51单片机学习--DS18B20温度读取温度报警器

需要先编写OneWire模块，再在DS18B20模块中调用OneWire模块的函数

先根据原理图做好端口的声明：

sbit OneWire_DQ = P3^7;

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接下来像之前一样把时序结构用代码模拟出来：

unsigned char OneWire_Init(void)
{unsigned char i;unsigned char AckBit;OneWire_DQ = 1;OneWire_DQ = 0; //总线拉低//延时500usi = 227; while (--i);OneWire_DQ = 1; //释放总线//延时70usi = 29; while (--i);AckBit = OneWire_DQ;//延时500usi = 227; while (--i);return AckBit;
}

---

void OneWire_SendBit(unsigned char Bit)
{unsigned char i;OneWire_DQ = 0; //总线拉低//延时10us后直接读电平i = 4; while(--i);OneWire_DQ = Bit;//延时50us凑满时间片i = 22; while(--i);OneWire_DQ = 1;
}

---

unsigned char OneWire_ReceiveBit(void)
{unsigned char i;unsigned char Bit;OneWire_DQ = 0;//延时5usi = 2; while(--i);OneWire_DQ = 1;//延时5usi = 2; while(--i);Bit = OneWire_DQ;//延时50usi = 22; while(--i);return Bit;
}

---

void OneWire_SendByte(unsigned char Byte)
{unsigned char i;for(i = 0; i < 8; i ++) {OneWire_SendBit(Byte & (0x01<<i));}
}unsigned char OneWire_ReceiveByte(void)
{unsigned char i;unsigned char Byte = 0x00;for(i = 0; i < 8; i ++) {if(OneWire_ReceiveBit()) {Byte |= (0x01<<i);}}return Byte;
}

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至此，OneWire模块就写好了，接下来在DS18B20模块中模拟数据帧：

#include <REGX52.H>
#include "OneWire.h"#define DS18B20_SKIP_ROM   0xCC
#define DS18B20_CONVERT_T  0x44
#define DS18B20_READ_SCRATCHPAD  0xBEvoid DS18B20_ConvertT(void)
{OneWire_Init();OneWire_SendByte(DS18B20_SKIP_ROM);OneWire_SendByte(DS18B20_CONVERT_T);
}float DS18B20_ReadT(void)
{unsigned char TLSB, TMSB;int temp;float T;OneWire_Init();OneWire_SendByte(DS18B20_SKIP_ROM);OneWire_SendByte(DS18B20_READ_SCRATCHPAD);TLSB = OneWire_ReceiveByte();TMSB = OneWire_ReceiveByte();temp = (TMSB<<8) | TLSB;T = temp / 16.0;return T;
}

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之后只需要在main中调用即可

#include <REGX52.H>
#include "LCD1602.h"
#include "DS18B20.h"float T;void main()
{LCD_Init();LCD_ShowString(1, 1, "Temperature!");while(1){DS18B20_ConvertT();T = DS18B20_ReadT();if(T < 0){LCD_ShowChar(2, 1, '-');T = -T;}else{LCD_ShowChar(2, 1, '+');}LCD_ShowNum(2, 2, T, 3);//整数部分LCD_ShowChar(2, 5, '.');LCD_ShowNum(2, 6, (unsigned long)(T *10000) % 10000, 4); //小数部分}
}

---

接下来进行一些综合的应用：温度报警器，按键可调整报警温度的上下限，且能用AT24C02记录上下限，掉电不丢失（这里默认所有温度不会超过DS18B20的芯片范围）

#include <REGX52.H>
#include "LCD1602.h"
#include "DS18B20.h"
#include "Delay.h"
#include "AT24C02.h"
#include "Key.h"
#include "Timer0.h"float T, TShow;
char THigh, TLow;
unsigned char KeyNum;void main()
{THigh = AT24C02_ReadByte(0);TLow = AT24C02_ReadByte(1);//第一次读可能是非法值，所以要特判一下if(THigh > 125 || TLow < - 55 || THigh <= TLow){THigh = 20;TLow = 15;}Timer0_Init();LCD_Init();LCD_ShowString(1, 1, "T:");LCD_ShowString(2, 1, "TH:");LCD_ShowString(2, 9, "TL:");LCD_ShowSignedNum(2, 4, THigh, 3);LCD_ShowSignedNum(2, 12, TLow, 3);while(1){KeyNum = Key();/*温度读取及显示*/DS18B20_ConvertT();T = DS18B20_ReadT();if(T < 0){LCD_ShowChar(1, 3, '-');TShow = -T;}else{LCD_ShowChar(1, 3, '+');TShow = T;}LCD_ShowNum(1, 4, TShow, 3);LCD_ShowChar(1, 7, '.');LCD_ShowNum(1, 8, (unsigned long)(TShow * 100)%100, 2);/*阈值判断及显示*/if(KeyNum){if(KeyNum == 1) THigh ++;if(KeyNum == 2) THigh --;if(KeyNum == 3) TLow ++;if(KeyNum == 4) TLow --;LCD_ShowSignedNum(2, 4, THigh, 3);LCD_ShowSignedNum(2, 12, TLow, 3);AT24C02_WriteByte(0, THigh);Delay(5);AT24C02_WriteByte(1, TLow);Delay(5);}if(T > THigh) LCD_ShowString(1, 13, "OV:H");else if(T < TLow) LCD_ShowString(1, 13, "OV:L");else LCD_ShowString(1, 13, "    ");}
}void Timer0_Routine() interrupt 1
{static unsigned int T0Count;TL0 = 0x66;		//设置定时初值TH0 = 0xFC;		//设置定时初值T0Count ++;if(T0Count >= 20) //20ms执行一次{T0Count = 0;Key_Loop();}
}

这还没完，在与定时器的结合中，定时器的中断会影响OneWire的延时，从而影响其中的时序结构进而影响温度实时获取，所以在时序结构编写的代码中需要加上屏蔽定时器中断的代码：开始时加上EA = 0,最后加上EA = 1，改版后的OneWire模块如下：

#include <REGX52.H>sbit OneWire_DQ = P3^7;unsigned char OneWire_Init(void)
{unsigned char i;unsigned char AckBit;EA = 0;  //屏蔽中断OneWire_DQ = 1;OneWire_DQ = 0; //总线拉低//延时500usi = 227; while (--i);OneWire_DQ = 1; //释放总线//延时70usi = 29; while (--i);AckBit = OneWire_DQ;//延时500usi = 227; while (--i);EA = 1;return AckBit;
}void OneWire_SendBit(unsigned char Bit)
{unsigned char i;EA = 0;  //屏蔽中断OneWire_DQ = 0; //总线拉低//延时10us后直接读电平i = 4; while(--i);OneWire_DQ = Bit;//延时50us凑满时间片i = 22; while(--i);OneWire_DQ = 1;EA = 1;
}unsigned char OneWire_ReceiveBit(void)
{unsigned char i;unsigned char Bit;EA = 0;  //屏蔽中断OneWire_DQ = 0;//延时5usi = 2; while(--i);OneWire_DQ = 1;//延时5usi = 2; while(--i);Bit = OneWire_DQ;//延时50usi = 22; while(--i);EA = 1;return Bit;
}void OneWire_SendByte(unsigned char Byte)
{unsigned char i;for(i = 0; i < 8; i ++) {OneWire_SendBit(Byte & (0x01<<i));}
}unsigned char OneWire_ReceiveByte(void)
{unsigned char i;unsigned char Byte = 0x00;for(i = 0; i < 8; i ++) {if(OneWire_ReceiveBit()) {Byte |= (0x01<<i);}}return Byte;
}

但是这样虽然能维护好单总线的通信，但这样直接屏蔽中断却会影响定时器的计时准确度，从而对定时器控制的其他模块造成影响，这也就是单总线的一大缺点，不过在这个实例中，按键的定时器准度要求并不高，所以这样控制影响不大