Datasheet

DS18B20 Operation Example 1
In this example there are multiple DS18B20s on the bus
and they are using parasite power. The bus master initi-
ates a temperature conversion in a specific DS18B20 and
then reads its scratchpad and recalculates the CRC to
verify the data.
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)
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
conversion (t
CONV
).
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
rst 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
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
Master sends three data bytes
to scratchpad (T
H
, T
L
, and
cong).
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
rst 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.
DS18B20 Programmable Resolution
1-Wire Digital Thermometer
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