ds18b20+mega128 温度低于18度时就会显示0xff，为什么
18度以上是正常的，以下就不正常都是0xff，求解答！#include<avr/io.h>
#include<avr/interrupt.h>
#include<stdio.h>
/*************************************************************************
ds18b20头文件
M16内部8M
*************************************************************************/
#define CLR_DIR_1WIRE DDRC &= ~(1<<2); //只要修改这里的参数就可以了！呵呵！
#define SET_DIR_1WIRE DDRC |= (1<<2); //里面什么都不用该！
#define CLR_OP_1WIRE PORTC &= ~(1<<2);
#define SET_OP_1WIRE PORTC |= (1<<2);
#define CHECK_IP_1WIRE (PINC & 0x04) //检测
unsigned char wmh,wml;
void init_1820()
{
SET_DIR_1WIRE; //设置PC2 为输出
SET_OP_1WIRE;
CLR_OP_1WIRE;
delay_nus(550); //480us以上
SET_OP_1WIRE;
CLR_DIR_1WIRE;
delay_nus(20); //15~60us
while(CHECK_IP_1WIRE);
SET_DIR_1WIRE;
SET_OP_1WIRE;
delay_nus(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;
if(!(x&(1<<m)))
CLR_OP_1WIRE;
delay_nus(40);//15~60us
SET_OP_1WIRE;
}
SET_OP_1WIRE;
}
unsigned char read_1820()
{
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_nus(50); //60~120us
SET_DIR_1WIRE;
}
return (temp);
}
/*
uint8_t gettemp(void) //读取温度值
{
//unsigned char temh,teml,wm0,wm1,wm2,wm3,warnl,warnh;
uint8_t temh,teml,wm0,wm1,wm2,wm3,warnl,warnh;
init_1820(); //复位18b20
write_1820(0xcc);// 发出转换命令
write_1820(0x44);
delay_nms(880); //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();
warnl=read_1820();
warnh=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;
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使显示的低位
wml=(wm2%100)%10;
//int a;
//a=wmh;
//a=wml;
return wm2;
} */
unsigned int gettemp(void)
{
unsigned char tempL,tempH;
unsigned int x;
delay_1ms(); //等待1ms
init_1820();
write_1820(0xcc);//跳过ROM
write_1820(0xbe);//读数据
tempL=read_1820();
tempH=read_1820();
x=(tempH<<8)|tempL;
init_1820();
write_1820(0xcc);//跳过ROM
write_1820(0x44);//启动温度转换
return(x);
}
//延时程序：
//delay.h
/*-----------------------------------------------------------------------
延时函数
系统时钟：8M
-----------------------------------------------------------------------*/
void delay_1us(void) //1us延时函数
{
asm("nop");
}
void delay_nus(unsigned int n) //N us延时函数
{
unsigned int i=0;
for (i=0;i<n;i++)
delay_1us();
}
void delay_1ms(void) //1ms延时函数
{
unsigned int i;
for (i=0;i<1140;i++);
}
void delay_nms(unsigned int n) //N ms延时函数
{
unsigned int i=0;
for (i=0;i<n;i++)
delay_1ms();
}
没仔细看你代码，但是如果时序不正确的话，会出现问题 gzhmcu 发表于 2014-3-11 14:49
没仔细看你代码，但是如果时序不正确的话，会出现问题
晶振使用外部的和内部的会导致结果有差异么？ 内部的不是晶振，是RC...
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