DS18S20 Datasheet, PDF (7/23 Pages) Dallas Semiconductor – High Precision 1-Wire Digital Thermometer

DS18S20
MEMORY
The DS18S20’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).
Note that if the DS18S20 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 DS18S20 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. Bytes 4 and
5 are reserved for internal use by the device and cannot be overwritten; these bytes will return all 1s when
read. Bytes 6 and 7 contain the COUNT REMAIN and COUNT PER ºC registers, which can be used to
calculate extended resolution results as explained in the Operation—Measuring Temperature section.
Byte 8 of the scratchpad is read-only and contains the CRC code for bytes 0 through 7 of the scratchpad.
The DS18S20 generates this CRC using the method described in the CRC Generation section.
Data is written to bytes 2 and 3 of the scratchpad using the Write Scratchpad [4Eh] command; the data
must be transmitted to the DS18S20 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 and T_L 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
the scratchpad at any time using the Recall E² [B8h] command. The master can issue “read-time slots”
(see the 1-Wire Bus System section) following the Recall E² command and the DS18S20 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. DS18S20 Memory Map
Byte 0
Byte 1
SCRATCHPAD
(POWER-UP STATE)
Temperature LSB (AAh)
(85°C)
Temperature MSB (00h)
Byte 2 T_H Register or User Byte 1*
Byte 3 T_L Register or User Byte 2*
Byte 4 Reserved (FFh)
Byte 5 Reserved (FFh)
Byte 6 COUNT REMAIN (0Ch)
Byte 7 COUNT PER °C (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
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