Datasheet

Memory
The device’s memory is organized as shown in Figure4.
The memoryconsistsof an SRAMscratchpadwith non-
volatileEEPROMstorageforthehighandlowalarmtrig-
ger registers (T
H
and T
L
)andconfigurationregister.Note
that if the device alarm function is not used, the T
H
and T
L
registers can serve as general-purpose memory. All mem-
ory commands are described in detail in the MAX31820
Function Commands section.
Byte0andbyte1ofthescratchpadcontaintheLSBand
theMSBof thetemperatureregister,respectively.These
bytesareread-only.Bytes2and3provideaccesstoT
H
and T
L
registers.Byte4containstheconfigurationregis-
ter data, which is explained in detail in the Configuration
Register
section.Bytes7:5arereservedforinternaluseby
thedeviceandcannotbeoverwritten.Byte8ofthescratch-
padisread-onlyandcontainstheCRCcodeforbytes7:0
of the scratchpad. The device generates this CRC using
the method described in the CRC Generation section.
Datais writtentobytes4:2ofthescratchpadusing the
Write Scratchpad [4Eh] command; the data must be
transmitted to the device starting with the least significant
bit of byte 2. To verify data integrity, the scratchpad can
be read (using the Read Scratchpad [BEh] command)
after the data is written. When reading the scratchpad,
data is transferred over the 1-Wire bus starting with the
least significant bit of byte 0. To transfer the T
H
, T
L
, and
configurationdatafromthescratchpadtoEEPROM,the
mastermustissuetheCopyScratchpad[48h]command.
Data in the EEPROM registers is retained when the
deviceispowereddown;atpower-uptheEEPROMdata
is reloaded into the corresponding scratchpad locations.
DatacanalsobereloadedfromEEPROMtothescratch-
pad at any time using the Recall E
2
[B8h]command.The
master can issue read time slots following 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.
Conguration Register
Byte4ofthescratchpadmemorycontainstheconfigura-
tion register, which is organized as shown in Configuration
Register Format. The user can set the conversion resolu-
tion of the device using the R0 and R1 bits in this register,
as shown in Table 2. The power-up default of these bits is
R0=1andR1=1(12-bitresolution).Notethatthereis
a direct trade-off between resolution and conversion time.
Bit7andbits4:0intheconfigurationregisterarereserved
for internal use by the device and cannot be overwritten.
Conguration Register Format
Figure 4. Memory Map
TEMPERATURE REGISTER LSB (50h)BYTE 0
TEMPERATURE REGISTER MSB (05h)BYTE 1
T
H
REGISTER OR USER BYTE 1*BYTE 2
T
L
REGISTER OR USER BYTE 2*BYTE 3
CONFIGURATION REGISTER*BYTE 4
RESERVED (FFh)BYTE 5
RESERVEDBYTE 6
RESERVED (10h)BYTE 7
CRC*BYTE 8
*POWER-UP STATE DEPENDS ON VALUE(S) STORED IN EEPROM.
SCRATCHPAD (POWER-UP STATE
SHOWN IN PARENTHESES)
EEPROM
T
H
REGISTER OR USER BYTE 1
T
L
REGISTER OR USER BYTE 2
CONFIGURATION REGISTER
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0 R1 R0 1 1 1 1 1
MAX31820 1-Wire Ambient Temperature Sensor
www.maximintegrated.com
Maxim Integrated │ 9