Example of reading temperature sensor DS18B20

Configuring the IO Pin

#define DS18B20         BIT4                      //Configure IO pin
#define Ds18b20_high    p2out |= BIT4
#define Ds18b20_low     p2out &= ~BIT4

precise delay macro code

#define Cpu_clock       8000000UL               //mclk is set to 8MHz                
#define DELAY_US (US)    __delay_cycles (cpu_clock/1000000 * (US))
#define Delay_ms (ms)    __delay_cycles (cpu_clock/1000* (MS))

Find a table of binary fractional parts

const int n16tab[16]={      //used for binary fractional parts look up table
    0,
    625,
    1250,
    1875, 2500,
    3125,
    3750,
    4375,
    5625,
    6250,
6875, 7500, 8125, 8750, 9375} ;

Reset

/* ********************************************************************** * Name: ds18b20_init () * Function: RESET DS18B20 * Entry parameter: None * Export parameters: The existence of a, 0--does not exist * Description: Need to configure IO, software delay to accurate * Example: no *********************************************************************
        * */char Ds18b20_reset (void) {int i;
        Char e;                       -------Low-----------------------------------p2dir |= Ds18b20;                            configured as output ds18b20_low;          Pull down//-------wait more than 480 microseconds----------------------------Delay_us (540);                      Wait less than 480 microseconds//-------Pull high-----------------------------------p2dir &= ~ds18b20;                        Configured as input P2ren |=ds18b20;                           Enable resistor Ds18b20_high;

        Pull//-------Wait 15 microseconds---------------------------------Delay_us (15);
        -------detection exists-------------------------------------------i=0;
        e=0;
   while (1) {         if ((p2in & Ds18b20) ==0) {e=1; 
            Break
            } delay_us (1);
            i++;   
            if (i>60) {break;
        }}//------------delay more than 480 microseconds---------------------------------Delay_us (500);
return e;  }

Read bytes

/* ********************************************************************** * Name: ds18b20_readbyte () * Function: Read bit * entry parameter: none * Exit parameters: Returns a byte read back from Ds18b20 * Description: Need to configure IO, software delay to accurate * Example: no *****************************************************************
    */unsigned char ds18b20_readbyte (void) {unsigned char i,retd=0;               for (i=0;i<8;i++)//bit-count value {retd>>=1;        Move right, ready to accept the new data bit//-------pull down bus 5 microseconds--------------------------P2dir |=ds18b20;            configured as output ds18b20_low;        Pull low, start reading data bit Delay_us (5);      Wait 5 microseconds//-------release bus-----------------------------------p2dir &= ~ds18b20;        Configured as input P2ren |=ds18b20;           Enable resistor Ds18b20_high;       Pull//-------Wait 15 microseconds-----------------------------Delay_us (15);
            Wait 15 microseconds//-------Check if the bit is high-----------------------if (P2IN&AMP;DS18B20)//The bit is high {     retd|=0x80; is to have this locationHigh}//-------Wait 42 microseconds-----------------------------Delay_us (42);                Wait 42 microseconds} return retd; Returns a byte read to}

Write Bytes

/* ********************************************************************** * Name: ds18b20_writebyte () * Function: Writing section * Entry parameter: none * Export parameters: No * Description: Need to configure IO, software delay to accurate * Example: no ********************************************************************** */void DS18

    B20_writebyte (unsigned char wrd) {unsigned char i; for (i=0;i<8;i++)//bit count value {if (WRD&AMP;0X01)///This bit data is high {//-----        --Pull down bus 5 μs--------------------------P2dir |=ds18b20;  
              configured as output ds18b20_low;

              Delay_us (5); -------Pull-up bus 60 μs----------------------------------p2dir &= ~ds18b20;//configured as input P2ren |=DS18  B20;     Enable resistor Ds18b20_high;
        Pull-up Delay_us (60);  } else {//-------pull down bus 60 microseconds----------------------------------P2dir |=ds18b20;      configured as output ds18b20_low;

        is low, the single bus is pulled low delay_us (60);      -------Pull-up bus 5 μs-----------------------------------p2dir &= ~ds18b20;//configured as input P2ren  |=ds18b20;     Enable resistor Ds18b20_high;
        Pull-up Delay_us (5);

        }//-------wait more than 1 microseconds-------------------------------Delay_us (2);                -------Move right 1-bit-------------------------------------wrd>>=1; Move right to prepare for writing new bits of Data}}

Reading temperature

A complete read temperature flow.

/* ********************************************************************** * Name: ds18b20_readtemp () * Function: Read temperature * entry parameter: none * Exit Parameters: Return Temperature Value * Description: Need to configure IO, software delay to accurate * Example: no ********************************************************************** */char E
;
    int ds18b20_readtemp () {unsigned char buff[9];
    unsigned char i;

    unsigned char a,b,c;
    ------MCLK is set to 8MHz------------Dcoctl=caldco_8mhz;

    Bcsctl1=calbc1_8mhz;          E=ds18b20_reset ();        initialization, each write command starts from initialization ds18b20_writebyte (0XCC);        Skip ROM Ds18b20_writebyte (0x44);                  Starting temperature Conversion Delay_ms (750);              Delay 750us E=ds18b20_reset ();        initialization, each write command starts from initialization ds18b20_writebyte (0XCC);        Skip ROM Ds18b20_writebyte (0xbe);   Read-in register command//-----Read 9 consecutive-----------------for (i=0;i<9;i++) {buff[i]=ds18b20_readbyte ();
    Read Register}/*/---------Calculate temperature----------------------------------------------------a=buff[0]&0x0f; if ((buff[1]&AMP;0X80)! = 0) {a=~a;
            a=a&0x0f;
    A+=1;      } *fdat=n16tab[a];
    Get the b=buff[0]>>4; of the decimal part
    c=buff[1]<<4;
    C|=b;              *idat=c;
    Get the integer part *//-----MCLK set to 1MHz-----------Dcoctl=caldco_1mhz;

    Bcsctl1=calbc1_1mhz;
Return ((int*) buff) [0]; }

calculate the temperature value

By binary data, get the integer part Idat, fractional part fdat.

void calc_temp (int hex,char *idat,int *fdat)
{
    unsigned char a,b,c;
    char Hi,lo;
    Lo=hex;
    hi=hex>>8;
    ---------Calculate temperature----------------------------------------------------
    a=lo&0x0f;
    if ((hi&0x80)! = 0)
    {
        a=~a;
        a=a&0x0f;
        a+=1;
    }
    *fdat=n16tab[a];      Get the

    b=lo>>4;
    of the decimal part c=hi<<4;
    c|=b;
    *idat=c;              Get the integer part
}