Datasheet

Operation Examples
Example 1
In Table 4 there are multiple devices on the bus using
parasite power. The bus master initiates a temperature
conversion in a specific MAX31820 and then reads its
scratchpad and recalculates the CRC to verify the data.
Example 2
In Table 5 there is only one device on the bus using
parasite power. The master writes to the T
H
, T
L
, and
configuration registers in the device’s scratchpad and
then reads the scratchpad and recalculates the CRC to
verify the data. The master then copies the scratchpad
contentstoEEPROM.
Table 4. Operation Example 1
Table 5. Operation Example 2
MASTER
MODE
DATA
(LSB FIRST)
COMMENTS
Tx Reset Master issues reset pulse.
Rx Presence
Devicesrespondwithpresencepulse.
Tx 55h Master issues Match ROM command for desired address.
Tx 64-bit ROM code Master sends device 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
Devicesrespondwithpresencepulse.
Tx 55h Master issues Match ROM command.
Tx 64-bit ROM code Master sends device 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8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
Devicerespondswithpresencepulse.
Tx CCh MasterissuesSkipROMcommand.
Tx 4Eh MasterissuesWriteScratchpadcommand.
Tx 3 data bytes Master sends 3 data bytes to the scratchpad (T
H
, T
L
,andcongurationregisters).
Tx Reset Master issues reset pulse.
Rx Presence
Device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8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
Device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.
MAX31820 1-Wire Ambient Temperature Sensor
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