an interrupt to alert you that the timer has elapsed.

volatile unsigned int count = 0;   //Vars that change in an ISR should be volatile
PR1 = 400;          //Set Period for Timer1 (100us)
T1CON = 0x8000;     //Enable Timer1

IEC0bits.T1IE = 1;      //Enable Timer1 Interrupt
IPC0bits.T1IP = 0b011;

Pair this with an ISR function to increment count whenever the timer elapses:

void __attribute__ ((interrupt,no_auto_psv)) _T1Interrupt (void)
{
 count++;
 IFS0bits.T1IF = 0;  //Make sure to clear the interrupt flag
}

You could also try something like this without any interrupts:

void main(void){
unsigned int count = 0;
TMR1 = 0;
T1CON = 0x8000;   //TON = 1

    while(1){
         if (TMR1 >= 400){
          count++;
          TMR1=0;
         }
    }
}

However I would recommend using the PR register and an ISR. This is what it's meant to do.

EDIT: I would also recommend reading the PIC24F Reference Manual on timers: Here

Timer1 on PIC24F16KA102 don't work

1 Answers1