DS18B20

6 of 22

Figure 4. Supplying the Parasite-Powered DS18B20 During Temperature Conversions

Figure 5. Powering the DS18B20 with an External Supply

64-BIT LASERED ROM CODE

Each DS18B20 contains a unique 64–bit code (see Figure 6) stored in ROM. The least significant 8 bits

of the ROM code contain the DS18B20’s 1-Wire family code: 28h. The next 48 bits contain a unique

serial number. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is

calculated from the first 56 bits of the ROM code. A detailed explanation of the CRC bits is provided in

the CRC Generation section. The 64-bit ROM code and associated ROM function control logic allow the

DS18B20 to operate as a 1-Wire device using the protocol detailed in the 1-Wire Bus System section.

Figure 6. 64-Bit Lasered ROM Code

8-BIT CRC

48-BIT SERIAL NUMBER

8-BIT FAMILY CODE (28h)

MSB

MSB

LSB

LSB

LSB

MSB

4.7k

1-Wire BUS

μP

DS18B20

GND

DQ

TO OTHER

1-WIRE DEVICES

DS18B20

GND

DQ

4.7k

TO OTHER

1-WIRE DEVICES

1-Wire BUS

μP