Creating 1Hz pulse using PIC internal timer interrupt

pic16f877a has 3 timers. they are: - Timer0 (8 bit) - Timer1 (16 bit) - Timer2 (8bit)

1. Setting Up Timer1 OPTION_REG register

• Set prescale of 8

    T1CKPS0 = 1;
    T1CKPS1 = 1;

- Enable Timer1

    TMR1ON = 1;

2. Set up the Interrupt INTCON register

• Enable Global an Peripheral interrupt

    GIE = 1; // enable global interrupt
    PEIE = 1; // enable peripheral interrupt

• Enable Timer1 overflow interupt

    TMR1IE = 1; // enable timer1 overflow interrupt

• Clear the interrupt flag initially

    TMR1IF = 0; // clear timer1 overflow interrupt flag

3. Timer value calculation for the desired delay

• RegValue = 65536-((Delay * Fosc)/(Prescalar*4))

    TMR1H=0x9E;     // Load the time value(0xBDC) for 100 milli delay
    TMR1L=0x58;

4. Writing the Interrupt Service Routine ISR

• Clear overflow interrupt flag
• Reset timer value

void  __interrupt() isr(void) {
    if(TMR1IF==1) {
        TMR1H=0x9E;     // Load the time value(0xBDC) for 100 milli delay
        TMR1L=0x58;
        TMR1IF=0; // reset overflow flag
        count++; // counter increments every 100 milli
    } 
    return;
}

Circuit Diagram:

License

This work is licensed under GNU General Public License v3.0.