ds18b20.c

关于温度传感器和电机测速的单片机程序

#include <intrins.h>
#include <reg51.h>

//这里以11.0592M晶体为例，不同的晶体速度可能需要调整延时的时间
sbit DQ = P3^5;
unsigned char m_CRC(unsigned char CRC0,unsigned char InByt);

//延时
void delay(unsigned int useconds)
{
	for(;useconds>0;useconds--);
}
void delay750()
{
int x;
	for(x=0;x<20000;x++) {}	
	for(x=0;x<20000;x++) {}	
	for(x=0;x<20000;x++) {}	
	for(x=0;x<20000;x++) {}	
	for(x=0;x<20000;x++) {}	
	for(x=0;x<20000;x++) {}	
	for(x=0;x<20000;x++) {}	
	for(x=0;x<20000;x++) {}	
}

//复位
bit ow_reset(void)	// 0=presence, 1 = no part
{
bit presence;
char count;
	DQ = 0; 	//pull DQ line low
	delay(42); 	// leave it low for 480us
	DQ = 1; 	// allow line to return high
	count = 0;
	delay(2);
	do 
	{
		delay(1); 	// the first is for recover period
		presence = DQ;
		count++;
	} while (presence && (count<8));
	if(count>=8) return 1;
	count = 0;
	do
	{
		delay(1);
		presence = DQ;
		count++;
	} while	(!presence&&(count<60));
	if(count>=60) return 1;	// 如果拉死，也认为不存在	
	delay(36);
	return 0;
} 	

//从 1-wire 总线上读取一个字节
unsigned char read_byte(void)
{
unsigned char i;
unsigned char value = 0;
	for (i=8;i>0;i--)
	{
		value>>=1;
		DQ = 0; // pull DQ low to start timeslot
		DQ = 0; // then return high
		DQ = 1; // then return high
		DQ = 1; // then return high
				// 
		_nop_();
		_nop_();
		_nop_();
		_nop_();
		_nop_();
		_nop_();
		_nop_();
		_nop_();
		if(DQ)value|=0x80;
		delay(4); // wait for rest of timeslot
	}
	return(value);
}

//向 1-WIRE 总线上写一个字节
void write_byte(char val)
{
unsigned char i;
	for (i=8; i>0; i--) // writes byte, one bit at a time
	{
		DQ = 0; // pull DQ low to start timeslot
		DQ = 0; //pull DQ line low
		DQ = val&0x01;
		delay(5); // hold value for remainder of timeslot
		DQ = 1;
		val=val/2;
	}
	delay(5);
}

//读取温度
int Read_Temperature(void)
{
unsigned char xl,xh;
unsigned char cfg;
unsigned int x;
unsigned char crc;
	do
	{
	ow_reset();
	write_byte(0xCC); // Skip ROM
	write_byte(0x44); // Start Conversion
	delay(2);
	delay750();
	ow_reset();
	write_byte(0xCC); // Skip ROM
	write_byte(0xBE); // Read Scratch Pad
	xl = read_byte();
	crc = m_CRC(0,xl);
	xh = read_byte();
	crc = m_CRC(crc,xh);
	cfg = read_byte();	// TH 
	crc = m_CRC(crc,cfg);
	cfg = read_byte();	// TL 
	crc = m_CRC(crc,cfg);
	cfg = read_byte();	// config 
	crc = m_CRC(crc,cfg);
	cfg = read_byte();	// Reserve0 
	crc = m_CRC(crc,cfg);
	cfg = read_byte();	// Reserve1 
	crc = m_CRC(crc,cfg);
	cfg = read_byte();	// Reserve2 
	crc = m_CRC(crc,cfg);
	cfg = read_byte();	// CRC read from inside
	} while(cfg!=crc);
//	ow_reset();

	x = xh;
	x = (x<<8)+xl + 3;	// 4 舍 5 入
	x = (x>>3); 
	x = x + (x<<2);
//	x = cfg;
	return x;
}

int Read_ROM(char k)
{
unsigned char x[8]; 
char i;
	ow_reset();
	write_byte(0x33); // Skip ROM
	for(i = 0;i<8;i++) x[i]	= read_byte();
	ow_reset();
	return x[k];
}