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下面给出了搜索算法的‘C’程序代码及实现每个变量搜索算法的函数。FamilySkipSetup和TargetSetup函数实际上并没有进行搜索操作，它们只不过是用来设置搜索寄存器，以便在下一次执行‘NEXT’操作时能跳过或找到所期望的类型。需要注意的是低级1-Wire函数可通过调用TMEX API实现。这些程序调用只是用于系统测试，也可以用特定平台调用。关于TMEX API和其它一些1-Wire API的详细资料请参考应用笔记155。

下列TMEX API测试程序的源代码可从Maxim网页下载。

// TMEX API TEST BUILD DECLARATIONS
#define TMEXUTIL
#include "ibtmexcw.h"
long session_handle;
// END TMEX API TEST BUILD DECLARATIONS

// definitions
#define FALSE 0
#define TRUE  1

// method declarations
int  OWFirst();
int  OWNext();
int  OWVerify();
void OWTargetSetup(unsigned char family_code);
void OWFamilySkipSetup();
int  OWReset();
void OWWriteByte(unsigned char byte_value);
void OWWriteBit(unsigned char bit_value);
unsigned char OWReadBit();
int  OWSearch();
unsigned char docrc8(unsigned char value);

// global search state
unsigned char ROM_NO[8];
int LastDiscrepancy;
int LastFamilyDiscrepancy;
int LastDeviceFlag;
unsigned char crc8;

//--------------------------------------------------------------------------
// Find the 'first' devices on the 1-Wire bus
// Return TRUE  : device found, ROM number in ROM_NO buffer
//        FALSE : no device present
//
int OWFirst()
{
   // reset the search state
   LastDiscrepancy = 0;
   LastDeviceFlag = FALSE;
   LastFamilyDiscrepancy = 0;

   return OWSearch();
}

//--------------------------------------------------------------------------
// Find the 'next' devices on the 1-Wire bus
// Return TRUE  : device found, ROM number in ROM_NO buffer
//        FALSE : device not found, end of search
//
int OWNext()
{
   // leave the search state alone
   return OWSearch();
}

//--------------------------------------------------------------------------
// Perform the 1-Wire Search Algorithm on the 1-Wire bus using the existing
// search state.
// Return TRUE  : device found, ROM number in ROM_NO buffer
//        FALSE : device not found, end of search
//
int OWSearch()
{
   int id_bit_number;
   int last_zero, rom_byte_number, search_result;
   int id_bit, cmp_id_bit;
   unsigned char rom_byte_mask, search_direction;

   // initialize for search
   id_bit_number = 1;
   last_zero = 0;
   rom_byte_number = 0;
   rom_byte_mask = 1;
   search_result = 0;
   crc8 = 0;

   // if the last call was not the last one
   if (!LastDeviceFlag)
   {
      // 1-Wire reset
      if (!OWReset())
      {
         // reset the search
         LastDiscrepancy = 0;
         LastDeviceFlag = FALSE;
         LastFamilyDiscrepancy = 0;
         return FALSE;
      }

      // issue the search command 
      OWWriteByte(0xF0);  

      // loop to do the search
      do
      {
         // read a bit and its complement
         id_bit = OWReadBit();
         cmp_id_bit = OWReadBit();

         // 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
            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()
{
   // platform specific
   // TMEX API TEST BUILD
   return (TMTouchReset(session_handle) == 1);
}

//--------------------------------------------------------------------------
// Send 8 bits of data to the 1-Wire bus
//
void OWWriteByte(unsigned char byte_value)
{
   // platform specific
   
   // TMEX API TEST BUILD
   TMTouchByte(session_handle,byte_value);
}

//--------------------------------------------------------------------------
// Send 1 bit of data to teh 1-Wire bus
//
void OWWriteBit(unsigned char bit_value)
{
   // platform specific

   // TMEX API TEST BUILD
   TMTouchBit(session_handle,(short)bit_value);
}

//--------------------------------------------------------------------------
// Read 1 bit of data from the 1-Wire bus 
// Return 1 : bit read is 1
//        0 : bit read is 0
//
unsigned char OWReadBit()
{
   // platform specific

   // TMEX API TEST BUILD
   return (unsigned char)TMTouchBit(session_handle,0x01);

}

// 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};

//--------------------------------------------------------------------------
// Calculate the CRC8 of the byte value provided with the current 
// global 'crc8' value. 
// Returns current global crc8 value
//
unsigned char docrc8(unsigned char value)
{
   // See Application Note 27
   
   // TEST BUILD
   crc8 = dscrc_table[crc8 ^ value];
   return crc8;
}

//--------------------------------------------------------------------------
// TEST BUILD MAIN
//
int main(short argc, char **argv)
{
   short PortType=5,PortNum=1;
   int rslt,i,cnt;

   // TMEX API SETUP
   // get a session
   session_handle = TMExtendedStartSession(PortNum,PortType,NULL);
   if (session_handle <= 0)
   {
      printf("No session, %d\n",session_handle);
      exit(0);
   }

   // setup the port
   rslt = TMSetup(session_handle);
   if (rslt != 1)
   {
      printf("Fail setup, %d\n",rslt);
      exit(0);
   }
   // END TMEX API SETUP

   // find ALL devices
   printf("\nFIND ALL\n");
   cnt = 0;
   rslt = OWFirst();
   while (rslt)
   {
      // print device found
      for (i = 7; i >= 0; i--)
         printf("%02X", ROM_NO[i]);
      printf("  %d\n",++cnt);

      rslt = OWNext();
   }

   // find only 0x1A
   printf("\nFIND ONLY 0x1A\n");
   cnt = 0;
   OWTargetSetup(0x1A);
   while (OWNext())
   {
      // check for incorrect type
      if (ROM_NO[0] != 0x1A)
         break;
      
      // print device found
      for (i = 7; i >= 0; i--)
         printf("%02X", ROM_NO[i]);
      printf("  %d\n",++cnt);
   }

   // find all but 0x04, 0x1A, 0x23, and 0x01
   printf("\nFIND ALL EXCEPT 0x10, 0x04, 0x0A, 0x1A, 0x23, 0x01\n");
   cnt = 0;
   rslt = OWFirst();
   while (rslt)
   {
      // check for incorrect type
      if ((ROM_NO[0] == 0x04) || (ROM_NO[0] == 0x1A) || 
          (ROM_NO[0] == 0x01) || (ROM_NO[0] == 0x23) ||
          (ROM_NO[0] == 0x0A) || (ROM_NO[0] == 0x10))
          OWFamilySkipSetup();
      else
      {
         // print device found
         for (i = 7; i >= 0; i--)
            printf("%02X", ROM_NO[i]);
         printf("  %d\n",++cnt);
      }

      rslt = OWNext();
   }

   // TMEX API CLEANUP
   // release the session
   TMEndSession(session_handle);
   // END TMEX API CLEANUP
}

修订历史
01/30/02版1.0—初始版本。
05/16/03版1.1—修改内容：Search ROM命令修改为F0 (十六进制)。