DS18B20_07 Datasheet, PDF(18/21 Page) Dallas Semiconductor – Programmable Resolution 1-Wire Digital Thermometer

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DS18B20_07 Datasheet, PDF (18/21 Pages) Dallas Semiconductor – Programmable Resolution 1-Wire Digital Thermometer

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DS18B20

DS18B20 OPERATION EXAMPLE 1

In this example there are multiple DS18B20s on the bus and they are using parasite power. The bus

master initiates a temperature conversion in a specific DS18B20 and then reads its scratchpad and

recalculates the CRC to verify the data.

MASTER MODE

DATA (LSB FIRST)

Reset

Presence

55h

64-bit ROM code

44h

DQ line held high by

strong pullup

Reset

Presence

55h

64-bit ROM code

BEh

9 data bytes

COMMENTS

Master issues reset pulse.

DS18B20s respond with presence pulse.

Master issues Match ROM command.

Master sends DS18B20 ROM code.

Master issues Convert T command.

Master applies strong pullup to DQ for the duration of the

conversion (tconv).

Master issues reset pulse.

DS18B20s respond with presence pulse.

Master issues Match ROM command.

Master sends DS18B20 ROM code.

Master issues Read Scratchpad command.

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.

DS18B20 OPERATION EXAMPLE 2

In this example there is only one DS18B20 on the bus and it is using parasite power. The master writes to

the TH, TL, and configuration registers in the DS18B20 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)

Reset

Presence

CCh

4Eh

3 data bytes

Reset

Presence

CCh

BEh

9 data bytes

Reset

Presence

CCh

48h

DQ line held high by

strong pullup

COMMENTS

Master issues reset pulse.

DS18B20 responds with presence pulse.

Master issues Skip ROM command.

Master issues Write Scratchpad command.

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

Master issues reset pulse.

DS18B20 responds with presence pulse.

Master issues Skip ROM command.

Master issues Read Scratchpad command.

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.

Master issues reset pulse.

DS18B20 responds with presence pulse.

Master issues Skip ROM command.

Master issues Copy Scratchpad command.

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

operation is in progress.

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