#int_EXT
void  EXT_isr(void) 
{
   pulses++;
}
.
.
.
void main()
{
   pulses = 0;

   .
   .......PIC initialization code.........
   .
   ext_int_edge( H_TO_L ); //track high to low transitions on pin
   enable_interrupts(INT_EXT);// enable external interrupt
   enable_interrupts(GLOBAL);

   set_tris_b(0xff);
   while(true)
   {
      printf("pulses: %u\r\n",pulses);
      delay_ms(500);
   
   }


}

#include <16F877A.h>
#device adc=8

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES HS                       //High speed Osc (> 4mhz)
#FUSES NOPUT                    //No Power Up Timer
#FUSES NOPROTECT                //Code not protected from reading
#FUSES NODEBUG                  //No Debug mode for ICD
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOLVP                    //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOCPD                    //No EE protection
#FUSES NOWRT                    //Program memory not write protected

#use delay(clock=20000000)
#use rs232(baud=57600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8)
#use fast_io (B)

volatile unsigned int x;

#int_EXT
void  EXT_isr(void) 
{
   disable_interrupts(INT_EXT);
   
   x++;
   
   clear_interrupt(INT_EXT);
   enable_interrupts(INT_EXT);
}


void main()
{
   x =0;
   setup_adc_ports(NO_ANALOGS);
   setup_adc(ADC_OFF);
   setup_psp(PSP_DISABLED);
   setup_spi(SPI_SS_DISABLED);
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
   setup_timer_1(T1_DISABLED);
   setup_timer_2(T2_DISABLED,0,1);
   setup_comparator(NC_NC_NC_NC);
   setup_vref(FALSE);
   enable_interrupts(INT_EXT);
   enable_interrupts(GLOBAL);
   port_b_pullups (false);
   
   while(1)
   {
   
      printf("%u\r\n",x); 
      delay_ms(1000);
   
   }

}