18b20.c

利用DS18b20温度采集芯片通过AVR单片机采集温度

/**************************************
** Filename: 18b20.c
** Describe: 18b20 温度传感器
** Author ： 古欣 www.avrvi.com
** Time  :   2007-2-15
**************************************/

#include "config.h"

unsigned char wmh,wml,flag,count; //flag温度为负标志，count为实际温度
void init_1820(void)  
{  
    SET_DIR_1WIRE;      //设置PC2 为输出 
    SET_OP_1WIRE;   
    CLR_OP_1WIRE;  
    delay_us(480);    //480us以上  
    SET_OP_1WIRE;  
    CLR_DIR_1WIRE;  
    delay_us(20);     //15~60us  
    while(CHECK_IP_1WIRE);  
    SET_DIR_1WIRE;  
    SET_OP_1WIRE;  
    delay_us(140);   //60~240us  
}  
void write_1820(unsigned char x)  
{     
     unsigned char m;  
    for(m=0;m<8;m++)  
    {  
       CLR_OP_1WIRE;  
       if(x&(1<<m))    //写数据了，先写低位的！ 
       SET_OP_1WIRE;  
       else  
       {CLR_OP_1WIRE;}  
       delay_us(40);   //15~60us  
       SET_OP_1WIRE;  
    }  
     SET_OP_1WIRE;  
}  
unsigned char read_1820(void)  
{      
    unsigned char temp,k,n;  
    temp=0;  
    for(n=0;n<8;n++)  
    {
      CLR_OP_1WIRE;  
      SET_OP_1WIRE;  
      CLR_DIR_1WIRE;  
      k=(CHECK_IP_1WIRE);    //读数据,从低位开始  
      if(k)  
      temp|=(1<<n);  
      else  
      temp&=~(1<<n);  
      delay_us(50); //60~120us      
      SET_DIR_1WIRE;  
    }  
   return (temp);  
}   

void gettemp(void)         //读取温度值 
{  
     unsigned char temh,teml,wm0,wm1,wm2,wm3;  
     init_1820();        //复位18b20  
     write_1820(0xcc);   // 发出转换命令  
     write_1820(0x44); 
 //  delay_nms(800);     //不延时也好使，不知道怎么回事！ 
     init_1820();  
     write_1820(0xcc);  //发出读命令  
     write_1820(0xbe);  
     teml=read_1820();  //读数据  
     temh=read_1820();  
     wm0=teml>>4;       //只要高8位的低四位和低8位的高四位，温度范围0~99啦！ 
     wm1=temh<<4;
	 
//count=(temh*256+teml)*6.25;  //计算具体温度 	 
if((temh&0xF8) == 0xF8)  
{ 
   flag=1; 
   count=((0xFF-temh)*256+(0xFF-teml))*6.25; 
   //count=((0xFF-temh)*256+(0xFF-teml))*625; 
} 
else 
{    
   flag=0; 
   count=(temh*256+teml)*6.25; 
   //count=(temh*256+teml)*625; //计算具体温度  
}
     wm2=wm1+wm0;        //16进制转10进制 
     wm3=wm2/100; 
     wmh=(wm2%100)/10;   //出口参数了！wmh是显示的高位，wml是显示的低位 
     wml=(wm2%100)%10;
	 
	  
}