问MPLAB XC8编译器中存在延迟函数的问题

EN

#include <xc.h> // STANDARD INCLUDE FILE FOR MICROCHIP PRODUCTS

// uc CONFIG (START)

#pragma config FOSC = HS // 4MHz EXTERNAL CLOCK
#pragma config WTDE = ON
#pragma config PWRTE = OFF
#pragma config MCLRE = ON
#pragma config BOREN = ON
#pragma config LVP = ON
#pragma config CPD = OFF
#pragma config CP = OFF

// uC CONFIG (END)

#define _XTAL_FREQ 4000000
#define BT1 PORTA.RA0 // Button with number 1
#define BT2 PORTA.RA1 // Button with number 2
#define BT3 PORTA.RA2 // Button with number 3
#define BT4 PORTA.RA3 // Button with number 4

#define a PORTB.RB0 // "a" segment from 7-segment display
#define b PORTB.RB1 // "b" segment from 7-segment display
#define c PORTB.RB2 // "c" segment from 7-segment display
#define d PORTB.RB3 // "d" segment from 7-segment display
#define e PORTB.RB4 // "e" segment from 7-segment display
#define f PORTB.RB5 // "f" segment from 7-segment display
#define g PORTB.RB6 // "g" segment from 7-segment display

void main ()
{
  TRISA = 0x01;
  TRISB = 0x00;
  PORTA = 0x00;
  PORTB = 0x00;

  while(1)
  {
     if (BT1 == 1)
     {
       a = 0x00;
       b = 0x01;
       c = 0x01;
       d = 0x00;
       e = 0x00;
       f = 0x00;
       g = 0x00;
       _delay_ms(5000);
       a = 0x00;
       b = 0x00;
       c = 0x00;
       d = 0x00;
       e = 0x00;
       f = 0x00;
       g = 0x00;
      _delay_ms(1000);  
    }    
  }
}