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Emulating a DS2401 on 16F88

 
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dorinm



Joined: 07 Jan 2006
Posts: 38

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Emulating a DS2401 on 16F88
PostPosted: Mon Feb 21, 2011 7:36 am     Reply with quote

this is the whole code needed to emulate a DS2401 8byte serial number;
it is based on some code found on web written for hitech compiler (as far as I remember), the code didn't mention the author so I can't do that either;
...the original code has some bugs in it (mainly bad timming and "corner-cuts"; also the reset procedure in the interrupt routine was not ok), I have just adapted it for CCS and corrected where it was necessary;
... I do not take any responsability on how it's used

Code:

#include <16f88.h>
#device *=16

#fuses HS, WDT, PUT, MCLR, NOPROTECT, NOBROWNOUT, NOLVP, NOCPD, NOWRT, NODEBUG, NOPROTECT, NOIESO, NOFCMEN

//i've tried also with lower frequencies, there are problems with precise timmings
//so I recomend using 20MHZ; do not even think about internal RC ;)
#use delay(clock=20000000)
#use fast_io(B)

//some arbitrary serial data
#rom 0x2100={0x01,0x11,0x22,0x33,0x44,0x55,0x69,0x00}

// comment it out if you're not using leds for debugging
#define  MOD_TEST

#define  LED_PWR   PIN_B1
#define  LED_RST   PIN_B2
#define  LED_RX    PIN_B3
#define  LED_TX    PIN_B4

//the pin used for interfacing with DS2401
//do not forget that sometimes you should use a pullup resistor on this line, 50k>(100k) should be fine
//be aware about the fact that in some cicumstances the DS's are powered up using parasite mode (by DQ line),
//this is not the case so you should power up your schematics from your 5V line
#define  DS_DQ       PIN_B0

#define  PLIN        1
#define  GOL         0
#define  BUFFER_MAX  7

#define  INIT_SEQ    (flag_Rx=FALSE, flag_BUF_Rx=GOL, bit_curent=0)


int1  flag_Rx;
int1  flag_BUF_Rx;

int8  BUF_Rx;
int1  bRx;
int8  BUF_Tx[8];
int8  SN[8];

int8  bit_curent, buffer_index, del_count;






#INT_EXT
void interrupt(void)
{
 
   if (flag_Rx)
   {
   
       #ifdef MOD_TEST
       output_high(LED_RX);
       #endif
     
      delay_us(15);
      bRx = input(DS_DQ);
      flag_BUF_Rx = GOL;
      bit_curent++;
     
      if (bit_curent == 8)
      {
               #ifdef MOD_TEST
               output_low(LED_RX);
               #endif

         flag_BUF_Rx = PLIN;
         bit_curent = 0;

      }
     
      BUF_Rx >>= 1;
      if (bRx)
         BUF_Rx |= 0x80;
      delay_us(5);


      if(input(DS_DQ))
      {
               #ifdef MOD_TEST
               output_low(LED_RX);
               #endif
         clear_interrupt(INT_EXT);
         return;
      }
     
      else
      {
         del_count = 45;
         while (del_count--)
         {
         if (input(DS_DQ))
            {
               #ifdef MOD_TEST
               output_low(LED_RX);
               #endif
               clear_interrupt(INT_EXT);
               return;
            }
         }
      }
   }





   RST:

      set_tris_b(0b00000001);

      #ifdef MOD_TEST
      output_high(LED_RST);
      #endif
     
      delay_us(200);
   
      while(!input(DS_DQ));
         
      delay_us(30);
      output_low(DS_DQ);
      set_tris_b(0b00000000);
      delay_us(480);
     
      INIT_SEQ;
      flag_Rx = TRUE;
      set_tris_b(0b00000001);

   
      #ifdef MOD_TEST
      output_low(LED_RST);
      #endif
   
      clear_interrupt(INT_EXT);
      return;
     
   
}


void C_CRC(byte *CRCVal, int8 value)
{
     int8 odd, bcnt;

     for (bcnt=0; bcnt<8; bcnt++)
   {
      odd = (value ^ *CRCVal) & 0x01;
       *CRCVal >>= 1;
       value >>= 1;
       if (odd != 0)
         *CRCVal ^= 0x8C;
     }
}


int8 CalcCRC(byte code_len, int8 *code)
{
   int8 i, CRCVal=0;

     for ( i=0; i<code_len; i++ )
       C_CRC( &CRCVal, code[i] );

     return CRCVal;
}


void Read_SN(void)
{
   int8 adresa;

   for ( adresa=0; adresa<BUFFER_MAX; adresa++ )
      SN[adresa] = read_eeprom (adresa);

   
   SN[adresa] = CalcCRC(7, SN);
}




/******************* MAIN *****************/

void main() {

   int8 i,mask;


   setup_wdt(WDT_2304MS);
 
   INIT_SEQ;

   Read_SN();
   
   BUF_Rx = 0;

   setup_adc(ADC_OFF);
   setup_adc_ports(NO_ANALOGS);
   set_tris_a(0b11111111);
   set_tris_b(0b00000001);
   output_float(DS_DQ);
   ext_int_edge( H_TO_L );
   enable_interrupts(INT_EXT);
   enable_interrupts(GLOBAL);

   #ifdef MOD_TEST
   output_high(LED_PWR);
   #endif


  for(i=0; i<8; i++)
  BUF_Tx[i] = SN[i];


   while(TRUE)
   {
         
      if (flag_BUF_Rx == PLIN)
      {

            if (BUF_Rx == 0x33)
            {
               #ifdef MOD_TEST
               output_high(LED_TX);
               #endif
           

               disable_interrupts(INT_EXT);
               set_tris_b(0b00000001);
               
               for (buffer_index=0; buffer_index<8; buffer_index++)
               {
                  for (bit_curent=0; bit_curent<8; bit_curent++)
                  {
                     set_tris_b(0b00000001);
                     while(input(DS_DQ));
                     output_low(DS_DQ);
                     mask=0x01 & BUF_Tx[buffer_index];
                     set_tris_b(mask);
                     
                    delay_us(35);
                    set_tris_b(0b00000001);
                       
                    BUF_Tx[buffer_index] >>= 1;
                     
                  }
               }                   
     
             
               #ifdef MOD_TEST
               output_low(LED_TX);
               #endif
                   
               for(i=0; i<8; i++)
               BUF_Tx[i] = SN[i];
               INIT_SEQ;
               restart_wdt();
               clear_interrupt(INT_EXT);
               enable_interrupts(INT_EXT);
            }
         restart_wdt();
      }
   }
}


feel free to ask questions if you need

Dorin M
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