romserch.c

该代码实现了单总线器件 在线动态识别的功能

#include "DS18B20.h"

//Rev CRC8 register
//需要在使用前由调用它的程序将其清零
unsigned char   revCRC8;

//temp memory of 18B20 ROM data, using for search command
//the last two byte contains the search infomation
unsigned char   B20ROMTemp[9];
#define         LastUnknow   B20ROMTemp[8]
unsigned char   DetectB20()
{
    unsigned char i=ReDetectTime;
    do{
        PullDownDQ();   //Pull DQ to Low votage
        Delay480us();   //Delay 480us
        ReleaseDQ();    //Release DQ to High
        Delay60us();    //Delay 60us
        if(!B20DQ)      //is DQ is Low, Detect Success, return 1
        {    Delay480us();
             return  1;
        }
        Delay480us();
    }while(--i);
    //Detect over time
    return  0;
}

void    WriteB20Byte(unsigned char tmp)
{
    unsigned char i=8;
    do{
        // the LSB tmp bit will write to 18B20
        WriteB20Bit(&tmp);
        tmp>>=1;
    }while(--i);
}
unsigned char ReadB20Byte()
{
    unsigned char tmp;
    unsigned char i=8;
    do{
        tmp>>=1;
        //The bit value will write to LSB of tmp
        ReadB20Bit(&tmp);
    }while(--i);
    return tmp;
}

unsigned char   ReadB20ROM(unsigned char *ROM)
{
       unsigned char i=8;
       revCRC8=0;
       if(DetectB20())
       {
       WriteB20Byte(ReadROM);
       do{
            *ROM=ReadB20Byte();
            ROM++;
       }while(--i);
       if(revCRC8)
            return CRCError;
       return  0;
       }
       return  OverTime;
}

unsigned char   ReadEERAM(unsigned char *RAM)
{
       unsigned char i=9;
       revCRC8=0;
       if(DetectB20())
       {
       WriteB20Byte(SkipROM);
       WriteB20Byte(B20ReadScr);
       do{
            *RAM=ReadB20Byte();
            RAM++;
       }while(--i);
       if(revCRC8)
            return CRCError;
       return  0;
       }
       return  OverTime;
}

void    Delay10us(unsigned char tmp)
{
    unsigned char i;
    do{
        for(i=5;--i;);
    }while(--tmp);
}
unsigned char   SearchDevice(unsigned char FirstNext)
{   //*
    unsigned char i,tmp;
    unsigned char *j=B20ROMTemp;
    unsigned char ROMOut;  //will read out ROM
    unsigned char ThisUnknow = 0xFF;
    if(FirstNext==FindFirst)
    {
        for(;j<(B20ROMTemp+8);j++)
            *j=0;
        j=B20ROMTemp;
        LastUnknow=ThisUnknow;
    }
    if(!DetectB20())
        return OverTime;
    WriteB20Byte(SearchROM);
    for(i=0;!(i&64);)
    {
        if(!(i&0x07))        // Load old ROM infomation
            ROMOut=*j;
        tmp=0;
        ReadB20Bit(&tmp);
        tmp>>=1;
        ReadB20Bit(&tmp);
        // I'll judge the device by highest two bits of tmp
        // 00 there has multiple device
        // 01 the first bit is 1
        // 10 the first bit is 0
        // 11 there has no device
        if(tmp&0x40){ // if the sytle is 1x
            if(tmp&0x80) // 11
                return OverTime; //no device so return directly
            tmp|=1;        // 10 this bit is 1 so write 1 to device
        }
        else{         // sytle is 0x
            if(!(tmp&0x80)){      //00 there has multiple device
                //there has two choice there
                //if the bit here set last time is 1
                //this is a normal bit, do as read 10
                if( (ROMOut&0x01) || (LastUnknow==i) )
                    tmp|=1;
                else   // if it not the LastUnknoe bit
                   //set it to thisunknow bit
                    //and set it to 0 , write it to 0
                    ThisUnknow=i;
            }
        }
        WriteB20Bit(&tmp);
        ROMOut>>=1;
        if(tmp&0x01)
            ROMOut|=0x80;
        if(!((++i)&0x07)) 
           *j++=ROMOut ;    // Save new ROM infomation
    }
    LastUnknow=ThisUnknow;    //set new unknow bit
    if(ThisUnknow==0xFF)      //if ThisUnknow didn't change, 
        return SearchFinish;  //there is no unknown bit
    return 0;    //if there still have unknow bit, just return 0
}

void    WriteB20Bit(unsigned char *tp)
{
        PullDownDQ();
        NOP();
        if((*tp)&0x01)
        {
            ReleaseDQ();
        }
        Delay60us();
        ReleaseDQ();
}
void    ReadB20Bit(unsigned char *tp)
{
        PullDownDQ();
        NOP();
        NOP();
        ReleaseDQ();
        NOP();
        revCRC8>>=1;
        if(CARRY)
            revCRC8^=v_revCRC8;
        if(B20DQ)
        {
            (*tp)|=0x80;
            revCRC8^=v_revCRC8;
        }
        Delay60us();
}
unsigned char StartConvertTp()
{
    if(DetectB20())
    {
        WriteB20Byte(SkipROM);
        WriteB20Byte(B20Convert);
        return 0;
    }
    return OverTime;
}