STM32学习笔记之 DS18B20 SEARCH ROM

                // serial number search direction write bit
                OWWriteBit(search_direction);

                // increment the byte counter id_bit_number
                // and shift the mask rom_byte_mask
                id_bit_number++;
                rom_byte_mask <<= 1;

                // if the mask is 0 then go to new SerialNum byte rom_byte_number and reset mask
                if (rom_byte_mask == 0)
                {
                    docrc8(ROM_NO[rom_byte_number]);  // accumulate the CRC
                    rom_byte_number++;
                    rom_byte_mask = 1;
                }
            }
        }
        while(rom_byte_number < 8);  // loop until through all ROM bytes 0-7

        // if the search was successful then
        if (!((id_bit_number < 65) || (crc8 != 0)))
        {
            // search successful so set LastDiscrepancy,LastDeviceFlag,search_result
            LastDiscrepancy = last_zero;

            // check for last device
            if (LastDiscrepancy == 0)
                LastDeviceFlag = TRUE;

            search_result = TRUE;
        }       
    }

    // if no device found then reset counters so next 'search' will be like a first
    if (!search_result || !ROM_NO[0])
    {
        LastDiscrepancy = 0;
        LastDeviceFlag = FALSE;
        LastFamilyDiscrepancy = 0;
        search_result = FALSE;
    }

    return search_result;
}

//--------------------------------------------------------------------------
// Verify the device with the ROM number in ROM_NO buffer is present.
// Return TRUE  : device verified present
//        FALSE : device not present
//
int OWVerify()
{
    unsigned char rom_backup[8];
    int i,rslt,ld_backup,ldf_backup,lfd_backup;

    // keep a backup copy of the current state
    for (i = 0; i < 8; i++)
        rom_backup[i] = ROM_NO[i];
    ld_backup = LastDiscrepancy;
    ldf_backup = LastDeviceFlag;
    lfd_backup = LastFamilyDiscrepancy;

    // set search to find the same device
    LastDiscrepancy = 64;
    LastDeviceFlag = FALSE;

    if (OWSearch())
    {
        // check if same device found
        rslt = TRUE;
        for (i = 0; i < 8; i++)
        {
            if (rom_backup[i] != ROM_NO[i])
            {
                rslt = FALSE;
                break;
            }
        }
    }
    else
        rslt = FALSE;

    // restore the search state
    for (i = 0; i < 8; i++)
        ROM_NO[i] = rom_backup[i];
    LastDiscrepancy = ld_backup;
    LastDeviceFlag = ldf_backup;
    LastFamilyDiscrepancy = lfd_backup;

    // return the result of the verify
    return rslt;
}

//--------------------------------------------------------------------------
// Setup the search to find the device type 'family_code' on the next call
// to OWNext() if it is present.
//
void OWTargetSetup(unsigned char family_code)
{
    int i;

    // set the search state to find SearchFamily type devices
    ROM_NO[0] = family_code;
    for (i = 1; i < 8; i++)
        ROM_NO[i] = 0;
    LastDiscrepancy = 64;
    LastFamilyDiscrepancy = 0;
    LastDeviceFlag = FALSE;
}

//--------------------------------------------------------------------------
// Setup the search to skip the current device type on the next call
// to OWNext().
//
void OWFamilySkipSetup()
{
    // set the Last discrepancy to last family discrepancy
    LastDiscrepancy = LastFamilyDiscrepancy;
    LastFamilyDiscrepancy = 0;

    // check for end of list
    if (LastDiscrepancy == 0)
        LastDeviceFlag = TRUE;
}

//--------------------------------------------------------------------------
// 1-Wire Functions to be implemented for a particular platform
//--------------------------------------------------------------------------

//--------------------------------------------------------------------------
// Reset the 1-Wire bus and return the presence of any device
// Return TRUE  : device present
//        FALSE : no device present
//
int OWReset()
{
    u8 temp = 0;
    DQ(1);
    DQ(0);
    DqDelay(784);                    //784
    DQ(1);
    DqDelay(110);                    //110
    temp = READ_DQ;
    DqDelay(675);                      //675

    return !temp;    
}

//--------------------------------------------------------------------------
// Send 8 bits of data to the 1-Wire bus
//
void OWWriteByte(unsigned char dat)
{
    u8 i = 0;
    for ( i = 0 ; i < 8 ; i++ )
    {
        DQ(0);
        DqDelay(1);
        if ( dat & 0x01 )
        {
            DQ(1);   
        }
        else
        {
            DQ(0);
        }
        dat = dat >> 1;
        DqDelay(100);
        DQ(1);
        DqDelay(1);           
    }

}

//--------------------------------------------------------------------------
// Send 1 bit of data to teh 1-Wire bus
//
void OWWriteBit(unsigned char bit_value)
{
    DQ(0);
    DqDelay(1);
    if ( bit_value & 0x01 )
    {
        DQ(1);   
    }
    else
    {
        DQ(0);
    }
    DqDelay(100);
    DQ(1);
    DqDelay(1);       
}

//--------------------------------------------------------------------------
// Read 1 bit of data from the 1-Wire bus
// Return 1 : bit read is 1
//        0 : bit read is 0
//
unsigned char OWReadBit()
{
    u8 dat = 0;
    DQ(0);
    DqDelay(1);
    DQ(1);
    DqDelay(2);
    if ( READ_DQ )
    {
        dat = 1;
    }
    DqDelay(100);
    return dat;
}

// TEST BUILD
static unsigned char dscrc_table[] = {
    0, 94,188,226, 97, 63,221,131,194,156,126, 32,163,253, 31, 65,
    157,195, 33,127,252,162, 64, 30, 95,  1,227,189, 62, 96,130,220,
    35,125,159,193, 66, 28,254,160,225,191, 93,  3,128,222, 60, 98,
    190,224,  2, 92,223,129, 99, 61,124, 34,192,158, 29, 67,161,255,
    70, 24,250,164, 39,121,155,197,132,218, 56,102,229,187, 89,  7,
    219,133,103, 57,186,228,  6, 88, 25, 71,165,251,120, 38,196,154,
    101, 59,217,135,  4, 90,184,230,167,249, 27, 69,198,152,122, 36,
    248,166, 68, 26,153,199, 37,123, 58,100,134,216, 91,  5,231,185,
    140,210, 48,110,237,179, 81, 15, 78, 16,242,172, 47,113,147,205,
    17, 79,173,243,112, 46,204,146,211,141,111, 49,178,236, 14, 80,
    175,241, 19, 77,206,144,114, 44,109, 51,209,143, 12, 82,176,238,
    50,108,142,208, 83, 13,239,177,240,174, 76, 18,145,207, 45,115,
    202,148,118, 40,171,245, 23, 73,  8, 86,180,234,105, 55,213,139,
    87,  9,235,181, 54,104,138,212,149,203, 41,119,244,170, 72, 22,
    233,183, 85, 11,136,214, 52,106, 43,117,151,201, 74, 20,246,168,
    116, 42,200,150, 21, 75,169,247,182,232, 10, 84,215,137,107, 53};