MAX31820PARMCR+T [MAXIM]
Serial Switch/Digital Sensor, 12 Bit(s), 2Cel, Oval, 3 Pin, Through Hole Mount, ROHS COMPLIANT, TO-92, 3 PIN;
| 型号： | MAX31820PARMCR+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Serial Switch/Digital Sensor, 12 Bit(s), 2Cel, Oval, 3 Pin, Through Hole Mount, ROHS COMPLIANT, TO-92, 3 PIN 输出元件 传感器 换能器 |
| 文件： | 总21页 (文件大小：861K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
General Description
Benefits and Features
●ꢀ Uniqueꢀ1-WireꢀInterfaceꢀRequiresꢀOnlyꢀOneꢀPortꢀPinꢀ
The MAX31820PAR ambient temperature sensor pro-
vides 9-bit to 12-bit Celsius temperature measurements
with ±0.5°C accuracy over a +10°C to +45°C temperature
range. Over its entire -55°C to +125°C operating range,
the device has ±2.0°C accuracy.
for Communication
●ꢀ DerivesꢀPowerꢀfromꢀDataꢀLineꢀ(ParasiteꢀPower);ꢀNoꢀ
LocalꢀPowerꢀSupplyꢀNeeded
®
The device communicates over a 1-Wire bus that, by
●ꢀ MultidropꢀCapabilityꢀSimplifiesꢀDistributedꢀ
Temperature-SensingꢀApplicationsꢀ
definition, requires only one data line (and ground) for
communication with a central microprocessor. In addi-
tion, the device derives power directly from the data line
(“parasite power”), eliminating the need for an external
power supply. Requiring so few pins enables the device
to be placed in a 3-pin TO-92 package. The form factor
of this package allows the device to be placed above
the board and thus measure the ambient temperature of
a system, as opposed to the board temperature that a
surface-mount package would measure.
●ꢀ RequiresꢀNoꢀExternalꢀComponents
●ꢀ MeasuresꢀTemperaturesꢀfromꢀ-55°Cꢀtoꢀ+125°Cꢀ(-67°Fꢀ
toꢀ+257°F)
●ꢀ ±0.5°CꢀAccuracyꢀfromꢀ+10°Cꢀtoꢀ+45°C
●ꢀ ThermometerꢀResolutionꢀisꢀUser-Selectableꢀfromꢀ
9ꢀBitsꢀtoꢀ12ꢀBits
●ꢀ ConvertsꢀTemperatureꢀtoꢀ12-BitꢀDigitalꢀWordꢀinꢀ
750msꢀ(Max)
Each MAX31820PAR has a unique 64-bit serial code, which
allows multiple MAX31820PAR devices to function on the
same 1-Wire bus. Therefore, it is simple to use one micropro-
cessor to control many devices distributed over a large area.
●ꢀ User-DefinableꢀNonvolatileꢀ(NV)ꢀAlarmꢀSettings
●ꢀ AlarmꢀSearchꢀCommandꢀIdentifiesꢀandꢀAddressesꢀ
DevicesꢀWhoseꢀTemperatureꢀisꢀOutsideꢀProgrammedꢀ
Limitsꢀ(TemperatureꢀAlarmꢀCondition)
Applications
●ꢀ HVACꢀEnvironmentalꢀControls
●ꢀ TemperatureꢀMonitoringꢀSystemsꢀInsideꢀBuildings,ꢀ
Equipment, or Machinery
●ꢀ Availableꢀinꢀ3-PinꢀTO-92ꢀPackage
●ꢀ SoftwareꢀCompatibleꢀwithꢀtheꢀDS1822-PARꢀandꢀ
DS18B20-PAR
●ꢀ ProcessꢀMonitoringꢀandꢀControlꢀSystems
●ꢀ ThermostaticꢀControls
●ꢀ IndustrialꢀSystems
●ꢀ ConsumerꢀProducts
●ꢀ Thermometers
●ꢀ AnyꢀThermallyꢀSensitiveꢀSystem
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part, refer
to www.maximintegrated.com/MAX31820PAR.related.
Block Diagram
V
PU
PARASITE-POWER
CIRCUIT
MEMORY
CONTROL LOGIC
4.7kΩ
MAX31820PAR
DQ
TEMPERATURE REGISTER
64-BIT ROM
AND
ALARM HIGH TRIGGER (T )
H
REGISTER (EEPROM)
1-Wire PORT
C
PP
SCRATCHPAD
ALARM LOW TRIGGER (T )
L
REGISTER (EEPROM)
CONFIGURATION REGISTER (EEPROM)
8-BIT CRC GENERATOR
GND
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
19-6732; Rev 0; 6/13
MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Absolute Maximum Ratings
VoltageꢀRangeꢀonꢀAnyꢀPinꢀRelativeꢀtoꢀGround....-0.5Vꢀtoꢀ+6.0V
Operating Temperature Range......................... -55°C to +100°C
StorageꢀTemperatureꢀRange............................ -55°C to +125°C
SolderingꢀTemperatureꢀ(reflow).......................................+260°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
DC Electrical Characteristics
(V ꢀ=ꢀ3.0Vꢀtoꢀ3.7V,ꢀT ꢀ=ꢀ-55°Cꢀtoꢀ+100°C,ꢀunlessꢀotherwiseꢀnoted.)ꢀ(Noteꢀ1)
PU
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
3.7
0.5
2
UNITS
PullupꢀSupplyꢀVoltage
V
(Notesꢀ2,ꢀ3)
3.0
V
PU
+10°C to +45°C
-55°C to +100°C
(Notesꢀ2,ꢀ4,ꢀ5)
(Notesꢀ2,ꢀ6)
Thermometer Error
T
°C
ERR
InputꢀLogic-Low
InputꢀLogic-High
SinkꢀCurrent
Active Current
DQꢀInputꢀCurrent
Drift
V
-0.3
3.0
4.0
+0.8
3.7
V
IL
IH
L
V
V
I
V
ꢀ=ꢀ0.4Vꢀ(Noteꢀ2)
mA
mA
µA
°C
I/O
I
(Noteꢀ7)
(Noteꢀ8)
(Noteꢀ9)
1
1.5
DQA
I
5
DQ
0.2
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
AC Electrical Characteristics
(V ꢀ=ꢀ3.0Vꢀtoꢀ3.7V,ꢀT ꢀ=ꢀ-55°Cꢀtoꢀ+100°C,ꢀunlessꢀotherwiseꢀnoted.)ꢀ(Noteꢀ1)
PU
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
93.75
187.5
375
UNITS
9-bit resolution
10-bit resolution
11-bit resolution
12-bit resolution
Temperature Conversion Time
t
ms
CONV
750
StartꢀConvertꢀTꢀcommandꢀorꢀCopyꢀ
Scratchpadꢀcommandꢀissued
TimeꢀtoꢀStrongꢀPullupꢀOn
t
10
µs
SPON
TimeꢀSlot
t
(Noteꢀ10)
(Noteꢀ10)
(Noteꢀ10)
(Noteꢀ10)
(Noteꢀ10)
(Noteꢀ10)
(Notesꢀ10,ꢀ11)
(Noteꢀ10)
(Noteꢀ10)
60
1
120
µs
µs
µs
µs
µs
µs
µs
µs
µs
pF
SLOT
Recovery Time
t
REC
Write-ZeroꢀLowꢀTime
Write-OneꢀLowꢀTime
ReadꢀDataꢀValid
t
t
60
1
120
15
LOW0
LOW1
t
15
RDV
ResetꢀTimeꢀHigh
t
480
480
15
RSTH
ResetꢀTimeꢀLow
t
960
60
RSTL
Presence-DetectꢀHigh
Presence-DetectꢀLow
Capacitance
t
PDHIGH
t
60
240
25
PDLOW
C
IN/OUT
NONVOLATILE MEMORY
NonvolatileꢀWriteꢀCycleꢀTime
EEPROM Writes
t
2
10
ms
WR
N
-55°C to +55°C
-55°C to +55°C
50k
10
Writes
Years
EEWR
EEPROMꢀDataꢀRetention
t
EEDR
Note 1: Limitsꢀareꢀ100%ꢀtestedꢀatꢀT = +25°C and T ꢀ=ꢀ+85°C.ꢀLimitsꢀoverꢀtheꢀoperatingꢀtemperatureꢀrangeꢀandꢀrelevantꢀsupplyꢀ
A
A
voltage are guaranteed by design and characterization.
Note 2: All voltages are referenced to ground.
Note 3: The pullup supply voltage specification assumes that the pullup device (resistor or transistor) is ideal, and therefore the
highꢀlevelꢀofꢀtheꢀpullupꢀisꢀequalꢀtoꢀV .ꢀInꢀorderꢀtoꢀmeetꢀtheꢀdevice’sꢀV spec, the actual supply rail for the strong pullup
PU
IH
transistorꢀmustꢀincludeꢀmarginꢀforꢀtheꢀvoltageꢀdropꢀacrossꢀtheꢀtransistorꢀwhenꢀitꢀisꢀturnedꢀon;ꢀthus:ꢀV
ꢀ=ꢀV
PU_ACTUAL
PU_
ꢀ+ꢀV
.
IDEAL
TRANSISTOR
Note 4: Logic-lowꢀvoltagesꢀareꢀspecifiedꢀatꢀaꢀsinkꢀcurrentꢀofꢀ4mA.
Note 5: Toꢀguaranteeꢀaꢀpresenceꢀpulseꢀunderꢀlow-voltageꢀparasite-powerꢀconditions,ꢀV
0.5V.ꢀ
may have to be reduced to as low as
ILMAX
Note 6: Logic-highꢀvoltagesꢀareꢀspecifiedꢀatꢀaꢀsourceꢀcurrentꢀofꢀ1mA.
Note 7: Active current refers to supply current during active temperature conversions or EEPROM writes.
Note 8: DQꢀlineꢀisꢀhighꢀ(high-Zꢀstate).
Note 9: Driftꢀdataꢀisꢀbasedꢀonꢀaꢀ1000-hourꢀstressꢀtestꢀatꢀ+125°C.
Note 10: Seeꢀtheꢀ1-Wire Timing Diagrams.
Note 11: If t
> 960µs, a power-on reset may occur.
RSTL
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
1-Wire Timing Diagrams
1-Wire WRITE-ZERO TIME SLOT
START OF NEXT CYCLE
t
SLOT
t
REC
t
LOW0
1-Wire READ-ZERO TIME SLOT
t
START OF NEXT CYCLE
SLOT
t
REC
t
RDV
1-Wire RESET PULSE
RESET PULSE FROM HOST
t
t
RSTH
RSTL
1-Wire PRESENCE DETECT
PRESENCE DETECT
t
PDHIGH
t
PDLOW
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Pin Configuration
SIDE VIEW
FRONT VIEW
GND
DQ
1
2
3
1
2
3
MAX31820PAR
N.C.
TO-92
Pin Description
PIN
NAME
FUNCTION
1
GND
Ground
DataꢀInput/Output.ꢀOpen-drain,ꢀ1-Wireꢀinterfaceꢀpinꢀthatꢀprovidesꢀpowerꢀtoꢀtheꢀdeviceꢀwhenꢀusedꢀinꢀ
parasite power mode (see the Parasite Power section).
2
3
DQ
N.C.
NotꢀConnected.ꢀDoesꢀnotꢀconnectꢀtoꢀinternalꢀcircuit.
registers (T and T ) and the 1-byte configuration regis-
ter. The configuration register allows the user to set the
H
L
Detailed Description
The MAX31820PAR ambient temperature sensor
provides 9-bit to 12-bit Celsius temperature measure-
ments with ±0.5°C accuracy over a +10°C to +45°C tem-
perature range. Over its entire -55°C to +125°C operating
range, the device has ±2.0°C accuracy. The device com-
municates over a 1-Wire bus that, by definition, requires
only one data line (and ground) for communication with
a central microprocessor. In addition, the device derives
power directly from the data line (“parasite power”),
eliminating the need for an external power supply.
Requiring so few pins enables the device to be placed
in a 3-pin TO-92 package. The form factor of this pack-
age allows the device to be placed above the board and
thus measure the ambient temperature of a system, as
opposed to the board temperature that a surface-mount
package would measure.
resolution of the temperature-to-digital conversion to 9,
10, 11, or 12 bits. The T , T , and configuration registers
H
L
are nonvolatile (EEPROM), so they retain data when the
device is powered down.
The device uses Maxim Integrated’s exclusive 1-Wire
bus protocol that implements bus communication using
one control signal. The control line requires a weak pullup
resistor since all devices are linked to the bus through a
three-state or open-drain port (i.e., the MAX31820PAR’s
DQꢀ pin).ꢀ Inꢀ thisꢀ busꢀ system,ꢀ theꢀ microprocessorꢀ (theꢀ
master device) identifies and addresses devices on the
busꢀ usingꢀ eachꢀ device’sꢀ uniqueꢀ 64-bitꢀ code.ꢀ Becauseꢀ
each device has a unique code, the number of devices
that can be addressed on one bus is virtually unlimited.
The 1-Wire bus protocol, including detailed explanations
of the commands and time slots, is covered in the 1-Wire
Bus System section.
Each device has a unique 64-bit serial code, allowing
multiple MAX31820PAR devices to function on the same
1-Wire bus. Therefore, it is simple to use one micro-
processor to control many devices distributed over a
large area. The 64-bit ROM stores the device’s unique
serial code. The scratchpad memory contains the 2-byte
temperature register that stores the digital output from
the temperature sensor. In addition, the scratchpad pro-
vides access to the 1-byte upper and lower alarm trigger
The device can also operate without an external power
supply. Power is instead supplied through the 1-Wire
pullupꢀresistorꢀthroughꢀtheꢀDQꢀpinꢀwhenꢀtheꢀbusꢀisꢀhigh.ꢀ
The high bus signal also charges an internal capacitor
(C ), which then supplies power to the device when the
PP
bus is low. This method of deriving power from the 1-Wire
bus is referred to as “parasite power.”
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
other components to the sensor. As much as practical,
avoid copper in the vicinity of the sensor.
Operation
Measuring Ambient Temperature
The device’s core functionality is its direct-to-digital tem-
perature sensor. The resolution of the temperature sensor
is user-configurable to 9, 10, 11, or 12 bits, corresponding
to increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C,
respectively. The default resolution at power-up is 12 bits.
The device powers up in a low-power idle state. To initiate
aꢀtemperatureꢀmeasurementꢀandꢀA-to-Dꢀconversion,ꢀtheꢀ
masterꢀmustꢀissueꢀaꢀConvertꢀTꢀ[44h]ꢀcommand.ꢀFollowingꢀ
the conversion, the resulting thermal data is stored in the
2-byte temperature register in the scratchpad memory
and the device returns to its idle state.
A conventional surface-mount temperature sensor IC
has an excellent thermal connection to the circuit board
onꢀ whichꢀ itꢀ isꢀ mounted.ꢀ Heatꢀ travelsꢀ fromꢀ theꢀ boardꢀ
through the leads to the sensor die. Air temperature can
affect the die temperature, but the sensor’s package
does not conduct heat as well as the leads, so board
temperature has the greatest influence on the measured
temperature.
The device’s TO-92 package allows the sensor die to be
positioned above the board. The leads still conduct some
heat from the board, but because there is significant lead
area in contact with air, their temperature is also strongly
affectedꢀbyꢀairꢀtemperature.ꢀFollowꢀtheꢀguidelinesꢀbelowꢀtoꢀ
getꢀtheꢀbestꢀresultsꢀwhenꢀmeasuringꢀambientꢀtemperature:
The output temperature data is calibrated in degrees
Celsius;ꢀ forꢀ Fahrenheitꢀ applications,ꢀ aꢀ lookupꢀ tableꢀ orꢀ
conversion routine must be used. The temperature data
is stored as a 16-bit sign-extended two’s complement
number in the temperature register (see the Temperature
Register Format).ꢀTheꢀsignꢀbitsꢀ(S)ꢀindicateꢀifꢀtheꢀtempera-
tureꢀisꢀpositiveꢀorꢀnegative:ꢀforꢀpositiveꢀnumbersꢀSꢀ=ꢀ0ꢀandꢀ
forꢀnegativeꢀnumbersꢀSꢀ=ꢀ1.ꢀIfꢀtheꢀdeviceꢀisꢀconfiguredꢀ
for 12-bit resolution, all bits in the temperature register
containꢀvalidꢀdata.ꢀForꢀ11-bitꢀresolution,ꢀbitꢀ0ꢀisꢀundefined.ꢀ
Forꢀ10-bitꢀresolution,ꢀbitsꢀ1ꢀandꢀ0ꢀareꢀundefined,ꢀandꢀforꢀ
9-bit resolution bits 2, 1, and 0 are undefined. Table 1
gives examples of digital output data and the correspond-
ing temperature reading for 12-bit resolution conversions.
•
If air is moving (e.g., due to cooling fans), place the
sensor in the path of the air stream. This causes the
ambient temperature to influence the sensor tempera-
ture more strongly.
•
If the board contains components that will heat it, mount
the sensor as far as possible from those components.
This makes the temperature in the vicinity of the sensor
closer to the temperature of the ambient air.
•ꢀ PCBꢀ tracesꢀ andꢀ groundꢀ planesꢀ conductꢀ heatꢀ fromꢀ
Temperature Register Format
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
6
5
4
MSB
S
S
S
S
S
2
2
2
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
3
2
1
0
-1
2
-2
2
-3
2
-4
2
LSB
2
2
2
2
Table 1. Temperature/Data Relationship
TEMPERATURE (°C)
DIGITAL OUTPUT (BINARY)
0000 0101 0101 0000
0000 0001 1001 0001
0000 0000 1010 0010
0000 0000 0000 1000
0000 0000 0000 0000
1111 1111 1111 1000
1111 1111 0101 1110
1111 1110 0110 1111
1111 1100 1001 0000
DIGITAL OUTPUT (HEX)
+85*
+25.0625
+10.125
+0.5
0550h
0191h
00A2h
0008h
0000h
FFF8h
FF5Eh
FE6Fh
FC90h
0
-0.5
-10.125
-25.0625
-55
*The power-on-reset value of the temperature register is +85°C.
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Alarm Signaling
After the device performs a temperature conversion, the
temperature value is compared to the user-defined two’s
Parasite Power
The device’s parasite-power circuit allows it to operate
without a local power supply. Parasite power is very
useful for applications that require remote temperature
sensing, or those that are very space constrained.
Figureꢀ 1 shows the device’s parasite-power control
circuitry, which “steals” power from the 1-Wire bus
throughꢀ theꢀ DQꢀ pinꢀ whenꢀ theꢀ busꢀ isꢀ high.ꢀ Theꢀ stolenꢀ
charge powers the device while the bus is high, and
some of the charge is stored on the parasite-power
complement alarm trigger values stored in the 1-byte T
H
and T registers (see TH and TL Register Format). The
L
signꢀbitꢀ(S) indicatesꢀifꢀtheꢀvalueꢀisꢀpositiveꢀorꢀnegative;ꢀ
forꢀpositiveꢀnumbersꢀSꢀ=ꢀ0ꢀandꢀforꢀnegativeꢀnumbersꢀSꢀ
= 1. The T and T registers are nonvolatile (EEPROM)
H
L
so they retain data when the device is powered down.
T
and T can be accessed through bytes 2 and 3 of the
H
L
scratchpad, as explained in the Memory section.
capacitor (C ) to provide power when the bus is low.
PP
Onlyꢀbitsꢀ11:4ꢀofꢀtheꢀtemperatureꢀregisterꢀareꢀusedꢀinꢀtheꢀ
In parasite-power mode, the 1-Wire bus and C
can
PP
T and T comparison since T and T are 8-bit registers.
provide sufficient current to the device for most opera-
tions as long as the specified timing and voltage require-
ments are met (see the DC Electrical Characteristics and
AC Electrical Characteristics tables).ꢀHowever,ꢀwhenꢀtheꢀ
device is performing temperature conversions or copy-
ing data from the scratchpad memory to EEPROM, the
operating current can be as high as 1.5mA. This current
can cause an unacceptable voltage drop across the weak
1-Wire pullup resistor and is more current than can be
H
L
H
Lꢀ
If the measured temperature is lower than or equal to T
L
or higher than or equal to T , an alarm condition exists
H
and an alarm flag is set inside the device. This flag is
updatedꢀafterꢀeveryꢀtemperatureꢀmeasurement;ꢀtherefore,ꢀ
if the alarm condition goes away, the flag is turned off after
the next temperature conversion.
The master device can check the alarm flag status of all
MAX31820PAR devices on the bus by issuing an Alarm
Searchꢀ[ECh]ꢀcommand.ꢀAnyꢀdevicesꢀwithꢀaꢀsetꢀalarmꢀflagꢀ
respond to the command, so the master can determine
exactly which devices have experienced an alarm condi-
supplied by C . To ensure that the device has sufficient
PP
supply current, it is necessary to provide a strong pullup
on the 1-Wire bus whenever temperature conversions
are taking place, or data is being copied from the scratch-
pad to EEPROM. This can be accomplished by using a
MOSFETꢀ toꢀ pullꢀ theꢀ busꢀ directlyꢀ toꢀ theꢀ rail,ꢀ asꢀ shownꢀ
tion. If an alarm condition exists and the T or T settings
H
L
have changed, another temperature conversion should be
done to validate the alarm condition.
T and T Register Format
H
L
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
6
2
5
4
3
2
1
0
S
2
2
2
2
2
2
V
PU
MAX31820PAR
V
PU
GND DQ
µP
4.7kΩ
1-Wire BUS
TO OTHER 1-Wire DEVICES
Figure 1. Supplying the Parasite-Powered MAX31820PAR During Temperature Conversions
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
in Figureꢀ 1. The 1-Wire bus must be switched to the
strong pullup within 10µs (max) after a Convert T [44h] or
CopyꢀScratchpadꢀ[48h]ꢀcommandꢀisꢀissued,ꢀandꢀtheꢀbusꢀ
must be held high by the pullup for the duration of the
Memory
The device’s memory is organized as shown in
Figureꢀ3.ꢀTheꢀmemoryꢀconsistsꢀofꢀanꢀSRAMꢀscratchpadꢀwithꢀ
nonvolatile EEPROM storage for the high and low alarm
trigger registers (T and T ) and configuration register.
Noteꢀthatꢀifꢀtheꢀdeviceꢀalarmꢀfunctionꢀisꢀnotꢀused,ꢀtheꢀT
conversion (t
) or data transfer (t
ꢀ =ꢀ 10ms).ꢀ Noꢀ
CONV
WR
H
L
other activity can take place on the 1-Wire bus while the
pullup is enabled.
H
and T registers can serve as general-purpose memory.
L
All memory commands are described in detail in the
MAX31820PAR Function Commands section.
64-Bit Lasered ROM Code
Each device contains a unique 64-bit code stored in
ROM (Figureꢀ2). 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.
Byteꢀ0ꢀandꢀbyteꢀ1ꢀofꢀtheꢀscratchpadꢀcontainꢀtheꢀLSBꢀandꢀ
theꢀMSBꢀofꢀtheꢀtemperatureꢀregister,ꢀrespectively.ꢀTheseꢀ
bytesꢀareꢀread-only.ꢀBytesꢀ2ꢀandꢀ3ꢀprovideꢀaccessꢀtoꢀT
H
and T ꢀregisters.ꢀByteꢀ4ꢀcontainsꢀtheꢀconfigurationꢀregis-
L
ter data, which is explained in detail in the Configuration
Registerꢀsection.ꢀBytesꢀ7:5ꢀareꢀreservedꢀforꢀinternalꢀuseꢀbyꢀ
theꢀdeviceꢀandꢀcannotꢀbeꢀoverwritten.ꢀByteꢀ8ꢀofꢀtheꢀscratch-
padꢀisꢀread-onlyꢀandꢀcontainsꢀtheꢀCRCꢀcodeꢀforꢀbytesꢀ7:0ꢀ
of the scratchpad. The device generates this CRC using
the method described in the CRC Generation section.
MSb
LSb
8-BIT
CRC CODE
8-BIT FAMILY CODE
(28h)
48-BIT SERIAL NUMBER
MSb
LSb MSb
LSb MSb
LSb
Figure 2. 64-Bit Lasered ROM Code
SCRATCHPAD (POWER-UP STATE
SHOWN IN PARENTHESES)
BYTE 0
TEMPERATURE REGISTER LSB (50h)
BYTE 1 TEMPERATURE REGISTER MSB (05h)
EEPROM
T REGISTER OR USER BYTE 1
H
BYTE 2
BYTE 3
BYTE 4
BYTE 5
BYTE 6
BYTE 7
BYTE 8
T
REGISTER OR USER BYTE 1*
H
T REGISTER OR USER BYTE 2*
L
T REGISTER OR USER BYTE 2
L
CONFIGURATION REGISTER*
RESERVED (FFh)
RESERVED
CONFIGURATION REGISTER
RESERVED (10h)
CRC*
*POWER-UP STATE DEPENDS ON VALUE(S) STORED IN EEPROM.
Figure 3. Memory Map
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Dataꢀisꢀwrittenꢀtoꢀbytesꢀ4:2ꢀofꢀtheꢀscratchpadꢀusingꢀtheꢀ
Writeꢀ Scratchpadꢀ [4Eh]ꢀ command;ꢀ theꢀ dataꢀ mustꢀ beꢀ
transmitted to the device starting with the least significant
bit of byte 2. To verify data integrity, the scratchpad can
beꢀ readꢀ (usingꢀ theꢀ Readꢀ Scratchpadꢀ [BEh]ꢀ command)ꢀ
after the data is written. When reading the scratchpad,
data is transferred over the 1-Wire bus starting with the
master can issue read time slots following the Recall
E 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.
2
Configuration Register
Byteꢀ4ꢀofꢀtheꢀscratchpadꢀmemoryꢀcontainsꢀtheꢀconfigura-
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
R0ꢀ=ꢀ1ꢀandꢀR1ꢀ=ꢀ1ꢀ(12-bitꢀresolution).ꢀNoteꢀthatꢀthereꢀisꢀ
a direct trade-off between resolution and conversion time.
Bitꢀ7ꢀandꢀbitsꢀ4:0ꢀinꢀtheꢀconfigurationꢀregisterꢀareꢀreservedꢀ
for internal use by the device and cannot be overwritten.
least significant bit of byte 0. To transfer the T , T , and
H
L
configuration data from the scratchpad to EEPROM, the
masterꢀmustꢀissueꢀtheꢀCopyꢀScratchpadꢀ[48h]ꢀcommand.ꢀ
Dataꢀ inꢀ theꢀ EEPROMꢀ registersꢀ isꢀ retainedꢀ whenꢀ theꢀ
deviceꢀisꢀpoweredꢀdown;ꢀatꢀpower-upꢀtheꢀEEPROMꢀdataꢀ
is reloaded into the corresponding scratchpad locations.
DataꢀcanꢀalsoꢀbeꢀreloadedꢀfromꢀEEPROMꢀtoꢀtheꢀscratch-
2
pad at any time using the Recall E ꢀ[B8h]ꢀcommand.ꢀTheꢀ
Configuration Register Format
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
R1
R0
1
1
1
1
1
Table 2. Thermometer Resolution Configuration
R1
0
R0
0
RESOLUTION (BITS)
MAX CONVERSION TIME
9
93.75ms
187.5ms
375ms
(t
(t
(t
/8)
CONV
CONV
CONV
0
1
10
11
12
/4)
/2)
1
0
1
1
750ms
(t
)
CONV
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
8
5
4
POLYNOMIAL = X + X + X + 1
1ST
STAGE
2ND
STAGE
3RD
STAGE
4TH
STAGE
5TH
STAGE
6TH
STAGE
7TH
STAGE
8TH
STAGE
0
1
2
3
4
5
6
7
8
X
X
X
X
X
X
X
X
X
INPUT DATA
Figure 4. CRC Generator
The equivalent polynomial function of the CRC (ROM or
scratchpad)ꢀis:
CRC Generation
CRC bytes are provided as part of the device’s 64-bit
ROM code and in the 9th byte of the scratchpad memory.
The ROM code CRC is calculated from the first 56 bits
of the ROM code and is contained in the most significant
byte of the ROM. The scratchpad CRC is calculated from
the data stored in the scratchpad, and therefore changes
when the data in the scratchpad changes. The CRCs
provide the bus master with a method of data validation
when data is read from the device. To verify that data has
been read correctly, the bus master must recalculate the
CRC from the received data and then compare this value
to either the ROM code CRC (for ROM reads) or to the
scratchpad CRC (for scratchpad reads). If the calculated
CRC matches the read CRC, the data has been received
error free. The comparison of CRC values and the
decision to continue with an operation are determined
entirely by the bus master. There is no circuitry inside
the device that prevents a command sequence from pro-
ceeding if the device CRC (ROM or scratchpad) does not
match the value generated by the bus master.
8
5
4
CRC = X + X + X + 1
The bus master can recalculate the CRC and compare
it to the CRC values from the MAX31820PAR using the
polynomial generator shown in Figureꢀ 4. This circuit
consists of a shift register and XOR gates, and the shift
registerꢀ bitsꢀ areꢀ initializedꢀ toꢀ 0.ꢀ Startingꢀ withꢀ theꢀ leastꢀ
significant bit of the ROM code or the least significant bit
of byte 0 in the scratchpad, one bit at a time should be
shifted into the shift register. After shifting in the 56th bit
fromꢀtheꢀROMꢀorꢀtheꢀmostꢀsignificantꢀbitꢀofꢀbyteꢀ7ꢀfromꢀ
the scratchpad, the polynomial generator contains the
recalculatedꢀCRC.ꢀNext,ꢀtheꢀ8-bitꢀROMꢀcodeꢀorꢀscratch-
pad CRC from the device must be shifted into the circuit.
At this point, if the recalculated CRC was correct, the shift
register contains all 0s. Additional information about the
Maxim Integrated 1-Wire CRC is available in Application
Noteꢀ 27: Understanding and Using Cyclic Redundancy
Checks with Maxim iButton® Products.
iButton is a registered trademark of Maxim Integrated
Products, Inc.
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
V
PU
V
PU
MAX31820PAR 1-Wire PORT
STRONG
PULLUP
4.7kΩ
DQ
1-Wire BUS PIN
R
T
R
X
X
5µA
TYP
T
X
X
100Ω
MOSFET
R
X
= RECEIVE
T
= TRANSMIT
X
MICROPROCESSOR
Figure 5. Hardware Configuration
has sufficient supply current during temperature conver-
sions, it is necessary to provide a strong pullup (such as
aꢀ MOSFET)ꢀ onꢀ theꢀ 1-Wireꢀ busꢀ wheneverꢀ temperatureꢀ
conversions or EEPROM writes are taking place (as
described in the Parasite Power section.
1-Wire Bus System
The 1-Wire bus system uses a single bus master to con-
trol one or more slave devices. The MAX31820PAR is
always a slave. When there is only one slave on the bus,
theꢀsystemꢀisꢀreferredꢀtoꢀasꢀaꢀsingle-dropꢀsystem;ꢀtheꢀsys-
tem is multidrop if there are multiple slaves on the bus. All
data and commands are transmitted least significant bit
first over the 1-Wire bus.
Transaction Sequence
The transaction sequence for accessing the device is as
follows:
The following discussion of the 1-Wire bus system is
brokenꢀ downꢀ intoꢀ threeꢀ topics:ꢀ hardwareꢀ configuration,ꢀ
transaction sequence, and 1-Wire signaling (signal types
and timing).
1)ꢀ Stepꢀ1:ꢀInitialization
2)ꢀ Stepꢀ2:ꢀROMꢀcommandꢀ(followedꢀbyꢀanyꢀrequiredꢀdataꢀ
exchange)
3)ꢀ Stepꢀ3:ꢀMAX31820PARꢀFunctionꢀcommandꢀ(followedꢀ
Hardware Configuration
by any required data exchange)
The 1-Wire bus has, by definition, only a single data line.
Each device (master or slave) interfaces to the data line
through an open-drain or three-state port. This allows
each device to release the data line when the device is
not transmitting data so the bus is available for use by
another device. The 1-Wire port of the MAX31820PAR
(theꢀDQꢀpin)ꢀisꢀopenꢀdrainꢀwithꢀanꢀinternalꢀcircuitꢀequiva-
lent to that shown in Figureꢀ5.
It is very important to follow this sequence every time
the device is accessed, as the device does not respond
if any steps in the sequence are missing or out of order.
Exceptionsꢀ toꢀ thisꢀ ruleꢀ areꢀ theꢀ Searchꢀ ROMꢀ [F0h]ꢀ andꢀ
Alarmꢀ Searchꢀ [ECh]ꢀ commands.ꢀ Afterꢀ issuingꢀ eitherꢀ ofꢀ
theseꢀROMꢀcommands,ꢀtheꢀmasterꢀmustꢀreturnꢀtoꢀStepꢀ1ꢀ
in the sequence.
Initialization
The 1-Wire bus requires an external pullup resis-
torꢀ ofꢀ approximatelyꢀ 5kΩ;ꢀ thus,ꢀ theꢀ idleꢀ stateꢀ forꢀ theꢀ
1-Wire bus is high. If for any reason a transaction needs
to be suspended, the bus must be left in the idle state if
the transaction is to resume. Infinite recovery time can
occur between bits so long as the 1-Wire bus is in the
inactive (high) state during the recovery period. If the bus
is held low for more than 480µs, all components on the
bus will be reset. Additionally, to ensure that the device
All transactions on the 1-Wire bus begin with an initializa-
tion sequence. The initialization sequence consists of a
reset pulse transmitted by the bus master, followed by
presence pulse(s) transmitted by the slave(s). The pres-
ence pulse lets the bus master know that slave devices
(such as the MAX31820PAR) are on the bus and are
ready to operate. Timing for the reset and presence
pulses is detailed in the 1-Wire Signaling section.
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Match ROM [55h]
ROM Commands
The match ROM command, followed by a 64-bit ROM
code sequence, allows the bus master to address a
specific slave device on a multidrop or single-drop bus.
Only the slave that exactly matches the 64-bit ROM code
sequence responds to the function command issued by
theꢀ master;ꢀ allꢀ otherꢀ slavesꢀ onꢀ theꢀ busꢀ waitꢀ forꢀ aꢀ resetꢀ
pulse.
After the bus master has detected a presence pulse, it
can issue a ROM command. These commands operate
on the unique 64-bit ROM codes of each slave device
and allow the master to single out a specific device if
many are present on the 1-Wire bus. These commands
also allow the master to determine how many and what
types of devices are present on the bus or if any device
has experienced an alarm condition. There are five ROM
commands, and each command is 8 bits long. The master
device must issue an appropriate ROM command before
issuingꢀ aꢀ MAX31820PARꢀ Functionꢀ command.ꢀ Figureꢀ 6
shows a flowchart for operation of the ROM commands.
Skip ROM [CCh]
The master can use this command to address all devices
on the bus simultaneously, without sending out any ROM
codeꢀinformation.ꢀForꢀexample,ꢀtheꢀmasterꢀcanꢀmakeꢀallꢀ
devices on the bus perform simultaneous temperature
conversionsꢀ byꢀissuingꢀ aꢀSkipꢀ ROMꢀcommandꢀ followedꢀ
by a Convert T [44h] command.
Search ROM [F0h]
When a system is initially powered up, the master must
identify the ROM codes of all slave devices on the bus,
which allows the master to determine the number of
slaves and their device types. The master learns the ROM
codes through a process of elimination that requires the
masterꢀtoꢀperformꢀaꢀSearchꢀROMꢀcycleꢀ(i.e.,ꢀSearchꢀROMꢀ
command followed by data exchange) as many times as
necessary to identify all the slave devices. If there is only
one slave on the bus, the simpler Read ROM command
canꢀbeꢀusedꢀinꢀplaceꢀofꢀtheꢀSearchꢀROMꢀprocess.ꢀForꢀaꢀ
detailedꢀexplanationꢀofꢀtheꢀSearchꢀROMꢀprocedure,ꢀreferꢀ
to ApplicationꢀNoteꢀ937:ꢀBook of iButton Standards. After
everyꢀSearchꢀROMꢀcycle,ꢀtheꢀbusꢀmasterꢀmustꢀreturnꢀtoꢀ
Stepꢀ1ꢀ(initialization)ꢀinꢀtheꢀtransactionꢀsequence.
Noteꢀ thatꢀ theꢀ Readꢀ Scratchpadꢀ [BEh]ꢀ commandꢀ canꢀ
followꢀ theꢀSkipꢀROMꢀcommandꢀ onlyꢀifꢀthereꢀisꢀaꢀsingleꢀ
slave device on the bus. In this case, time is saved by
allowing the master to read from the slave without send-
ingꢀtheꢀdevice’sꢀ64-bitꢀROMꢀcode.ꢀAꢀSkipꢀROMꢀcommandꢀ
followedꢀbyꢀaꢀReadꢀScratchpadꢀcommandꢀcausesꢀaꢀdataꢀ
collision on the bus if there is more than one slave since
multiple devices attempt to transmit data simultaneously.
Alarm Search [ECh]
The operation of this command is identical to the opera-
tionꢀofꢀtheꢀSearchꢀROMꢀcommandꢀexceptꢀthatꢀonlyꢀslavesꢀ
with a set alarm flag respond. This command allows
the master device to determine if any MAX31820PARs
experienced an alarm condition during the most recent
temperatureꢀconversion.ꢀAfterꢀeveryꢀAlarmꢀSearchꢀcycleꢀ
(i.e.,ꢀAlarmꢀSearchꢀcommandꢀfollowedꢀbyꢀdataꢀexchange),ꢀ
theꢀbusꢀmasterꢀmustꢀreturnꢀtoꢀStepꢀ1ꢀ(initialization)ꢀinꢀtheꢀ
transactionꢀ sequence.ꢀ Seeꢀ theꢀ Alarm Signaling section
for an explanation of alarm flag operation.
Read ROM [33h]
This command can only be used when there is one slave
on the bus. It allows the bus master to read the slave’s
64-bitꢀROMꢀcodeꢀwithoutꢀusingꢀtheꢀSearchꢀROMꢀproce-
dure. If this command is used when there is more than
one slave present on the bus, a data collision occurs
when all the slaves attempt to respond at the same time.
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
MASTER T
X
RESET PULSE
INITIALIZATION
SEQUENCE
DEVICE T
X
PRESENCE PULSE
MASTER T
X
ROM COMMAND
33h
READ
ROM?
55h
MATCH
ROM?
F0h
SEARCH
ROM?
ECh
CCh
SKIP
ROM?
N
N
N
N
N
ALARM SEARCH
COMMAND
Y
Y
Y
Y
Y
DEVICE T BIT 0
DEVICE T BIT
X
X
MASTER T
BIT 0
X
DEVICE T BIT 0
DEVICE T BIT
X
X
MASTER T BIT 0
X
MASTER T BIT 0
X
DEVICE(S)
WITH ALARM
FLAG SET?
N
N
BIT 0
MATCH?
BIT 0
MATCH?
N
Y
Y
Y
DEVICE T
FAMILY CODE
1 BYTE
X
DEVICE T BIT 1
X
MASTER T
BIT 1
X
DEVICE T BIT 1
X
MASTER T BIT 1
X
DEVICE T
X
SERIAL NUMBER
6 BYTES
BIT 1
MATCH?
BIT 1
MATCH?
N
N
DEVICE T
CRC BYTE
X
Y
Y
DEVICE T BIT 63
X
MASTER T
BIT 63
X
DEVICE T BIT 63
X
MASTER T BIT 63
X
N
N
BIT 63
BIT 63
MATCH?
MATCH?
Y
Y
MASTER T
X
FUNCTION COMMAND
Figure 6. ROM Commands Flowchart
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
bytes must be written before the master issues a reset,
or the data may be corrupted.
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 Figureꢀ7 illustrates the function
commands.
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]
Convert T [44h]
This command copies the contents of the scratchpad
This command initiates a single temperature conversion.
Followingꢀ theꢀ conversion,ꢀ theꢀ resultingꢀ thermalꢀ dataꢀ isꢀ
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
T , T and configuration registers (bytes 2, 3, and 4)
H
L
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.
2
Recall E [B8h]
the duration of the conversion (t
), as described in
CONV
the Parasite Power section.
This command recalls the alarm trigger values (T and
H
T ) and configuration data from EEPROM and places the
L
Write Scratchpad [4Eh]
data in bytes 2, 3, and 4, respectively, in the scratchpad
memory. The master device can issue read time slots fol-
This command allows the master to write 3 bytes of data
to the device’s scratchpad. The first data byte is written
2
lowing the Recall E command and the device indicates
into the T register (byte 2 of the scratchpad), the second
H
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.
byte is written into the T register (byte 3), and the third
L
byteꢀisꢀwrittenꢀintoꢀtheꢀconfigurationꢀregisterꢀ(byteꢀ4).ꢀDataꢀ
must be transmitted least significant bit first. All three
Table 3. MAX31820PAR Function Command Set
1-Wire BUS ACTIVITY AFTER COMMAND IS
COMMAND
DESCRIPTION
PROTOCOL
ISSUED
Convert T
(Noteꢀ1)
Initiates temperature conversion.
44h
None.
ReadꢀScratchpad
(Noteꢀ2)
Reads the entire scratchpad
including the CRC byte.
BEh
The device transmits up to 9 data bytes to master.
The master transmits 3 data bytes to the device.
Writes to scratchpad bytes 2, 3,
WriteꢀScratchpadꢀ
(Noteꢀ3)
and 4 (T , T ,ꢀandꢀconfigurationꢀ
4Eh
48h
B8h
H
L
registers).
Copies T , T ,ꢀandꢀconfigurationꢀ
H
L
CopyꢀScratchpadꢀ
(Noteꢀ1)
register data from the scratchpad to
EEPROM.
None.
Recalls T , T ,ꢀandꢀconfigurationꢀ
H
L
2
Recall E
register data from EEPROM to the
The device transmits recall status to the master.
scratchpad.
Note 1: The master must enable a strong pullup on the 1-Wire bus during temperature conversions and copies from the scratchpad
toꢀEEPROM.ꢀNoꢀotherꢀbusꢀactivityꢀcanꢀtakeꢀplaceꢀduringꢀthisꢀtime.
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.
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
48h
COPY
SCRATCHPAD?
44h
CONVERT
T?
N
N
MASTER T
X
FUNCTION COMMAND
Y
Y
MASTER ENABLES
MASTER ENABLES
STRONG PULLUP ON DQ
STRONG PULLUP ON DQ
DEVICE CONVERTS
TEMPERATURE
DATA COPIED FROM
SCRATCHPAD TO EEPROM
MASTER DISABLES
STRONG PULLUP
MASTER DISABLES
STRONG PULLUP
BEh
READ
SCRATCHPAD
?
4Eh
WRITE
SCRATCHPAD
?
B8h
RECALL E
?
N
N
N
2
Y
Y
Y
MASTER T
T BYTE
H
X
TO SCRATCHPAD
MASTER T T BYTE
TO SCRATCHPAD
X
L
MASTER BEGINS DATA
RECALL FROM E PROM
MASTER R DATA BYTE
X
FROM SCRATCHPAD
2
MASTER T CONFIG.
X
BYTE TO SCRATCHPAD
MASTER T
RESET?
Y
X
N
DEVICE
BUSY RECALLING
N
DATA
?
N
HAVE 8 BYTES
BEEN READ?
Y
MASTER R
“0s”
MASTER R
X
X
Y
“1s”
MASTER R SCRATCHPAD
X
CRC BYTE
RETURN TO INITIALIZATION SEQUENCE
FOR NEXT TRANSACTION
Figure 7. MAX31820PAR Function Commands Flowchart
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
as illustrated in Figureꢀ 8. When the device sends the
presence pulse in response to the reset, it is indicating to
the master that it is on the bus and ready to operate.
1-Wire Signaling
The MAX31820PAR uses a strict 1-Wire communication
protocolꢀtoꢀensureꢀdataꢀintegrity.ꢀSeveralꢀsignalꢀtypesꢀareꢀ
definedꢀbyꢀthisꢀprotocol:ꢀresetꢀpulse,ꢀpresenceꢀpulse,ꢀwriteꢀ
0, write 1, read 0, and read 1. The bus master initiates all
these signals, with the exception of the presence pulse.
Duringꢀ theꢀ initializationꢀ sequence,ꢀ theꢀ busꢀ masterꢀ
transmits (T ) the reset pulse by pulling the 1-Wire bus
X
low for a minimum of 480µs. The bus master then releas-
es the bus and goes into receive mode (R ). When the
X
Initialization Procedure: Reset and Presence
Pulses
All communication with the device begins with an initial-
ization sequence that consists of a reset pulse from the
master followed by a presence pulse from the device,
busꢀisꢀreleased,ꢀtheꢀ5kΩꢀpullupꢀresistorꢀpullsꢀtheꢀ1-Wireꢀ
bus high. When the device detects this rising edge, it
waits 15µs to 60µs and then transmits a presence pulse
by pulling the 1-Wire bus low for 60µs to 240µs.
MASTER T RESET PULSE
X
MASTER R
X
480µs MINIMUM
480µs MINIMUM
DEVICE T PRESENCE PULSE
X
DEVICE WAITS
15µs TO 60µs
60µs TO 240µs
V
PU
1-Wire BUS
GND
BUS MASTER PULLING LOW
DEVICE PULLING LOW
RESISTOR PULLUP
Figure 8. Initialization Timing
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
slots.ꢀ Bothꢀ typesꢀ ofꢀ writeꢀ timeꢀ slotsꢀ areꢀ initiatedꢀ byꢀ theꢀ
master pulling the 1-Wire bus low (Figureꢀ9).
Read/Write Time Slots
The bus master writes data to the device during write time
slots and reads data from the device during read time
slots. One bit of data is transmitted over the 1-Wire bus
per time slot.
To generate a write-one time slot, after pulling the 1-Wire
bus low, the bus master must release the 1-Wire bus
withinꢀ 15µs.ꢀ Whenꢀ theꢀ busꢀ isꢀ released,ꢀ theꢀ 5kΩꢀ pullupꢀ
resistor pulls the bus high. To generate a write-zero time
slot, after pulling the 1-Wire bus low, the bus master must
continue to hold the bus low for the duration of the time
slot (at least 60µs).
Write Time Slots
Thereꢀ areꢀ twoꢀ typesꢀ ofꢀ writeꢀ timeꢀ slots:ꢀ write-oneꢀ timeꢀ
slots and write-zero time slots. The bus master uses a
write-one time slot to write a logic 1 to the device and a
write-zero time slot to write a logic 0 to the device. All write
time slots must be a minimum of 60µs in duration with a
minimum of a 1µs recovery time between individual write
The device samples the 1-Wire bus during a window that lasts
from 15µs to 60µs after the master initiates the write time slot.
If the bus is high during the sampling window, a 1 is written to
the device. If the line is low, a 0 is written to the device.
START
START
OF SLOT
OF SLOT
MASTER WRITE-ZERO SLOT
MASTER WRITE-ONE SLOT
1µs < t
< ∞
REC
60µs < T “0” < 120µs
X
> 1µs
V
PU
1-Wire BUS
GND
DEVICE SAMPLES
TYP
DEVICE SAMPLES
TYP
MIN
MAX
MIN
MAX
15µs
15µs
30µs
15µs
15µs
30µs
MASTER READ-ZERO SLOT
MASTER READ-ONE SLOT
1µs < t
< ∞
REC
V
PU
1-Wire BUS
GND
MASTER SAMPLES
> 1µs
MASTER SAMPLES
> 1µs
15µs
45µs
15µs
BUS MASTER PULLING LOW
DEVICE PULLING LOW
RESISTOR PULLUP
Figure 9. Read/Write Time Slot Timing Diagram
Maxim Integrated
│ 17
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
The device transmits a 1 by leaving the bus high and
transmits a 0 by pulling the bus low. When transmitting
a 0, the device releases the bus by the end of the time
slot, and the bus is pulled back to its high idle state by
the pullup resister. Output data from the device is valid
for 15µs after the falling edge that initiated the read time
slot. Therefore, the master must release the bus and then
sample the bus state within 15µs from the start of the slot.
Read Time Slots
The device can only transmit data to the master when
the master issues read time slots. Therefore, the master
must generate read time slots immediately after issuing
aꢀ Readꢀ Scratchpadꢀ [BEh]ꢀ command,ꢀ soꢀ thatꢀ theꢀ deviceꢀ
can provide the requested data. In addition, the master
2
can generate read time slots after issuing a Recall E
[B8h]ꢀcommandꢀtoꢀfindꢀoutꢀtheꢀstatusꢀofꢀtheꢀoperation,ꢀasꢀ
explained in the Parasite Power section.
Figureꢀ 10 illustrates that the sum of t , t , and
INIT RC
t
must be less than 15µs for a read time slot.
SAMPLE
All read time slots must be a minimum of 60µs in duration
with a minimum of a 1µs recovery time between slots. A
read time slot is initiated by the master device pulling the
1-Wire bus low for a minimum of 1µs and then releasing
the bus (Figureꢀ9). After the master initiates the read time
slot, the device begins transmitting a 1 or 0 on the bus.
Figureꢀ11 shows that system timing margin is maximized
by keeping t and t as short as possible and by
locating the master sample time during read time slots
INIT
RC
towards the end of the 15µs period.
V
PU
V
IH
OF MASTER
1-Wire BUS
GND
t
> 1µs
t
MASTER SAMPLES
INIT
RC
15µs
BUS MASTER PULLING LOW
RESISTOR PULLUP
Figure 10. Detailed Master Read-One Timing
V
PU
V
IH
OF MASTER
1-Wire BUS
GND
MASTER SAMPLES
t
=
t
=
RC
INIT
SMALL SMALL
15µs
BUS MASTER PULLING LOW
RESISTOR PULLUP
Figure 11. Recommended Master Read-One Timing
Maxim Integrated
│ 18
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Example 2
Operation Examples
In Table 5 there is only one device on the bus. The
master writes to the T , T , 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.
Example 1
H
L
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.
Table 4. Operation Example 1
MASTER
MODE
DATA
(LSB FIRST)
COMMENTS
Tx
Rx
Tx
Tx
Tx
Reset
Presence
55h
Master issues reset pulse.
Devicesꢀrespondꢀwithꢀpresenceꢀpulse.
Master issues Match ROM command.
Master sends device ROM code.
Master issues Convert T command.
64-bit ROM code
44h
DQꢀlineꢀheldꢀhighꢀbyꢀ
Tx
MasterꢀappliesꢀstrongꢀpullupꢀtoꢀDQꢀforꢀtheꢀdurationꢀofꢀtheꢀconversionꢀ(t
).
CONV
strong pullup
Tx
Rx
Tx
Tx
Tx
Reset
Presence
55h
Master issues reset pulse.
Devicesꢀrespondꢀwithꢀpresenceꢀpulse.
Master issues Match ROM command.
Master sends device ROM code.
MasterꢀissuesꢀReadꢀScratchpadꢀcommand.
64-bit ROM code
BEh
Master reads entire scratchpad including CRC. The master then recalculates the CRC of the
firstꢀ8ꢀdataꢀbytesꢀfromꢀtheꢀscratchpadꢀandꢀcomparesꢀtheꢀcalculatedꢀCRCꢀwithꢀtheꢀreadꢀCRCꢀ
(byteꢀ9).ꢀIfꢀtheyꢀmatch,ꢀtheꢀmasterꢀcontinues;ꢀifꢀnot,ꢀtheꢀreadꢀoperationꢀisꢀrepeated.
Rx
9 data bytes
Table 5. Operation Example 2
MASTER
MODE
DATA
(LSB FIRST)
COMMENTS
Tx
Rx
Tx
Tx
Tx
Tx
Rx
Tx
Tx
Reset
Presence
CCh
Master issues reset pulse.
Deviceꢀrespondsꢀwithꢀpresenceꢀpulse.
MasterꢀissuesꢀSkipꢀROMꢀcommand.ꢀ
4Eh
MasterꢀissuesꢀWriteꢀScratchpadꢀcommand.
Master sends 3 data bytes to the scratchpad (T , T ,ꢀandꢀconfigurationꢀregisters).
3 data bytes
Reset
H
L
Master issues reset pulse.
Presence
CCh
Deviceꢀrespondsꢀwithꢀpresenceꢀpulse.
MasterꢀissuesꢀSkipꢀROMꢀcommand.
MasterꢀissuesꢀReadꢀScratchpadꢀcommand.
BEh
Master reads entire scratchpad including CRC. The master then recalculates the CRC of the
firstꢀ8ꢀdataꢀbytesꢀfromꢀtheꢀscratchpadꢀandꢀcomparesꢀtheꢀcalculatedꢀCRCꢀwithꢀtheꢀreadꢀCRCꢀ
(byteꢀ9).ꢀIfꢀtheyꢀmatch,ꢀtheꢀmasterꢀcontinues;ꢀifꢀnot,ꢀtheꢀreadꢀoperationꢀisꢀrepeated.
Rx
9 data bytes
Tx
Rx
Tx
Tx
Reset
Presence
CCh
Master issues reset pulse.
Deviceꢀrespondsꢀwithꢀpresenceꢀpulse.
MasterꢀissuesꢀSkipꢀROMꢀcommand.
MasterꢀissuesꢀCopyꢀScratchpadꢀcommand.
48h
DQꢀlineꢀheldꢀhighꢀbyꢀ
Tx
MasterꢀappliesꢀstrongꢀpullupꢀtoꢀDQꢀforꢀatꢀleastꢀ10msꢀwhileꢀcopyꢀoperationꢀisꢀinꢀprogress.
strong pullup
Maxim Integrated
│ 19
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Ordering Information
PART
TEMP RANGE
-55°C to +125°C
-55°C to +125°C
PIN-PACKAGE
MAX31820PARMCR+
MAX31820PARMCR+T
3 TO-92 (straight leads)
3 TO-92 (formed leads)
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Package Information
Forꢀtheꢀlatestꢀpackageꢀoutlineꢀinformationꢀandꢀlandꢀpatternsꢀ(footprints),ꢀgoꢀto www.maximintegrated.com/packages.ꢀNoteꢀthatꢀaꢀ“+”,ꢀ
“#”,ꢀorꢀ“-”ꢀinꢀtheꢀpackageꢀcodeꢀindicatesꢀRoHSꢀstatusꢀonly.ꢀPackageꢀdrawingsꢀmayꢀshowꢀaꢀdifferentꢀsuffixꢀcharacter,ꢀbutꢀtheꢀdrawingꢀ
pertainsꢀtoꢀtheꢀpackageꢀregardlessꢀofꢀRoHSꢀstatus.
PACKAGE TYPE
3 TO-92 (straight leads)
3 TO-92 (formed leads)
PACKAGE CODE
Q3+1
OUTLINE NO.
21-0248
LAND PATTERN NO.
—
—
Q3+4
21-0250
Maxim Integrated
│ 20
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MAX31820PAR
1-Wire, Parasite-Power,
Ambient Temperature Sensor
Revision History
REVISION REVISION
PAGES
CHANGED
DESCRIPTION
NUMBER
DATE
0
6/13
Initial release
—
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
©
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
2013 Maxim Integrated Products, Inc.
│ 21
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