DS1822

7 of 21

MEMORY

The DS1822’s memory is organized as shown in Figure 7. The memory consists of an SRAM scratchpad

purpose memory. All memory commands are described in detail in the DS1822 FUNCTION

COMMANDS section.

Byte 0 and byte 1 of the scratchpad contain the LSB and the MSB of the temperature register,

contains the configuration register data, which is explained in detail in the CONFIGURATION

REGISTER section of this data sheet. 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 cyclic redundancy check (CRC) code for bytes 0

through 7 of the scratchpad. The DS1822 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 DS1822 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

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 E

2

[B8h] command. The master can issue read time slots

following the Recall E

while the recall is in progress and 1 when the recall is done.

DS1822 MEMORY MAP Figure 7

SCRATCHPAD (Power-up State)

byte 0

Temperature LSB (50h)

byte 1

Temperature MSB (05h)

EEPROM

byte 2

byte 3

byte 4

Configuration Register*

Configuration Register

byte 5

Reserved (FFh)

byte 6

Reserved

byte 7

Reserved (10h)

byte 8 CRC*

in EEPROM

(85°C)