DS1822 datasheet(17/20 Pages) DALLAS

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DS1822

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DS1822 OPERATION EXAMPLE 1

In this example there are multiple DS1822s on the bus and they are using parasite power. The bus master

initiates a temperature conversion in a specific DS1822 and then reads its scratchpad and recalculates the

CRC to verify the data.

MASTER MODE

DATA (LSB FIRST)

COMMENTS

Reset

Master issues reset pulse.

Presence

DS1822s respond with presence pulse.

55h

Master issues Match ROM command.

64-bit ROM code

Master sends DS1822 ROM code.

44h

Master issues Convert T command.

DQ line held high by

strong pullup

Master applies strong pullup to DQ for the duration of the

conversion (tconv).

Reset

Master issues reset pulse.

Presence

DS1822s respond with presence pulse.

55h

Master issues Match ROM command.

64-bit ROM code

Master sends DS1822 ROM code.

BEh

Master issues Read Scratchpad command.

9 data bytes

Master reads entire scratchpad including CRC. The master

then recalculates the CRC of the first eight data bytes from the

scratchpad and compares the calculated CRC with the read

CRC (byte 9). If they match, the master continues; if not, the

read operation is repeated.

DS1822 OPERATION EXAMPLE 2

In this example there is only one DS1822 on the bus and it is using parasite power. The master writes to

the TH, TL, and configuration registers in the DS1822 scratchpad and then reads the scratchpad and

recalculates the CRC to verify the data. The master then copies the scratchpad contents to EEPROM.

MASTER MODE

DATA (LSB FIRST)

COMMENTS

Reset

Master issues reset pulse.

Presence

DS1822 responds with presence pulse.

CCh

Master issues Skip ROM command.

4Eh

Master issues Write Scratchpad command.

3 data bytes

Master sends three data bytes to scratchpad (TH, TL, and config).

Reset

Master issues reset pulse.

Presence

DS1822 responds with presence pulse.

CCh

Master issues Skip ROM command.

BEh

Master issues Read Scratchpad command.

9 data bytes

Master reads entire scratchpad including CRC. The master then

recalculates the CRC of the first eight data bytes from the

scratchpad and compares the calculated CRC with the read CRC

(byte 9). If they match, the master continues; if not, the read

operation is repeated.

Reset

Master issues reset pulse.

Presence

DS1822 responds with presence pulse.

CCh

Master issues Skip ROM command.

48h

Master issues Copy Scratchpad command.

DQ line held high by

strong pullup

Master applies strong pullup to DQ for at least 10ms while copy

operation is in progress.

DS1822 Datasheet(PDF) 17 Page - Dallas Semiconductor

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