PIC16F877A Timer 2 and Interrupt

/*---------------------------------------------/
Name    : Mohd Syahri Fikri Bin Samusi

Pulse Generated using TIMER2
(interrupt) and switch RB4 interrupt

Date modified : 02 April 2012
/---------------------------------------------*/
#include <htc.h>
#include <stdio.h>
#include <pic16f877a.h>
#include <usart.c>
#define _XTAL_FREQ 20000000 // Set the oscillator frequency to 20MHz


void init_rs232()
{
    BRGH = 1;
    SPBRG = 129;    // set baud rate: Fosc=20Mhz, BR=9600
    TX9  = 0;   // ninebits?1:0,,,8- or 9-bit transmission
    SYNC = 0;   // asynchronous
    SPEN = 1;   // enable serial port pins
    TXEN = 1;   // enable the transmitter & (automatically)TXIF=1
    CREN = 1;   // enable reception
    SREN = 0;   // no effect
    TXIE = 0;   // disable tx interrupts
    RCIE = 0;   // disable rx interrupts
}


//--Interrupt Service function--
interrupt ISR(void) // Interrupt function definition
{
    //Interrupt TIMER2
    int a, b=1000;
    if (TMR2IF) // If the TMR2 Overflow flag is 1 (ie. TMR2 to PR2 match occurred), do .....
    {
        TMR2IE=0; // TMR2 Overflow Interrupt Disable
            RB2=!RB2; // Blinking the LED RB2

        for (a=0; a<b; a++)
        {
            PORTD=0;
        }

        for (a=b; a>0; a--)
        {
            PORTD=0x20;
        }

        TMR2IF=0; // Reset the TMR2 Overflow interrupt flag
        TMR2IE=1; // Re-enable TMR2 Overflow Interrupt
    }

    //Interrupt RB4
    int c;
    if(RBIF) // if RB port change interrupt flag
    {
        RBIE = 0; // Disable RB port change interrupt
        if(RB4)
        {
            c++;
            init_rs232();
            printf("Count up = %d \r\n", c);
        }

        RBIF = 0; // Reset RB port change interrupt flag
        RBIE = 1; // Re-enable RB port change interrupt
    }
    GIE=1;
}

//--Main Funtion--
void main(void)
{
    TRISC = 0x00; // Port C as outputs
    TRISB = 0xF0; // Port B as outputs/inputs
    TRISD = 0x00; // Port D as outputs
    //init_rs232();
    T2CON = 0b00001001;
    /*  Timer 2 control register
        TOUTPS3:TOUTPS0: Timer2 Output Postscale Select to 1:2
        T2CKPS1:T2CKPS0: Timer2 Clock Prescale Select to 4 */

    TMR2IE = 1; // Enable the TMR2 to PR2 match interrupt
    RBIE = 1;   // Enable the RB port change interrupt
    PR2 = 0xA0; // Timer0 Counter
    GIE = 1;    // Global interrupt enable
    TMR2IF = 0; // Clear TMR2 interrupt flag (no TMR2 to PR2 match occurred)
    RBIF = 0;   // Clear RB port change interrupt flag
    TMR2ON = 1; // Turn on Timer 2
    PEIE = 1;   // Peripheral Interrupt Enable

    while (1); //Run Run Run!
}
//End of Program