Temperatursensor DS18B20

[Tarlar (Gast)]

Hallo Leute,

ich habe folgenden Temperatursensor bei CONRAD gekauft:
http://www.conrad.de/ce/de/product/184037/TEMP-FUeHLER-DS-1820-KABEL-2-M/SHOP_AREA_37353&promotionareaSearchDetail=005

Ich habe mittlerweile Codeteile hier gefunden, die bei mir so im Code 
eingebaut sind:

/* Thermometer Connections (At your choice) */
#define THERM_PORT PORTD
#define THERM_DDR DDRD
#define THERM_PIN PIND
#define THERM_DQ PD0
/* Utils */
#define THERM_INPUT_MODE()     THERM_DDR&=~(1<<THERM_DQ)
#define THERM_OUTPUT_MODE()    THERM_DDR|=(1<<THERM_DQ)
#define THERM_LOW()       THERM_PORT&=~(1<<THERM_DQ)
#define THERM_HIGH()       THERM_PORT|=(1<<THERM_DQ)

#define THERM_CMD_CONVERTTEMP 0x44
#define THERM_CMD_RSCRATCHPAD 0xbe
#define THERM_CMD_WSCRATCHPAD 0x4e
#define THERM_CMD_CPYSCRATCHPAD 0x48
#define THERM_CMD_RECEEPROM 0xb8
#define THERM_CMD_RPWRSUPPLY 0xb4
#define THERM_CMD_SEARCHROM 0xf0
#define THERM_CMD_READROM 0x33
#define THERM_CMD_MATCHROM 0x55
#define THERM_CMD_SKIPROM 0xcc
#define THERM_CMD_ALARMSEARCH 0xec

#define THERM_DECIMAL_STEPS_12BIT 625 //.0625
#define THERM_DECIMAL_STEPS_9BIT 50 //.5



uint8_t therm_reset(){

  uint8_t i;

  //Pull line low and wait for 480uS
  THERM_LOW();
  THERM_OUTPUT_MODE();
  _delay_us(480);

  //Release line and wait for 60uS
  THERM_INPUT_MODE();
  _delay_us(60);

  //Store line value and wait until the completion of 480uS period
  i=(THERM_PIN & (1<<THERM_DQ));
  _delay_us(420);

  //Return the value read from the presence pulse (0=OK, 1=WRONG)
  return i;
}

void therm_write_bit(uint8_t bit){

  //Pull line low for 1uS
  THERM_LOW();
  THERM_OUTPUT_MODE();
  _delay_us(1);

  //If we want to write 1, release the line (if not will keep low)
  if(bit) THERM_INPUT_MODE();

  //Wait for 60uS and release the line
  _delay_us(60);
  THERM_INPUT_MODE();
}

uint8_t therm_read_bit(void){

  uint8_t bit=0;

  //Pull line low for 1uS
  THERM_LOW();
  THERM_OUTPUT_MODE();
  _delay_us(1);

  //Release line and wait for 14uS
  THERM_INPUT_MODE();
  _delay_us(14);

  //Read line value
  if(THERM_PIN&(1<<THERM_DQ)) bit=1;

  //Wait for 45uS to end and return read value
  _delay_us(45);
  return bit;
}

uint8_t therm_read_byte(void){
  uint8_t i=8, n=0;
  while(i--){
    //Shift one position right and store read value
    n>>=1;
    n|=(therm_read_bit()<<7);
  }
  return n;
}

void therm_write_byte(uint8_t byte){

  uint8_t i=8;

  while(i--){
    //Write actual bit and shift one position right to make the next bit ready
    therm_write_bit(byte&1);
    byte>>=1;
  }
}



void therm_read_temperature(char *buffer){

  // Buffer length must be at least 12bytes long! ["+XXX.XXXX C"]
  uint8_t temperature[2];
  int8_t digit;
  uint16_t decimal;

  //Reset, skip ROM and start temperature conversion
  therm_reset();
  therm_write_byte(THERM_CMD_SKIPROM);
  therm_write_byte(THERM_CMD_CONVERTTEMP);


  //Wait until conversion is complete
  while(!therm_read_bit());

  //Reset, skip ROM and send command to read Scratchpad
  therm_reset();
  therm_write_byte(THERM_CMD_SKIPROM);
  therm_write_byte(THERM_CMD_RSCRATCHPAD);

  //Read Scratchpad (only 2 first bytes)
  temperature[0]=therm_read_byte();
  temperature[1]=therm_read_byte();
  therm_reset();

  //Store temperature integer digits and decimal digits
  digit=temperature[0]>>4;
  digit|=(temperature[1]&0x7)<<2;

  //Store decimal digits
  decimal=temperature[0]&0xf;
  decimal*=THERM_DECIMAL_STEPS_12BIT;

  //Format temperature into a string [+XXX.XXXX C]
  sprintf(buffer, "%2d.%04uC", digit, decimal);

  lcd_txt(1, 1, buffer);
}

Das Problem das ich habe ist, dass meiner Sensor mir nur 1 zurückgibt. 
Die beiden Register in denen die Daten für die Temperatur stehen, sind 
gefüllt mit 1. Beziehungsweise kommt das an meinem Mikrocontroller an.

Die Fragen die ich mir stelle sind:
1. Wir haben noch einen Pull-Up Widerstand mit 4,7kOhm eingebaut. Muss 
der bei den Paket vom Conrad auch noch eingebaut werden, oder ist der 
schon mit dabei.

2. Muss ich den Sensor irgendwie aktivieren bevor ich Daten von ihm 
bekommen kann?

Bitte um schnelle Hilfe. Das Teil muss bis morgen funktionieren :-/

Gruß Tarlar