Datasheet

DS18S20
6 of 23
Figure 4. Supplying the Parasite-Powered DS18S20 During Temperature Conversions
Figure 5. Powering the DS18S20 with an External Supply
64-BIT LASERED ROM CODE
Each DS18S20 contains a unique 64-bit code (see Figure 6) stored in ROM. The least significant 8 bits of
the ROM code contain the DS18S20’s 1-Wire family code: 10h. 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
DS18S20 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 (10h)
V
PU
V
PU
4.7k
1-Wire BUS
µ
P
DS18S20
GND
V
DD
DQ
TO OTHER
1-WIRE DEVICES
V
DD
(EXTERNAL SUPPLY)
DS18S20
GND
V
DD
DQ
V
PU
4.7k
TO OTHER
1-WIRE DEVICES
1-Wire BUS
µ
P
MSB
MSB
LSB
LSB
LSB
MSB