DS18B20
Figure 4. Supplying the Parasite-Powered DS18B20 During Temperature Conversions
VPU
DS18B20
GND
DQ VDD
VPU
µP
4.7k
TO OTHER
1-WIRE DEVICES
1-Wire BUS
Figure 5. Powering the DS18B20 with an External Supply
VDD (EXTERNAL SUPPLY)
TO OTHER
DS18B20
VPU
µP
GND
DQ VDD
4.7k
1-Wire BUS
1-WIRE DEVICES
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 LSB
MSB
LSB MSB
LSB
6 of 22
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
