DS18B20

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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)

COMMENTS

Tx

Reset

Master issues reset pulse.

Rx

Presence

DS18B20s respond with presence pulse.

Tx

55h

Master issues Match ROM command.

Tx

64-bit ROM code

Master sends DS18B20 ROM code.

Tx

44h

Master issues Convert T command.

Tx

DQ line held high by

strong pullup

Master applies strong pullup to DQ for the duration of the

Tx

Reset

Master issues reset pulse.

Rx

Presence

DS18B20s respond with presence pulse.

Tx

55h

Master issues Match ROM command.

Tx

64-bit ROM code

Master sends DS18B20 ROM code.

Tx

BEh

Master issues Read Scratchpad command.

Rx

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.

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

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

MASTER MODE

DATA (LSB FIRST)

COMMENTS

Tx

Reset

Master issues reset pulse.

Rx

Presence

DS18B20 responds with presence pulse.

Tx

CCh

Master issues Skip ROM command.

Tx

4Eh

Master issues Write Scratchpad command.

Tx

3 data bytes

Tx

Reset

Master issues reset pulse.

Rx

Presence

DS18B20 responds with presence pulse.

Tx

CCh

Master issues Skip ROM command.

Tx

BEh

Master issues Read Scratchpad command.

Rx

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.

Tx

Reset

Master issues reset pulse.

Rx

Presence

DS18B20 responds with presence pulse.

Tx

CCh

Master issues Skip ROM command.

Tx

48h

Master issues Copy Scratchpad command.

Tx

DQ line held high by

strong pullup

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

operation is in progress.