ds18b20.h

很适用的PS/2源程序,欢迎大家下载. 目前比较流行

#include <at89x52.h>
#define ds18b20_p P3_0
extern unsigned int temperature(void);

/*************************************************************
   Notice:if divided by 16 is temperature!
   Made or rework by wangwudong at 2005\8\1
*************************************************************/
void ds18b20_delay(unsigned int useconds)
{
  for(;useconds>0;useconds--);
}
unsigned char ds18b20_reset(void){
  unsigned char presence;
  ds18b20_p  = 0;
  ds18b20_delay(35);
  ds18b20_p  = 1;
  ds18b20_delay(4);
  presence = ds18b20_p ;
  ds18b20_delay(25);
  return(presence);
}
unsigned char ds18b20_read(void){
  unsigned char i;
  unsigned char value = 0;
  for (i=8;i>0;i--)  {
    value>>=1;
    ds18b20_p  = 0;
    ds18b20_p  = 1;
    i=i;
    i=i;
    i=i;
    if(ds18b20_p )value|=0x80;
    ds18b20_delay(6);
  }
  return(value);
}


void ds18b20_write(char val){
  unsigned char i;
  for (i=8; i>0; i--) {
    ds18b20_p  = 0;
    ds18b20_p  = val&0x01;
    ds18b20_delay(5);
    ds18b20_p  = 1;
    val=val/2;
  }
  ds18b20_delay(5);
}
unsigned int temperature(void){
  union{unsigned char c[2];
  unsigned int x;
  }temp;
  ds18b20_reset();
  ds18b20_write(0xCC); // Skip ROM
  ds18b20_write(0xBE); // Read Scratch Pad
  temp.c[1]=ds18b20_read();
  temp.c[0]=ds18b20_read();
  ds18b20_reset();
  ds18b20_write(0xCC); //Skip ROM
  ds18b20_write(0x44); // Start Conversion
  return temp.x;
}