//DS18B20連接在端口C的第7引腳

//設置成輸入
#define DQ_INPUT DDRC &= ~(1 << PC7)    
//設置成輸出
#define DQ_OUT DDRC |= (1 << PC7)    
//設置成低電平
#define DQ_LO PORTC &= ~(1 << PC7)  
//設置成高電平
#define DQ_HI PORTC |= (1 << PC7)   
//讀出
#define DQ_R PINC & (1 << PC7)      

//中斷標志
unsigned char init_f;     

//延時函數
void s_10us(unsigned int ms)
{
    unsigned int aa;
	for(;ms>=1;ms--)
	{
	for(aa=0;aa<=17;aa++)
	{;}
	}
}	

//DS18B20復位
void ds1820_reset(void) 
{
 unsigned char i;
 //中斷保護
 init_f = SREG;    
 //關中斷
 CLI();      
 DQ_OUT;
 DQ_LO;
 s_10us(50);    //延時500us
 DQ_HI;
 DQ_INPUT;
 s_10us(8);     //延時80us
 i = DQ_R;
 s_10us(50);    //延時500us
 if (init_f & 0x80)  //恢復中斷狀態
  {   
  SEI();        
  }
}

//DS18B20字節讀取
unsigned char ds1820_read_byte(void) 
{
 unsigned char i;
 unsigned char value = 0;
 //中斷保護
 init_f = SREG;
 //關中斷    
 CLI();      
 for (i = 8; i != 0; i--) {
  value >>= 1;
  DQ_OUT;
  DQ_LO;
  s_10us(1);
  DQ_HI;
  DQ_INPUT;
  s_10us(1);
  if (DQ_R) {
   value|=0x80;
   }
  s_10us(5);   //延時60us
  }
 if (init_f & 0x80) //恢復中斷狀態
 {   
  SEI();
  }
 return(value);
}

//DS18B20字節寫入
void ds1820_write_byte(unsigned char value) 
{
 unsigned char i;
 //中斷保護
 init_f = SREG;   
 //關中斷 
 CLI();      
 for (i = 8; i != 0; i--) {
  DQ_OUT;
  DQ_LO;
  s_10us(1);
  if (value & 0x01) {
   DQ_HI;
   }
  s_10us(8);   //延時80us
  DQ_HI;     
  value >>= 1;
  }
 if (init_f & 0x80)//恢復中斷狀態
  {   
  SEI();
  }
}

//啟動ds1820轉換
void ds1820_start(void) 
{
 ds1820_reset();
 ds1820_write_byte(0xCC); //勿略ROM
 ds1820_write_byte(0x44); //啟動轉換
}

//讀溫度
unsigned int ds1820_read_temp(void)
 {
 unsigned int i;
 unsigned char buf[9];
 ds1820_reset();
 ds1820_write_byte(0xCC); //勿略ROM
 ds1820_write_byte(0xBE); //讀溫度
 for (i = 0; i < 9; i++) {
  buf[i] = ds1820_read_byte();
  }
 i = buf[1];
 i <<= 8;
 i |= buf[0];
 return i;
}