18B20 データシートの表示（PDF） - Maxim Integrated

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18B20

Programmable Resolution 1-Wire Digital Thermometer

Maxim Integrated 

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 (TH and TL)

and configuration register. Note that if the DS18B20 alarm function is not used, the TH and TL 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 TH and TL 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 TH, TL 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

the scratchpad at any time using the Recall E2 [B8h] command. The master can issue read time slots

following the Recall E2 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

Byte 0

Byte 1

SCRATCHPAD

(POWER-UP STATE)

Temperature LSB (50h) (85°C)

Temperature MSB (05h)

Byte 2 TH Register or User Byte 1*

Byte 3 TL 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

TH Register or User Byte 1

TL Register or User Byte 2

Configuration Register

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