mainenant ça fonctionne, le LM92 n'avait pas le temps pour convertir, il fallait mettre au min 1 sec. (dans le while(true)).
Mainenant je vais faire avec les variables signées,

Code:
#define ADDRESS_LM92_READ              0x91     // lm92 addresse de lecture 
#define ADDRESS_LM92_WRITE             0x90     // lm92 addresse d'écriture
#define SET_POINTER_REGISTER_TEMP      0x00     // adresse du pointeur register Temperature (Read only)
#define SET_POINTER_REGISTER_CONFIG    0x01     // adresse du pointeur register Configuration(Read/Write)
#define CONFIGURATION_STD              0x00     // configuration
#define lm92_manufacturer_id           0x07     // ID manufacturer
//---------------------------------------------------------------------
//                           Variable Globale                        
//---------------------------------------------------------------------
int temp_msb , temp_lsb;
int Manufacturer_ID_msb, Manufacturer_ID_lsb;
//int LM92_temp_data;

//---------------------------------------------------------------------
//                           Fonctions                       
//---------------------------------------------------------------------

// Fonction configuration
void write_in_configuration_register(int config)
{        
    i2c_start();                                // start
    i2c_write(ADDRESS_LM92_WRITE);              // adresse du LM92 en écriture
    i2c_write(SET_POINTER_REGISTER_CONFIG);     // pointeur register Configuration(Read/Write)
    i2c_write(config);                          // configuration 
    i2c_stop();                                 // stop  
}

//------------------------------------------------------------------------------
// Fonction lire température
void read_temp()  
{       
    i2c_start();
    i2c_write(ADDRESS_LM92_WRITE );       // adresse du LM92 en écriture
    i2c_write(SET_POINTER_REGISTER_TEMP); //  pointeur register Temperature (Read only)       
    i2c_start();                          // repeat-start
    i2c_write(ADDRESS_LM92_READ);         // adresse du LM92 en lecture  
    temp_msb = i2c_read(1);               // stockage du msb temperature +ACK  
    temp_lsb = i2c_read(0);               // stockage du Lsb sans ACK  
    i2c_stop();                           // stop
}
void lm92_read_manufacturer_ID()  
{
    i2c_start(); 
    i2c_write(ADDRESS_LM92_WRITE); 
    i2c_write(lm92_manufacturer_id); 
    i2c_start(); 
    i2c_write(ADDRESS_LM92_READ); 
    Manufacturer_ID_msb = i2c_read(1); // ack 
    Manufacturer_ID_lsb = i2c_read(0); // no ack 
    i2c_stop(); 
} 

//---------------------------------------------------------------------
//                           Programme principal                     
//---------------------------------------------------------------------

void main()
{
   setup_comparator(NC_NC_NC_NC);// This device COMP currently not supported by the PICWizard
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_128|RTCC_8_bit);      //32.7 ms overflow
   setup_comparator(NC_NC_NC_NC);// This device COMP currently not supported by the PICWizard
   
   //Internal Oscillator Frequency Select bit 6-4 -> 111 => 8MHz
   bit_set(OSCCON,4);
   bit_set(OSCCON,5);
   bit_set(OSCCON,6);

   delay_ms(100);

   write_in_configuration_register(CONFIGURATION_STD);  //appel à la fonction en fonction de CONFIGURATION_STD

   while(TRUE)
   {  
      read_temp();
      delay_ms(1200);     
   } 
}