//mega8 7.3728MHz gCC编译通过，_delay_us(us) _delay_ms(ms)调用库函数
//初始化把dq设置为输出
#define ds18b20_dq PC5
#define set_ds18b20_dq_ddr() DDRC|=1<#define set_ds18b20_dq() PORTC|=1<

#define clr_ds18b20_dq() PORTC&=~(1<#define clr_ds18b20_dq_ddr() DDRC&=~(1<#define in_ds18b20_dq() PINC&(1<
#define ds18b20_read_rom           0x33
#define ds18b20_match_rom          0x55
#define ds18b20_skip_rom           0xcc
#define ds18b20_search_rom         0xf0
#define ds18b20_alarm_search_rom   0xec
#define ds18b20_write_ram          0x4e
#define ds18b20_read_ram           0xbe
#define ds18b20_copy_ram           0x48
#define ds18b20_convert_tem        0x44
#define ds18b20_eecall_eeprom      0xb8
#define ds18b20_read_power_supply  0xb4
void reset_ds18b20(void)
{
clr_ds18b20_dq();
_delay_us(198);//100us
_delay_us(198);//100us
_delay_us(198);//100us
_delay_us(198);//100us
set_ds18b20_dq();
_delay_us(38);//20us
}
void ack_ds18b20(void)
{
while(in_ds18b20_dq());
    while(!(in_ds18b20_dq()));
_delay_us(38);//20us
}
uchar read_ds18b20(void)
{
uchar data=0;
uchar i=0;
for(i=0;i<8;i++)
{
data>>=1;
clr_ds18b20_dq();
_delay_us(1);//1us
set_ds18b20_dq();
_delay_us(2);//2us
if(in_ds18b20_dq()) data|=0x80;
_delay_us(118);//60us
}
return(data);
}
void write_ds18b20(uchar data)
{
uchar i=0;
for(i=0;i<8;i++)
{
if(data&0x01){
clr_ds18b20_dq();
_delay_us(14);//8us
set_ds18b20_dq();
_delay_us(108);//55us
}
else
{
clr_ds18b20_dq();
_delay_us(108);//55us
set_ds18b20_dq();
_delay_us(14);//8us
}
data>>=1;
} 
}
void convert_ds18b20(void)
{
reset_ds18b20();
    ack_ds18b20();
    _delay_ms(1);
    write_ds18b20(ds18b20_skip_rom);
    write_ds18b20(ds18b20_convert_tem);
}
void read_temperature(void)
{
reset_ds18b20();
ack_ds18b20();
_delay_ms(1);
write_ds18b20(ds18b20_skip_rom);
write_ds18b20(ds18b20_read_ram);
temperature_low=read_ds18b20();
temperature_high=read_ds18b20();
}