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Multiple DS18B20 with parasite power

 
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sebitnt



Joined: 05 Dec 2010
Posts: 5

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Multiple DS18B20 with parasite power
PostPosted: Wed Mar 02, 2011 11:52 am     Reply with quote

Discussion thread here: http://www.ccsinfo.com/forum/viewtopic.php?t=44186

main.c
Code:

#include <16F877A.H>
#fuses XT,NOWDT,NOLVP,PUT,NOPROTECT,NOBROWNOUT,NOWRT
//#use delay(clock = 20000000)
#use delay(clock = 4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#define DQ PIN_E2 // One Wire Bus pin assignment
#include "onewire.c"

void main(void)
{
   int8 i;
   float temperature;
   int8 scratch[9];
   int8 numRom;

   output_float(DQ);       // Set as input. 4k7 pullup on bus.
   FindDevices();         
   
   while(true)
   {
      if (!ow_reset())     // If a device is present
      {
         write_byte(0xCC,0); // Skip Rom command
         write_byte(0x44,1); // Temperature convert command
         //output_float(DQ);
         delay_ms(750);    // Max. conv. time is 750mS for 12 bit
         //output_float(DQ);
         ow_reset();
 
         // Now get the device raw temperature data using Match ROM with the
         // addresses obtained with FindDevices().
         // If the received crc is same as calculated then data is valid.
         // Scale and round to nearest degree C.
         // Scaling is 0.0625 (1/16) deg.C/bit with default 12 bit resolution.
         // Round by adding half denominator for positive temperatures and
         // subtracting half denominator for negative temperatures.
         for (numRom=1;numRom<=numROMs;numRom++)
         {
            if (Send_MatchRom(numRom))
            {
               write_byte(0xBE,0); // Read scratch pad command
               dowcrc = 0;       
               
               // Get the data bytes
               
               for (i=0;i<=7;i++)
               {
                   scratch[i] = read_byte();
                   ow_crc(scratch[i]);     
               }
   
               scratch[8] = read_byte();   // Get crc byte
               ow_reset();
   
               // If calculated crc from incoming bytes equal to crc byte
               // then data is valid.
                                         
               if (scratch[8] == dowcrc)
               {
                  temperature = (float) make16(scratch[1],scratch[0]);
                 
                  if (temperature >= 0)
                     temperature = (temperature + 8)/16;
               
                  else
                     temperature = (temperature - 8)/16;
                     
               printf("Sensor Number: %u", numRom); 
               printf(" %7.4g\r\n", temperature);
               }
               
               else
                  printf("Error in data\r\n");
            }
         }
        printf("\r\n");
      }   
   }
}



onewire.c
Code:
// One Wire bus functions - from Dallas publication AN162
// "Interfacing DS18x20/DS1822 1-wire Temperature Sensor in a Microcontroller
// Environment". Delays calculated from values given for 8051.
// Changed variable name ROM[] to RomBytes[] because ROM is a reserved word
// in version 4 of the CCS compiler.

// Global variables
int8 RomBytes[8];     
int8 lastDiscrep = 0;
short doneFlag = 0;
int8 FoundROM[12][8];    // Table of found ROM codes, 8 bytes for each
int8 numROMs;
int8 dowcrc;            // crc is accumulated in this variable

// crc lookup table
int8 const 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
};

// 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;
}

//-------------------------------------
//new byte writing routine with parasite power option
void write_byte(int8 val, int8 power_on)
{
int i;

for(i=0; i<8; i++)
   {
    output_low(DQ);
    delay_us( 2 ); 
    output_bit(DQ, shift_right(&val,1,0)); 

    delay_us(60);
 
    if((i == 7) && (power_on == 1))
      {
       output_high(DQ);
      }
    else
      {
       output_float(DQ);
       delay_us( 2 ); 
      }
   }

}

//******************************************************************************
// One wire crc
int8 ow_crc(int8 x)
{
   dowcrc = dscrc_table[dowcrc^x];
   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(0xF0,0);       // 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;
}
//******************************************************************************
void FindDevices(void)
{
   int8 m;

   if(!ow_reset())
   {
      if(First())    // Begins when at least one part found
      {
         numROMs = 0;

         do
         {
            numROMs++;

            for (m=0;m<8;m++)
            {
               FoundROM[numROMs][m] = RomBytes[m];
            }

            printf("Device No.%u address ",numROMs);

            printf("%X%X%X%X%X%X%X%X\n\r",
            FoundROM[numROMs][7],FoundROM[numROMs][6],FoundROM[numROMs][5],
            FoundROM[numROMs][4],FoundROM[numROMs][3],FoundROM[numROMs][2],
            FoundROM[numROMs][1],FoundROM[numROMs][0]);

         } while (Next() && (numROMs<10));   // Continues until no additional
                                             // devices found.
      }
   }
printf("\n");
}
//******************************************************************************
// Sends Match ROM command to bus then device address
int8 Send_MatchRom(int8 actNumRom)
{
   int8 i;
   if (ow_reset()) return FALSE;          // 0 if device present
   write_byte(0x55,0);                      // Match ROM

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

   return TRUE;
}
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