Cần giúp đỡ về giao tiếp 1-wire với ds1820

[notbadday]

Em đang viết 1 đoạn chương trình để hiển thị nhiệt độ lên LCD dùng cảm biến ds1820 và pic6f877a. Em đang gặp rắc rối trong việc giao tiếp với ds1820. Cụ thể là không hiện được nhiệt độ. Mấy anh xem giúp,có gì góp ý thì em cảm ơn rất nhiều.
Đây là code CCS, có mượn đoạn code phần LCD của bác nhh (hy vọng bác ko phản đối )

#include <16F877A.h>
#include <DEFS_16F877A.h>
#include <stdlib.h>

#fuses XT,NOWDT,NOPROTECT,NOLVP
#use delay(clock=4000000)
#define E  RD2
#define RS RD0
#define RW RD1
#define DQ RC0
#DEFINE TRISC 0x07
#byte lcd_data = 0x06   // Dia chi PORTB

/* Khai bao nguyen mau cac ham su dung */
byte lcd_read_byte();
void lcd_send_byte( byte address, byte n );
void lcd_init();
void lcd_gotoxy( byte x, byte y);
void lcd_putc( char c);
void lcd_refresh();
unsigned char ow_reset(void);
unsigned char read_bit(void);
void write_bit(char bival);
unsigned char read_byte(void);
void write_byte(char val);

/* Doc mot byte tu LCD */
byte lcd_read_byte()
{
   byte read_byte;
   set_tris_B(0xFF);       // PORTB = input
   RW = 1;
   delay_cycles(1);
   E  = 1;
   delay_cycles(1);
   read_byte = lcd_data;
   E  = 0;
   set_tris_B(0x00);       // PORTB = output
   return(read_byte);
}

/* Goi 1byte den LCD */
void lcd_send_byte( byte address, byte n )
{
   RS = 0;
   while ( bit_test(lcd_read_byte(),7) ) ;
   RS = address;
   delay_cycles(1);
   RW = 0;
   delay_cycles(1);
   E  = 0;
   lcd_data = n;
   delay_cycles(1);
   E = 1;
   delay_us(2);
   E = 0;
}

/* Khoi tao ban dau cho LCD */
void lcd_init()
{
    byte const lcd_init_string[4] = {0x38, 0x0C, 1 , 6};
    byte i;
    set_tris_B(0x00);
    RS = 0;
    RW = 0;
    E  = 0;
    delay_ms(15);
    for(i=1;i<=3;++i)
       {
         lcd_data = 3;
         delay_cycles(1);
         E = 1;
         delay_us(2);
         E = 0;
         delay_ms(5);
       }
    lcd_data = 2;
    delay_cycles(1);
    E = 1;
    delay_us(2);
    E = 0;
    delay_ms(5);
    for(i=0;i<=3;++i)
      {
         lcd_send_byte(0,lcd_init_string[i]);
      }
}

/* Nhay den vi tri (x,y) tren LCD,nhay nham y se bao loi */
void lcd_gotoxy( byte x, byte y)
{
   byte address;
   switch(y)
      {
         case 1:  address=0;
                  address+=x-1;
                  lcd_send_byte(0,0x80|address);
                  break;
         case 2:  address=0x40;
                  address+=x-1;
                  lcd_send_byte(0,0x80|address);
                  break;
         default :lcd_init();
                  lcd_putc("ERROR Y POSITION");
                  while(true); // Dung tai day!
      }
}

/* Hien thi ki tu hoac chuoi ra LCD */
void lcd_putc( char c)
{
   lcd_send_byte(1,c);
}

/* Hien thi ki tu hoac chuoi ra LCD */
void lcd_refresh()
{
   lcd_send_byte(0,1);
   lcd_send_byte(0,6);
}

//reset

unsigned char ow_reset(void)
{
      unsigned char presence;
      set_tris_C(0);
      DQ = 0; //pull DQ line low
      delay_us(500); // leave it low for at least 480us
      DQ = 1;         // allow line to return high
      delay_us(40);  // wait for presence
      set_tris_C(0x01);
      presence = DQ; // get presence signal
      delay_us(150); // wait for end of timeslot
      return(presence); // presence signal returned
}                            //     0=presence, 1 = no part

unsigned char read_bit(void)
{
      set_tris_C(0);
      DQ = 0; // pull DQ low to start timeslot
      delay_us(1);
      set_tris_C(0x01); //release DQ
      delay_us(15);       
      return(DQ); // return value of DQ line
}

void write_bit(char bitval)
{
      set_tris_C(0);
      DQ = 0; // pull DQ low to start timeslot
      delay_us(15);
      if(bitval==1)   set_tris_C(0x01); //release DQ      
      delay_us(50); // hold value for remainder of timeslot
}

// READ_BYTE - reads a byte from the one-wire bus.
//
unsigned char read_byte(void)
{
      unsigned char i;
      unsigned char value = 0;
      for (i=0;i<8;i++)
      {
         if(read_bit()) value|=0x01<<i;     // reads byte in, one byte at a time and then
                                                   // shifts it left
         delay_us(150); // wait for rest of timeslot
      }
      return(value);
}

void write_byte(char val)
{
      unsigned char i;
      unsigned char temp;
      for (i=0; i<8; i++)             // writes byte, one bit at a time
      {
         temp = val>>i;           // shifts val right 'i' spaces
         temp &= 0x01;               // copy that bit to temp
         write_bit(temp);            // write bit in temp into
      }
      delay_us(100);
}
/* Ham main */
void main (void)
{ 
   unsigned char  x;     
   set_tris_B(0);    //PORTB = output
   set_tris_D(0);    //PORTD = output   
   
   ow_reset();
   write_byte(0xCC); // skip ROM
   write_byte(0x44); // Start conversion
   
   delay_us(100);
   ow_reset();
   write_byte(0xCC);   
   x = read_byte();   
   lcd_init();
   lcd_gotoxy(5,1);
   printf(lcd_putc,"temp = %u",x);
   lcd_gotoxy(4,2);
   lcd_putc("PICVIETNAM!");
  }