//mega128 8M晶振
const uchar CrcTable[256]=
{0, 94, 188, 226, 97, 63, 221, 131, 194, 156, 126, 32, 163, 253, 31, 65,
157, 195, 33, 127, 252, 162, 64, 30, 95, 1, 227, 189, 62, 96, 130, 220,
35, 125, 159, 193, 66, 28, 254, 160, 225, 191, 93, 3, 128, 222, 60, 98,
190, 224, 2, 92, 223, 129, 99, 61, 124, 34, 192, 158, 29, 67, 161, 255,
70, 24, 250, 164, 39, 121, 155, 197, 132, 218, 56, 102, 229, 187, 89, 7,
219, 133, 103, 57, 186, 228, 6, 88, 25, 71, 165, 251, 120, 38, 196, 154,
101, 59, 217, 135, 4, 90, 184, 230, 167, 249, 27, 69, 198, 152, 122, 36,
248, 166, 68, 26, 153, 199, 37, 123, 58, 100, 134, 216, 91, 5, 231, 185,
140, 210, 48, 110, 237, 179, 81, 15, 78, 16, 242, 172, 47, 113, 147, 205,
17, 79, 173, 243, 112, 46, 204, 146, 211, 141, 111, 49, 178, 236, 14, 80,
175, 241, 19, 77, 206, 144, 114, 44, 109, 51, 209, 143, 12, 82, 176, 238,
50, 108, 142, 208, 83, 13, 239, 177, 240, 174, 76, 18, 145, 207, 45, 115,
202, 148, 118, 40, 171, 245, 23, 73, 8, 86, 180, 234, 105, 55, 213, 139,
87, 9, 235, 181, 54, 104, 138, 212, 149, 203, 41, 119, 244, 170, 72, 22,
233, 183, 85, 11, 136, 214, 52, 106, 43, 117, 151, 201, 74, 20, 246, 168,
116, 42, 200, 150, 21, 75, 169, 247, 182, 232, 10, 84, 215, 137, 107, 53};
uchar CRC_OK1(uchar *p1,uchar num)
{
uchar OutData1;
uchar countbyte1;
OutData1=0;
for(countbyte1=1;countbyte1<num;countbyte1++)
{
OutData1=CrcTable[OutData1^*p1];
p1++;
}
p1-=(num-1);
return(OutData1);
}
void delay2(unsigned int x) //1.5us左右
{
while(x)
{
x--;
}
}
void init_1820(void)
{ DDRB|=0x04;
DS18B20_SET;
delay2(25); ///
DS18B20_CRL;
delay2(500); //480us以上
DS18B20_SET;
delay2(45); ///
DDRB&=~(1<<PB2);
delay2(40); //15~60us
while(PINB&(1<<PB2))
{
;
}
DDRB|=(1<<PB2);
DS18B20_SET;
delay2(160); //60~240us
}
void write_1820(unsigned char x)
{
unsigned char m;
for(m=0;m<8;m++)
{ DDRB|=(1<<PB2);
DS18B20_CRL;
if(x&(1<<m)) //写数据,从低位开始
DS18B20_SET;
else
DS18B20_CRL;
delay2(40); //15~60us
DS18B20_SET;
}
DS18B20_SET;
}
unsigned char read_1820(void)
{
unsigned char temp,k,n;
temp=0;
for(n=0;n<8;n++)
{ DDRB|=(1<<PB2);
DS18B20_CRL;
// delay(20); //
DS18B20_SET;
// delay(30); //
DDRB&=~(1<<PB2);
k=(PINB&(1<<PB2)); //读数据,从低位开始
if(k)
temp|=(1<<n);
else
temp&=~(1<<n);
delay2(80); //60~120us
DDRB|=(1<<PB2);
}
return (temp);
}
//读取温度
ReadTemperature()
{
unsigned char a=0;
unsigned char b=0;
unsigned int t=0;
static unsigned char ErrorT=0;
static unsigned int LastT;
init_1820(); //复位18b20
write_1820(0xcc); // 发出转换命令
write_1820(0x44);
delay2(400);
init_1820();
write_1820(0xcc); //发出读命令
write_1820(0xbe);
Buf18B20[0]=read_1820();
Buf18B20[1]=read_1820();
t=(unsigned int)((Buf18B20[1]*256+Buf18B20[0])); //计算具体温度
Buf18B20[2]=read_1820();
Buf18B20[3]=read_1820();
Buf18B20[4]=read_1820();
Buf18B20[5]=read_1820();
Buf18B20[6]=read_1820();
Buf18B20[7]=read_1820();
Buf18B20[8]=read_1820();
if((CRC_OK1(Buf18B20,10)!=0)||(Buf18B20[5]!=0xFF)) { if(ErrorT<10) ErrorT++; } else { if(ErrorT>0) ErrorT--; LastT=t; }
if(ErrorT==10) t=0x0640; else t=LastT; //传感器检测错误时,返回温度值100度
return(t);
} |