Single bus driver (DS18B20)

sbit DQ=P3^7; //DS18B20 data transmission line connects to the corresponding pin of the microcontroller

void delaymm(uint z)

{

     uint x,y;

     for(x=z;x>0;x--)

     for(y=110;y>0;y--);

}

 //Read one byte of data from DS18B20, starting from the low bit

ReadOneChar(void)       

{

     unsigned char i=0;         

     unsigned char dat=0;

    for (i=8;i>0;i--)      

         {

                 DQ=1;

                delay(1);

                DQ=0;     

                dat>>=1; //Shift the read value to the left by one bit to form a byte

                DQ=1;

            if(DQ)

              dat|=0x80; //If the highest DQ is 1, the highest position is 1

         delay(4);

         }

    return(that);

}

//Write one byte of data to DS18B20, starting from the lowest bit

void WriteOneChar(unsigned char dat) 

{

     unsigned char i=0;         

     for(i=8;i>0;i--) 

     {

         DQ=0;   

         DQ=dat&0x01; //If the lowest bit is 1, write 1

         delay(5);

         DQ=1;

         dat>>=1; //Shift left by one bit, for example, i = 8, after comparison, it is consistent, i = 7 is the first shift left by one bit, so that the second bit is compared in the next cycle & 0X01

     }

     delay(4);

}

void Init_DS18B20(void)/*Function: DS18B20 initialization subroutine*/

{

     unsigned char x=0;

     DQ=1; //DQ is set high first

     delay(8); //delay

     DQ=0; //Send reset pulse

     delay(85); //delay (>480ms)

     DQ=1; //Pull up the data line

     delay(14); //wait (15~60ms)

}

//Function: Read temperature value from DS18B20

ReadTemperature(void) 

{ 

     Init_DS18B20(); //Initialization

     WriteOneChar(0xcc); //Skip the operation of reading the serial number

     WriteOneChar(0x44); //Start temperature conversion

     delaymm(125); //The conversion takes a little time, delay

     Init_DS18B20(); //Initialization

     WriteOneChar(0xcc); //Skip the operation of reading the serial number

     WriteOneChar(0xbe); //Read the temperature register (the first two values ​​are the low and high bits of the temperature respectively)

     delaymm(125);

     tempL=ReadOneChar(); //Read the low LSB of the temperature

     tempH=ReadOneChar(); //Read the high MSB of temperature 

     //Temperature conversion, convert the high and low bits into actual temperature

     temperature=((tempH*256)+tempL)*0.0625;

     delay(200);

     return(temperature);

}