要关中断,
在每个字节读写时序发起时的低电平时关中断,时间只有几个US,
不是在整个读写数据期间关中断
以下是一个PIC16F877的用18B20测温的部分程序
#include <pic.h>
#include "temperature.h"
#include "main.h"
bank1 bit RE2Bit;
bank1 bit bStartConversion;
bank1 unsigned int TemperatureMs1000;
bank1 bit bWaitConversion;
bank1 bit bCanRead;
bank1 bit tempBit;
void InitTemperatureTest()
{
TRISE2 = 1;
bStartConversion = 1;
TemperatureMs1000 = 1000;
bWaitConversion = 0;
bCanRead = 0;
// Not set 18B20,12 bit precision
}
bit Reset18B20()
{
RE2 = 0;
TRISE2 = 0;
SetDelayTenUs(55);//3+500 US
TRISE2 = 1;//Set Input,RES pull High
SetDelayTenUs(7);//73 us
tempBit = RE2;
SetDelayTenUs(24);//240us
return tempBit;
}
unsigned char ReadOneChar()
{
unsigned char i=0;
unsigned char dat = 0;
for (i=8;i>0;i--)
{
GIE = 0;//Close Globle Intterupt
RE2 = 0;//delay 2us
TRISE2 = 0;
dat>>=1;
asm("NOP");
TRISE2 = 1;
//delay 4Us
asm("NOP");
asm("NOP");
asm("NOP");
asm("NOP");
RE2Bit = RE2;
GIE = 1;//Open Globle Intterupt
if(RE2Bit)
{
dat |= 0x80;
}
SetDelayTenUs(5);//53 us,all > 60Us
}
return(dat);
}
void WriteOneChar(unsigned char dat)
{
unsigned char j;
for(j=8; j>0; j--)
{
GIE = 0;//Close Globle Intterupt
RE2 = 0;//delay 2us
TRISE2 = 0;
asm("NOP");
asm("NOP");
RE2 = dat&0x01;
GIE = 1;//Open Globle Intterupt
SetDelayTenUs(6);//63us
TRISE2 = 1;
dat>>=1;
}
SetDelayTenUs(10);//103us
}
bit StartTemperatureTest()
{
if(!Reset18B20())
{
WriteOneChar(0xCC); // ignore ROM Oprator
WriteOneChar(0x44); // start temperature conversion
bStartConversion = 0;
TemperatureMs1000 = 1000;
bWaitConversion = 1;
return 1;
}
return 0;
}
unsigned char ReadTemperature()
{
unsigned char a=0;
unsigned char b=0;
unsigned char t=0;
if(!Reset18B20())
{
WriteOneChar(0xCC); // ignore ROM Oprator
WriteOneChar(0xBE); //read cmd
a=ReadOneChar(); //low char
b=ReadOneChar(); //high char
a=a>>4; //低位右移4位，舍弃小数部分
t=b<<4; //高位左移4位，舍弃符号位
t |= a;
t |= (b & 0x80);
bCanRead = 0;
bStartConversion = 1;
}
return(t);
}
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