#include    <pic.h>

__CONFIG(WDTDIS & XT & UNPROTECT & LVPDIS);

#define XTAL    4000000         // crystal frequency - 4MHz


long tics = 0l;
int flag = 1;

void interrupt prv_int(void)
{
    if (!TMR2IF)
       return;

    //****************************************************************
    // TMR2IF is 1 when the counter TMR2 is arrived to the
    // PR2 register value (default: 0xFF = 255)
    // so to calculate when will enter here:
    //
    // Freq = (clock cycle / 4 / 16 / 255 / 16 = 15Hz
    // Period = 1 / 15Hz = 65msec
    //****************************************************************

    TMR2IF = 0;

    tics++;

    if (tics == 15l)
    {
        tics = 0l;

        //***********************************************************
        // To calculate when will enter here:
	// Freq = 15Hz / 15 = 1Hz and periord is 1 second
        //******************************+****************************
       
        if (flag == 1)
        {
            RB5 = 1;
            flag = 0;
        }
        else
        {
            RB5 = 0;
            flag = 1;
        }
    }
}

main()
{
    TRISB  = 0b11000000;
    CMCON  = 0b00000111;    // disable comparator on ra0,1,2
    TRISA  = 0b11111111;


    //******************************************************
    // The following lines set the T2CON control register

    TOUTPS3 = 1;  // these are the 6,5,4,3 bits of the
    TOUTPS2 = 1;  // control register T2CON and set
    TOUTPS1 = 1;  // the postscale value
    TOUTPS0 = 1;  //

    TMR2ON  = 1;  // this enable the Timer2

    T2CKPS1 = 1;  // these are the 1 and 0 bits of the
    T2CKPS0 = 1;  // control register T2CON and set the
    		  // prescale value

    // Is also possible set the bits of T2CON control register
    // with a unique comand like the following:
    //
    // T2CON  = 0x7E;	
    //
    // here the hexadecimal value 7E means
    // 76543210
    //  1111110 
    //  1111    -> postscale value 1:16
    //      1   -> enable timer2
    //       1x -> prescaler value 1:16
    //******************************************************

    TMR2IE = 1;	// TMR2 to PR2 enable match interrupt
    // PR2 = 0xFF; default value

    INTCON = 0;  // reset all the flag bits for all the interrupts
    PEIE = 1;	// peripheral interrupt enable bit
    GIE  = 1;	// global interrupt enable bit (1: enable all)

    while(1)
        continue;    // while forewer
}