ds18b20.c

51系列单片机的温度传感器项目代码

//clock=11.0592MHz
#include <REG52.H>
#include <string.h>
#include "stdio.h"

typedef unsigned int word;
sbit DQ = P1^0;

void delay (word useconds)
{
	for(;useconds>0;useconds--);
}

//////////////////////////////////////////////////////////////////////////////
// OW_RESET - performs a reset on the one-wire bus and
// returns the presence detect. Reset is 480us, so delay
// value is (480-24)/16 = 28.5 - we use 29. Presence checked
// another 70us later, so delay is (70-24)/16 = 2.875 - we use 3.
//
unsigned char ow_reset(void)
{
	unsigned char presence;
	DQ = 0; //pull DQ line low
	delay(29); // leave it low for 480us
	DQ = 1; // allow line to return high
	delay(3); // wait for presence
	presence = DQ; // get presence signal
	delay(25); // wait for end of timeslot
	return(presence); // presence signal returned
} // 0=presence, 1 = no part

//////////////////////////////////////////////////////////////////////////////
// READ_BIT - reads a bit from the one-wire bus. The delay
// required for a read is 15us, so the DELAY routine won't work.
// We put our own delay function in this routine in the form of a
// for() loop.
//
unsigned char read_bit(void)
{
	unsigned char i;
	DQ = 0; // pull DQ low to start timeslot
	DQ = 1; // then return high
	for (i=0; i<3; i++); // delay 15us from start of timeslot
	return(DQ); // return value of DQ line
}

//////////////////////////////////////////////////////////////////////////////
// WRITE_BIT - writes a bit to the one-wire bus, passed in bitval.
//
void write_bit(char bitval)
{
	DQ = 0; // pull DQ low to start timeslot
	if(bitval==1) DQ =1; // return DQ high if write 1
	delay(5); // hold value for remainder of timeslot
	DQ = 1;
}// Delay provides 16us per loop, plus 24us. Therefore delay(5) = 104us

//////////////////////////////////////////////////////////////////////////////
// READ_BYTE - reads a byte from the one-wire bus.
//
unsigned char read_byte(void)
{
	unsigned char i;
	unsigned char value = 0;
	for (i=0;i<8;i++)
	{
		if(read_bit()) value|=0x01<<i; // reads byte in, one byte at a time and then
		// shifts it left
		delay(6); // wait for rest of timeslot
	}
	return(value);
}

//////////////////////////////////////////////////////////////////////////////
// WRITE_BYTE - writes a byte to the one-wire bus.
//
void write_byte(char val)
{
	unsigned char i;
	unsigned char temp;
	for (i=0; i<8; i++) // writes byte, one bit at a time
	{
		temp = val>>i; // shifts val right 'i' spaces
		temp &= 0x01; // copy that bit to temp
		write_bit(temp); // write bit in temp into
	}
	delay(5);
}


float Read_Temperature(void)
{
	int idata get[10];
	unsigned char temp_lsb,temp_msb;
	int idata k,temprature_value;
	ow_reset();
	write_byte(0xCC); //Skip ROM
	write_byte(0x44); // Start Conversion
	delay(5);
	ow_reset();
	write_byte(0xCC); // Skip ROM
	write_byte(0xBE); // Read Scratch Pad
	for (k=0;k<9;k++)
	{
		get[k]=read_byte();
	}
	temp_msb =get[1]; // Sign byte + lsbit	
	temp_lsb =get[0]; // Temp data plus lsb	
	if (temp_msb < 0x80)
	{
		temprature_value=(float)(256*temp_msb+temp_lsb)/16;
	}
	else 
	{
		temp_msb=temp_msb&0x7;
		temprature_value=(float)((~(256*temp_msb+temp_lsb)+1)&0x7FF)*(-1)/16;
	}
	return temprature_value;
}
/////////////////////////////////////////////////////////////////////////////////////

UartSend(char * CmdTmp)
{
	char i;
	for(i=0;i<strlen(CmdTmp);i++)
	{
		SBUF=CmdTmp[i];          //发送数据
		while(TI==0);            //发送数据完毕时，TI会自动置高
		TI=0;                    //发送数据完毕，将TI清零，准备下一次发送
	}
}

void uart_Init()
{
	PCON= PCON & 0X7F;			//SMOD=0;选择波特率为普通模式
	TR1=0;						//关闭定时器1，然后进行初始化
	TMOD=TMOD | 0x20;           //定时器1为自动装入方式 模式2、自动再装入8位计数器
   	ET1 = 0;					//禁止T1中断
	SCON=0x40;                  //串行口工作方式1：10位异步收发
	TH1=0xFD;       
	TL1=0xFD;         
	//设置数据格式
	//低位在前
	RI=0;						//清串口接收中断标志
	TI=0;						//清串口发送中断标志
	ES=0;						//禁止串口中断
	TR1=1;						//启动定时器1工作
}

void main(void)
{
	char idata SendBuffer[50]="";
	float tmpdata;
	uart_Init();
	while (1)
	{
		tmpdata=Read_Temperature();
		sprintf(SendBuffer, "%f", tmpdata );
		UartSend("Test DS18B20 : Uart will ouput the temprature if it is right!\r\n");
		UartSend(SendBuffer);
		UartSend("\r\n");
		delay(65535);
		delay(65535);
	}
}