DS1822-PAR

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Data is written to bytes 2, 3, and 4 of the scratchpad using the Write Scratchpad [4Eh] command, and the

data must be transmitted to the DS1822-PAR 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

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 E

2

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

(see the 1-WIRE BUS SYSTEM section) following the Recall E

indicate the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is

done.

CONFIGURATION REGISTER

Byte 4 of the scratchpad memory contains the configuration register, which is organized as

illustrated in Figure 7. The user can set the conversion resolution of the DS1822-PAR using the R0 and

R1 bits in this register as shown in Table 3. The power-up default of these bits is R0 = 1 and R1 = 1 (12-

bit resolution). Note that there is a direct tradeoff between resolution and conversion time. Bit 7 and bits

0-4 in the configuration register are reserved for internal use by the device and cannot be overwritten.

CONFIGURATION REGISTER Figure 7

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

0

R1

R0

1

1

1

1

1

THERMOMETER RESOLUTION CONFIGURATION Table 3

R1

R0

Resolution

Max Conversion Time

0

0

9-bit

93.75 ms

0

1

10-bit

187.5 ms

1

0

11-bit

375 ms

1

1

12-bit

750 ms

CRC GENERATION

CRC bytes are provided as part of the DS1822-PAR’s 64-bit ROM code and in the 9

scratchpad memory. The ROM code CRC is calculated from the first 56 bits of the ROM code and is

contained in the most significant byte of the ROM. The scratchpad CRC is calculated from the data stored

in the scratchpad, and therefore it changes when the data in the scratchpad changes. The CRCs provide

the bus master with a method of data validation when data is read from the DS1822-PAR. To verify that

data has been read correctly, the bus master must recalculate the CRC from the received data and then

compare this value to either the ROM code CRC (for ROM reads) or to the scratchpad CRC (for

scratchpad reads). If the calculated CRC matches the read CRC, the data has been received error free. The

comparison of CRC values and the decision to continue with an operation are determined entirely by the

bus master. There is no circuitry inside the DS1822-PAR that prevents a command sequence from