Datasheet

Note 1: The master must enable a strong pullup on the 1-Wire bus during temperature conversions and copies from the scratchpad
toEEPROM.Nootherbusactivitycantakeplaceduringthistime.
Note 2: The master can interrupt the transmission of data at any time by issuing a reset.
Note 3: All 3 bytes must be written before a reset is issued.
MAX31820PAR Function Commands
After the bus master has used a ROM command to
address the device with which it wishes to communi-
cate, the master can issue one of the device function
commands. These commands allow the master to write
to and read from the device’s scratchpad memory,
initiate temperature conversions, and determine the
power-supply mode. Table 3 summarizes the device
function commands, and
Figure7 illustrates the function
commands.
Convert T [44h]
This command initiates a single temperature conversion.
Following the conversion, the resulting thermal data is
stored in the 2-byte temperature register in the scratch-
pad memory and the device returns to its low-power idle
state. Within 10µs (max) after this command is issued, the
master must enable a strong pullup on the 1-Wire bus for
the duration of the conversion (t
CONV
), as described in
the Parasite Power section.
Write Scratchpad [4Eh]
This command allows the master to write 3 bytes of data
to the device’s scratchpad. The first data byte is written
into the T
H
register (byte 2 of the scratchpad), the second
byte is written into the T
L
register (byte 3), and the third
byteiswrittenintotheconfigurationregister(byte4).Data
must be transmitted least significant bit first. All three
bytes must be written before the master issues a reset,
or the data may be corrupted.
Read Scratchpad [BEh]
This command allows the master to read the contents
of the scratchpad. The data transfer starts with the least
significant bit of byte 0 and continues through the scratch-
pad until the 9th byte (byte 8 – CRC) is read. The master
can issue a reset to terminate reading at any time if only
part of the scratchpad data is needed.
Copy Scratchpad [48h]
This command copies the contents of the scratchpad
T
H
, T
L
and configuration registers (bytes 2, 3, and 4)
to EEPROM. Within 10µs (max) after this command is
issued, the master must enable a strong pullup on the
1-Wire bus for at least 10ms as described in the Parasite
Power section.
Recall E
2
[B8h]
This command recalls the alarm trigger values (T
H
and
T
L
) and configuration data from EEPROM and places the
data in bytes 2, 3, and 4, respectively, in the scratchpad
memory. The master device can issue read time slots fol-
lowing the Recall E
2
command and the device indicates
the status of the recall by transmitting 0 while the recall
is in progress and 1 when the recall is done. The recall
operation happens automatically at power-up, so valid
data is available in the scratchpad as soon as power is
applied to the device.
Table 3. MAX31820PAR Function Command Set
COMMAND DESCRIPTION PROTOCOL
1-Wire BUS ACTIVITY AFTER COMMAND IS
ISSUED
Convert T
(Note1)
Initiates temperature conversion. 44h None.
ReadScratchpad
(Note2)
Reads the entire scratchpad
including the CRC byte.
BEh The device transmits up to 9 data bytes to master.
WriteScratchpad
(Note3)
Writes to scratchpad bytes 2, 3,
and 4 (T
H
, T
L
,andconguration
registers).
4Eh The master transmits 3 data bytes to the device.
CopyScratchpad
(Note1)
Copies T
H
, T
L
,andconguration
register data from the scratchpad to
EEPROM.
48h None.
Recall E
2
Recalls T
H
, T
L
,andconguration
register data from EEPROM to the
scratchpad.
B8h The device transmits recall status to the master.
MAX31820PAR 1-Wire, Parasite-Power,
Ambient Temperature Sensor
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