// Global variables
int8 RomBytes[8];     
int8 lastDiscrep = 0;
short doneFlag = 0;
int8 FoundROM[9][8];    // Table of found ROM codes, 8 bytes for each
int8 numROMs;
int8 dowcrc;            // crc is accumulated in this variable


//calc_CRC - INTERNAL FUNCTION
//Purpose:    To calculate an 8-bit CRC based on a polynomial and the series
//            of data bytes
//Note:       Polynomial used x^8 + x^5 + x^4 + 1 = 10001100
//Inputs:     A pointer to an array of the data bytes and an int saying how many
//            bytes there are in the data array
//Outputs:    An int8 which is the calculated CRC
int8 calc_CRC(int8* data, int8 bytes)
{
   #define CRC_POLY      0x8C
   int8 shift_register = 0, i, datab, bits;

   for(i = 0; i < bytes; ++i)
   {
      datab = *(data + i);

      for(bits = 0; bits < 8; ++bits)
      {
         if(bit_test((shift_register ^ datab), 0))
         {
            shift_register = shift_register >> 1;
            shift_register ^= CRC_POLY;
         }
         else
         {
            shift_register = shift_register >> 1;
         }

         datab = datab >> 1;
      }
   }
   return shift_register;
} //calc_CRC


// Returns 0 for one wire device presence, 1 for none
int8 ow_reset(void)
{
   int8 presence;
   
   output_low(DQ);
   delay_us(488);          // Min. 480uS
   output_float(DQ);
   delay_us(72);           // Takes 15 to 60uS for devices to respond
   presence = input(DQ);
   delay_us(424);          // Wait for end of timeslot
   return(presence);
}

//******************************************************************************
// Read bit on one wire bus
int8 read_bit(void)
{
   output_low(DQ);
   delay_us(1);         // Added, 1uS min. Code relied on 8051 being slow.
   output_float(DQ);
   delay_us(12);        // Read within 15uS from start of time slot
   return(input(DQ));   
}   

//******************************************************************************
void write_bit(int8 bitval)
{
   output_low(DQ);

   if(bitval == 1) {
      delay_us(1);      // 1uS min. Code relied on 8051 being slow.
      output_float(DQ);
   }
   delay_us(105);       // Wait for end of timeslot
   output_float(DQ);
}

//******************************************************************************
int8 read_byte(void)
{
   int8 i;
   int8 val = 0;

   for(i=0;i<8;i++)
   {
      if(read_bit()) val |= (0x01 << i);
      delay_us(120);  // To finish time slot
   }

   return val;
}

//******************************************************************************
void write_byte(int8 val)
{
   int8 i;
   int8 temp;

   for (i=0;i<8;i++)
   {
      temp = val >> i;
      temp &= 0x01;
      write_bit(temp);
   }

   delay_us(105);
}

//******************************************************************************
// One wire crc
int8 ow_crc(int8 x)
{
   dowcrc = calc_CRC(x,8);
   return dowcrc;
}

//******************************************************************************
// Searches for the next device on the one wire bus. If there are no more
// devices on the bus then false is returned.
int8 Next(void)
{
   int8 m = 1;             // ROM Bit index
   int8 n = 0;             // ROM Byte index
   int8 k = 1;             // Bit mask
   int8 x = 0;
   int8 discrepMarker = 0;
   int8 g;                 // Output bit
   int8 nxt;               // Return value
   short flag;

   nxt = FALSE;            // Reset next flag to false
   dowcrc = 0;             // Reset the dowcrc
   flag = ow_reset();

   if (flag||doneFlag)     // If no parts return false
   {
      lastDiscrep = 0;     // Reset the search
      return FALSE;
   }
   
   write_byte(0xF0);       // Send SearchROM command
   do
   {
      x = 0;
      if (read_bit() == 1)
         x = 2;
      delay_us(120);
      if (read_bit() == 1)
         x |= 1;                    // And it's complement 
      if (x == 3)                   // There are no devices on the one wire bus
         break;
      else
      {
         if (x > 0)                 // All devices coupled have 0 or 1
            g = x >> 1;             // Bit write value for search

         // If this discrepancy is before the last discrepancy on a previous
         // Next then pick the same as last time.
         else
         {
            if (m < lastDiscrep)
               g = ((RomBytes[n] & k) > 0);
            // If equal to last pick 1
            else
               g = (m == lastDiscrep);  // If not then pick 0

               // If 0 was picked then record position with mask k
               if (g == 0) discrepMarker = m;
         }

         // Isolate bit in ROM[n] with mask k
         if (g == 1) RomBytes[n] |= k;
         else RomBytes[n] &= ~k;

         write_bit(g);  // ROM search write

         m++;           // Increment bit counter m
         k = k << 1;    // and shift the bit mask k
         // If the mask is 0 then go to new ROM
         if (k == 0)
         {  // Byte n and reset mask
            ow_crc(RomBytes[n]);      // Accumulate the crc
            n++;
            k++;
         }
      }
   } while (n < 8);  // Loop through until through all ROM bytes 0-7

   if (m < (65||dowcrc))   // If search was unsuccessful then
      lastDiscrep = 0;     // reset the last Discrepancy to zero
   else  // Search was successful, so set lastDiscrep, lastOne, nxt
   {
      lastDiscrep = discrepMarker;
      doneFlag = (lastDiscrep == 0);
      nxt = TRUE; // Indicates search not yet complete, more parts remain
   }

   return nxt;
}

//******************************************************************************
// Resets current state of a ROM search and calls Next to find the first device
// on the one wire bus.
int8 First(void)
{
   lastDiscrep = 0;
   doneFlag = FALSE;
   return Next();    // Call Next and return it's return value;
}

//******************************************************************************
int8 FindDevices(void)
{
   int8 m, cont = 0;
   if(!ow_reset())
   {
      if(First())    // Begins when at least one part found
      {
         numROMs = 0;
         do
         {
            numROMs++; 
            cont++;
            for (m=0;m<8;m++)
            {
               FoundROM[numROMs][m] = RomBytes[m];
            }
         } while (Next());   // Continues until no additional                             
      }
   }
   return cont;

}

//******************************************************************************
// Sends Match ROM command to bus then device address
int8 Send_MatchRom(void)
{
   int8 i;
   if (ow_reset()) return FALSE;          // 0 if device present
   write_byte(0x55);                      // Match ROM

   for (i=0;i<8;i++)
   {
      write_byte(FoundRom[numROMs][i]);   // Send ROM code
   }

   return TRUE;
}