DS18B20
MEMORY
The DS18B20’s memory is organized as shown in Figure 7. The memory consists of an SRAM
scratchpad with nonvolatile EEPROM storage for the high and low alarm trigger registers (T
H
and T
L
)
and configuration register. Note that if the DS18B20 alarm function is not used, the T
H
and T
L
registers
can serve as general-purpose memory. All memory commands are described in detail in the
DS18B20
Function Commands
section.
Byte 0 and byte 1 of the scratchpad contain the LSB and the MSB of the temperature register,
respectively. These bytes are read-only. Bytes 2 and 3 provide access to T
H
and T
L
registers. Byte 4
contains the configuration register data, which is explained in detail in the
Configuration Register
section.
Bytes 5, 6, and 7 are reserved for internal use by the device and cannot be overwritten.
Byte 8 of the scratchpad is read-only and contains the CRC code for bytes 0 through 7 of the scratchpad.
The DS18B20 generates this CRC using the method described in the
CRC Generation
section.
Data is written to bytes 2, 3, and 4 of the scratchpad using the Write Scratchpad [4Eh] command; the data
must be transmitted to the DS18B20 starting with the least significant bit of byte 2. To verify data
integrity, the scratchpad can be read (using the Read Scratchpad [BEh] command) after the data is
written. When reading the scratchpad, data is transferred over the 1-Wire bus starting with the least
significant bit of byte 0. To transfer the T
H
, T
L
and configuration data from the scratchpad to EEPROM,
the master must issue the Copy Scratchpad [48h] command.
Data in the EEPROM registers is retained when the device is powered down; at power-up the EEPROM
data is reloaded into the corresponding scratchpad locations. Data can also be reloaded from EEPROM to
2
the scratchpad at any time using the Recall E [B8h] command. The master can issue read time slots
following the Recall E
2
command and the DS18B20 will indicate the status of the recall by transmitting 0
while the recall is in progress and 1 when the recall is done.
Figure 7. DS18B20 Memory Map
SCRATCHPAD
(POWER-UP STATE
)
Byte 0 Temperature LSB (50h)
(85°C)
Byte 1 Temperature MSB (05h)
Byte 2 T
H
Register or User Byte 1*
Byte 3 T
L
Register or User Byte 2*
Byte 4 Configuration Register*
Byte 5 Reserved (FFh)
Byte 6 Reserved
Byte 7 Reserved (10h)
Byte 8 CRC*
*
Power-up state depends on value(s) stored in EEPROM.
EEPROM
T
H
Register or User Byte 1
T
L
Register or User Byte 2
Configuration Register
7 of 22
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
