Datasheet

in Figure 1. The 1-Wire bus must be switched to the
strong pullup within 10µs (max) after a Convert T [44h] or
CopyScratchpad[48h]commandisissued,andthebus
must be held high by the pullup for the duration of the
conversion (t
CONV
) or data transfer (t
WR
 = 10ms). No
other activity can take place on the 1-Wire bus while the
pullup is enabled.
64-Bit Lasered ROM Code
Each device contains a unique 64-bit code stored in
ROM (
Figure2). The least significant 8 bits of the ROM
code contain the device’s 1-Wire family code, 28h. The
next 48 bits contain a unique serial number. The most
significant 8 bits contain a cyclic-redundancy-check (CRC)
byte that is calculated from the first 56 bits of the ROM
code. A detailed explanation of the CRC bits is provided
in the CRC Generation section. The 64-bit ROM code and
associated ROM function control logic allow the device to
operate as a 1-Wire device using the protocol detailed in
the 1-Wire Bus System section.
Memory
The device’s memory is organized as shown in
Figure3.ThememoryconsistsofanSRAMscratchpadwith
nonvolatile EEPROM storage for the high and low alarm
trigger 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 memory commands are described in detail in the
MAX31820PAR 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.
Figure 2. 64-Bit Lasered ROM Code
Figure 3. Memory Map
MSb
8-BIT
CRC CODE
48-BIT SERIAL NUMBER
MSb MSbLSb
LSb
LSb
8-BIT FAMILY CODE
(28h)
MSbLSb
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
MAX31820PAR 1-Wire, Parasite-Power,
Ambient Temperature Sensor
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