Datasheet

Operation Examples
Example 1
In Table 4 there are multiple devices on the bus. The bus
master initiates a temperature conversion in a specific
MAX31820PAR and then reads its scratchpad and recal-
culates the CRC to verify the data.
Example 2
In Table 5 there is only one device on the bus. 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.
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.
MAX31820PAR 1-Wire, Parasite-Power,
Ambient Temperature Sensor
www.maximintegrated.com
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