//从DS18B20读取一个字节
//返回值：读到的数据
u8 DS18B20_Read_Byte(void) // read one byte
{
u8 i,j,dat;
dat=0;
for (i=1;i<=8;i++)
{
j=DS18B20_Read_Bit();
dat=(j<<7)|(dat>>1);
}
return dat;
}
//从DS18B20读取一个字节
//返回值：读到的数据
u8 DS18B20_Read_Byte(void) // read one byte
{
u8 i,j,dat;
dat=0;
for(i=0; i<8; i++)
{
j = DS18B20_Read_Bit();
dat = (dat) | (j<<i);
}
return dat;
}
u8 OWSearch(u8 *newAddr)
{
u8 id_bit_number;
u8 last_zero, rom_byte_number, search_result;
u8 id_bit, cmp_id_bit;
int i;
unsigned char rom_byte_mask, search_direction;
static unsigned char ROM_NO[8];
static u32 LastDiscrepancy = 0;
static u8 LastDeviceFlag = FALSE;
static u32 LastFamilyDiscrepancy = 0;
// initialize for search
id_bit_number = 1;
last_zero = 0;
rom_byte_number = 0;
rom_byte_mask = 1;
search_result = 0;
// if the last call was not the last one
if (!LastDeviceFlag)
{
// 1-Wire reset
DS18B20_Rst();
if(DS18B20_Check())
{
// reset the search
LastDiscrepancy = 0;
LastDeviceFlag = FALSE;
LastFamilyDiscrepancy = 0;
return FALSE;
}
// issue the search command
DS18B20_Write_Byte(0xF0);
// loop to do the search
do
{
// read a bit and its complement
id_bit = DS18B20_Read_Bit();
cmp_id_bit = DS18B20_Read_Bit();
// check for no devices on 1-wire
if ((id_bit == 1) && (cmp_id_bit == 1))
break;
else
{
// all devices coupled have 0 or 1
if (id_bit != cmp_id_bit)
search_direction = id_bit; // bit write value for search
else
{
// if this discrepancy if before the Last Discrepancy
// on a previous next then pick the same as last time
if (id_bit_number < LastDiscrepancy)
search_direction = ((ROM_NO[rom_byte_number] & rom_byte_mask) > 0);
else
// if equal to last pick 1, if not then pick 0
search_direction = (id_bit_number == LastDiscrepancy);
// if 0 was picked then record its position in LastZero
if (search_direction == 0)
{
last_zero = id_bit_number;
// check for Last discrepancy in family
if (last_zero < 9)
LastFamilyDiscrepancy = last_zero;
}
}
// set or clear the bit in the ROM byte rom_byte_number
// with mask rom_byte_mask
if (search_direction == 1)
ROM_NO[rom_byte_number] |= rom_byte_mask;
else
ROM_NO[rom_byte_number] &= ~rom_byte_mask;
// serial number search direction write bit
OWWrite_bit(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)
{
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))
{
// 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;
}
for (i = 0; i < 8; i++) newAddr[i] = ROM_NO[i];
return search_result;
}
