关于pic程序单片机的问题

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/*
  Project: Measuring heart rate through fingertip
  Copyright @ Rajendra Bhatt
  January 18, 2011
  PIC16F628A at 4.0 MHz external clock, MCLR enabled
*/

***it IR_Tx at RA3_bit;
***it DD0_Set at RA2_bit;
***it DD1_Set at RA1_bit;
***it DD2_Set at RA0_bit;
***it start at RB7_bit;
unsigned short j, DD0, DD1, DD2, DD3;
unsigned short pulserate, pulsecount;
unsigned int i;
//-------------- Function to Return mask for common anode 7-seg. display
unsigned short mask(unsigned short num) {
switch (num) {
case 0 : return 0xC0;
case 1 : return 0xF9;
case 2 : return 0xA4;
case 3 : return 0xB0;
case 4 : return 0x99;
case 5 : return 0x92;
case 6 : return 0x82;
case 7 : return 0xF8;
case 8 : return 0x80;
case 9 : return 0x90;
} //case end
}

void delay_debounce(){
Delay_ms(300);
}

void delay_refresh(){
Delay_ms(5);
}

void countpulse(){
IR_Tx = 1;
delay_debounce();
delay_debounce();
TMR0=0;
Delay_ms(15000);  // Delay 1 Sec
IR_Tx = 0;
pulsecount = TMR0;
pulserate = pulsecount*4;
}

void display(){
  DD0 = pulserate%10;
  DD0 = mask(DD0);
  DD1 = (pulserate/10)%10;
  DD1 = mask(DD1);
  DD2 = pulserate/100;
  DD2 = mask(DD2);
  for (i = 0; i<=180*j; i++) {
    DD0_Set = 0;
    DD1_Set = 1;
    DD2_Set = 1;
    PORTB = DD0;
    delay_refresh();
    DD0_Set = 1;
    DD1_Set = 0;
    DD2_Set = 1;
    PORTB = DD1;
    delay_refresh();
    DD0_Set = 1;
    DD1_Set = 1;
    DD2_Set = 0;
    PORTB = DD2;
    delay_refresh();
    }
  DD2_Set = 1;
}

void main() {
CMCON = 0x07;    // Disable Comparators
TRISA = 0b00110000; // RA4/T0CKI input, RA5 is I/P only
TRISB = 0b10000000; // RB7 input, rest output
OPTION_REG = 0b00101000; // Prescaler (1:1), TOCS =1 for counter mode
pulserate = 0;
j = 1;
display();
do {
  if(!start){
   delay_debounce();
   countpulse();
   j= 3;
   display();
  }
} while(1);  // Infinite loop
}