DS18B20U+T&R - Maxim Integrated - Datasheet.Directory

General Description

The DS18B20 digital thermometer provides 9-bit to

12-bit Celsius temperature measurements and has an

alarm function with nonvolatile user-programmable upper

and lower trigger points. The DS18B20 communicates

over a 1-Wire bus that by definition requires only one

data line (and ground) for communication with a central

microprocessor. In addition, the DS18B20 can derive

power directly from the data line (“parasite power”),

eliminating the need for an external power supply.

Each DS18B20 has a unique 64-bit serial code, which

allows multiple DS18B20s to function on the same 1-Wire

bus. Thus, it is simple to use one microprocessor to

control many DS18B20s distributed over a large area.

Applications that can benefit from this feature include

HVAC environmental controls, temperature monitoring

systems inside buildings, equipment, or machinery, and

process monitoring and control systems.

Applications

●Thermostatic Controls

●Industrial Systems

●Consumer Products

●Thermometers

●Thermally Sensitive Systems

Benets and Features

●Unique 1-Wire® Interface Requires Only One Port

Pin for Communication

●Reduce Component Count with Integrated

Temperature Sensor and EEPROM

• Measures Temperatures from -55°C to +125°C

(-67°F to +257°F)

• ±0.5°C Accuracy from -10°C to +85°C

• Programmable Resolution from 9 Bits to 12 Bits

• No External Components Required

●Parasitic Power Mode Requires Only 2 Pins for

Operation (DQ and GND)

●Simplifies Distributed Temperature-Sensing

Applications with Multidrop Capability

• Each Device Has a Unique 64-Bit Serial Code

Stored in On-Board ROM

●Flexible User-Definable Nonvolatile (NV) Alarm Settings

with Alarm Search Command Identifies Devices with

Temperatures Outside Programmed Limits

●Available in 8-Pin SO (150 mils), 8-Pin µSOP, and

3-Pin TO-92 Packages

19-7487; Rev 5; 9/18

Ordering Information appears at end of data sheet.

1-Wire is a registered trademark of Maxim Integrated Products, Inc.

Pin Congurations

BOTTOM VIEW

N.C.

VDD

N.C.

GND

DS18B20

SO (150 mils)

(DS18B20Z)

N.C.

GND

N.C.

DS18B20

µSOP

(DS18B20U)

DS18B20

1 2 3

GND DQ V

1 2 3

TOP VIEW

TO-92

(DS18B20)

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

Click here for production status of specific part numbers.

Voltage Range on Any Pin Relative to Ground ....-0.5V to +6.0V

Operating Temperature Range ......................... -55°C to +125°C

Storage Temperature Range ............................ -55°C to +125°C

Solder Temperature ............................... Refer to the IPC/JEDEC

J-STD-020 Specification.

(-55°C to +125°C; VDD = 3.0V to 5.5V)

Note 1: All voltages are referenced to ground.

Note 2: The Pullup Supply Voltage specification assumes that the pullup device is ideal, and therefore the high level of the

pullup is equal to VPU. In order to meet the VIH spec of the DS18B20, the actual supply rail for the strong pullup transis-

tor must include margin for the voltage drop across the transistor when it is turned on; thus: VPU_ACTUAL = VPU_IDEAL +

VTRANSISTOR.

Note 3: See typical performance curve in Figure 1. Thermometer Error limits are 3-sigma values.

Note 4: Logic-low voltages are specified at a sink current of 4mA.

Note 5: To guarantee a presence pulse under low voltage parasite power conditions, VILMAX may have to be reduced to as low as

0.5V.

Note 6: Logic-high voltages are specified at a source current of 1mA.

Note 7: Standby current specified up to +70°C. Standby current typically is 3µA at +125°C.

Note 8: To minimize IDDS, DQ should be within the following ranges: GND ≤ DQ ≤ GND + 0.3V or VDD – 0.3V ≤ DQ ≤ VDD.

Note 9: Active current refers to supply current during active temperature conversions or EEPROM writes.

Note 10: DQ line is high (“high-Z” state).

Note 11: Drift data is based on a 1000-hour stress test at +125°C with VDD = 5.5V.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VDD Local power (Note 1) +3.0 +5.5 V

Pullup Supply Voltage VPU

Parasite power (Notes 1, 2) +3.0 +5.5 V

Local power +3.0 VDD

Thermometer Error tERR

-10°C to +85°C

(Note 3)

±0.5

°C

-30°C to +100°C ±1

-55°C to +125°C ±2

Input Logic-Low VIL (Notes 1, 4, 5) -0.3 +0.8 V

Input Logic-High VIH

Local power

(Notes 1,6)

+2.2 The lower

of 5.5 or

VDD + 0.3

Parasite power +3.0

Sink Current ILVI/O = 0.4V 4.0 mA

Standby Current IDDS (Notes 7, 8) 750 1000 nA

Active Current IDD VDD = 5V (Note 9) 1 1.5 mA

DQ Input Current IDQ (Note 10) 5 µA

Drift (Note 11) ±0.2 °C

Absolute Maximum Ratings

These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure

to absolute maximum rating conditions for extended periods of time may affect reliability.

DC Electrical Characteristics

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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(-55°C to +125°C; VDD = 3.0V to 5.5V)

Note 12: See the timing diagrams in Figure 2.

Note 13: Under parasite power, if tRSTL > 960µs, a power-on reset can occur.

Figure 1. Typical Performance Curve

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

NV Write Cycle Time tWR 2 10 ms

EEPROM Writes NEEWR -55°C to +55°C 50k writes

EEPROM Data Retention tEEDR -55°C to +55°C 10 years

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Temperature Conversion Time tCONV

9-bit resolution

(Note 12)

93.75

10-bit resolution 187.5

11-bit resolution 375

12-bit resolution 750

Time to Strong Pullup On tSPON Start convert T command issued 10 µs

Time Slot tSLOT (Note 12) 60 120 µs

Recovery Time tREC (Note 12) 1 µs

Write 0 Low Time tLOW0 (Note 12) 60 120 µs

Write 1 Low Time tLOW1 (Note 12) 1 15 µs

Read Data Valid tRDV (Note 12) 15 µs

Reset Time High tRSTH (Note 12) 480 µs

Reset Time Low tRSTL (Notes 12, 13) 480 µs

Presence-Detect High tPDHIGH (Note 12) 15 60 µs

Presence-Detect Low tPDLOW (Note 12) 60 240 µs

Capacitance CIN/OUT 25 pF

AC Electrical Characteristics–NV Memory

AC Electrical Characteristics

DS18B20 TYPICAL ERROR CURVE

0.5

0.4

0.3

0.2

0.1

-0.1

-0.2

-0.3

-0.4

-0.5

THERMOMETER ERROR (°C)

0 7010 20 30 40 50 60

TEMPERATURE (°C)

+3s ERROR

MEAN ERROR

-3s ERROR

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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Figure 2. Timing Diagrams

PIN NAME FUNCTION

SO µSOP TO-92

1, 2, 6,

7, 8

2, 3, 5,

6, 7 — N.C. No Connection

3 8 3 VDD Optional VDD. VDD must be grounded for operation in parasite power mode.

4 1 2 DQ Data Input/Output. Open-drain 1-Wire interface pin. Also provides power to the

device when used in parasite power mode (see the Powering the DS18B20 section.)

5 4 1 GND Ground

Pin Description

START OF NEXT CYCLE

1-WIRE WRITE ZERO TIME SLOT

REC

SLOT

LOW0

1-WIRE READ ZERO TIME SLOT

REC

SLOT

START OF NEXT CYCLE

RDV

1-WIRE RESET PULSE

1-WIRE PRESENCE DETECT

RSTL

RSTH

PDIH

PRESENCE DETECT

PDLOW

RESET PULSE FROM HOST

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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Overview

Figure 3 shows a block diagram of the DS18B20, and

pin descriptions are given in the Pin Description table.

The 64-bit ROM stores the device’s unique serial code.

The scratchpad memory contains the 2-byte temperature

sensor. In addition, the scratchpad provides access to the

1-byte upper and lower alarm trigger registers (TH and

TL) and the 1-byte configuration register. The configura-

tion register allows the user to set the resolution of the

temperature-to-digital conversion to 9, 10, 11, or 12 bits.

The TH, TL, and configuration registers are nonvolatile

(EEPROM), so they will retain data when the device is

powered down.

The DS18B20 uses Maxim’s exclusive 1-Wire bus proto-

col that implements bus communication using one control

signal. The control line requires a weak pullup resistor

since all devices are linked to the bus via a 3-state or

open-drain port (the DQ pin in the case of the DS18B20).

In this bus system, the microprocessor (the master

device) identifies and addresses devices on the bus

using each device’s unique 64-bit code. Because 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.

Another feature of the DS18B20 is the ability to oper-

ate without an external power supply. Power is instead

supplied through the 1-Wire pullup resistor through the

DQ pin when the bus is high. The high bus signal also

charges an internal capacitor (CPP), which then supplies

power to the device when the bus is low. This method of

deriving power from the 1-Wire bus is referred to as “para-

site power.” As an alternative, the DS18B20 may also be

Operation—Measuring Temperature

The core functionality of the DS18B20 is its direct-to-

digital temperature sensor. The resolution of the tempera-

ture 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-bit. The DS18B20 powers up in a low-

power idle state. To initiate a temperature measurement

and A-to-D conversion, the master must issue a Convert

T [44h] command. Following the conversion, the resulting

thermal data is stored in the 2-byte temperature register

in the scratchpad memory and the DS18B20 returns to its

idle state. If the DS18B20 is powered by an external sup-

ply, the master can issue “read time slots” (see the 1-Wire

Bus System section) after the Convert T command and

the DS18B20 will respond by transmitting 0 while the tem-

perature conversion is in progress and 1 when the con-

version is done. If the DS18B20 is powered with parasite

power, this notification technique cannot be used since

the bus must be pulled high by a strong pullup during the

entire temperature conversion. The bus requirements for

parasite power are explained in detail in the Powering the

DS18B20 section.

Figure 3. DS18B20 Block Diagram

TEMPERATURE

SENSOR

SCRATCHPAD

MEMORY

CONTROL LOGIC

64-BIT ROM

AND 1-Wire

PORT

PARASITE POWER CIRCUIT

POWER-

SUPPLY SENSE

INTERNAL VDD

GND

VPU

4.7kΩ

CONFIGURATION

8-BIT CRC

GENERATOR

VDD

CPP

DS18B20

ALARM LOW TRIGGER (T

)

ALARM HIGH TRIGGER (T

)

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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The DS18B20 output temperature data is calibrated in

degrees Celsius; for Fahrenheit applications, a lookup

table or conversion routine must be used. The tempera-

ture data is stored as a 16-bit sign-extended two’s comple-

ment number in the temperature register (see Figure 4).

The sign bits (S) indicate if the temperature is positive

or negative: for positive numbers S = 0 and for negative

numbers S = 1. If the DS18B20 is configured for 12-bit

resolution, all bits in the temperature register will contain

valid data. For 11-bit resolution, bit 0 is undefined. For

10-bit resolution, bits 1 and 0 are undefined, and for 9-bit

resolution bits 2, 1, and 0 are undefined. Table 1 gives

examples of digital output data and the corresponding

temperature reading for 12-bit resolution conversions.

Operation—Alarm Signaling

After the DS18B20 performs a temperature conversion,

the temperature value is compared to the user-defined

two’s complement alarm trigger values stored in the

1-byte TH and TL registers (see Figure 5). The sign bit (S)

indicates if the value is positive or negative: for positive

numbers S = 0 and for negative numbers S = 1. The TH

and TL registers are nonvolatile (EEPROM) so they will

retain data when the device is powered down. TH and TL

can be accessed through bytes 2 and 3 of the scratchpad

as explained in the Memory section.

Only bits 11 through 4 of the temperature register are

used in the TH and TL comparison since TH and TL are

8-bit registers. If the measured temperature is lower than

Figure 4. Temperature Register Format

Figure 5. TH and TL Register Format

Table 1. Temperature/Data Relationship

*The power-on reset value of the temperature register is +85°C.

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

LS BYTE 232221202-1 2-2 2-3 2-4

BIT 15 BIT 14 BIT 13 BIT 12 BIT 11 BIT 10 BIT 9 BIT 8

MS BYTE S S S S S 262524

S = SIGN

TEMPERATURE (°C) DIGITAL OUTPUT

(BINARY)

DIGITAL OUTPUT

(HEX)

+125 0000 0111 1101 0000 07D0h

+85* 0000 0101 0101 0000 0550h

+25.0625 0000 0001 1001 0001 0191h

+10.125 0000 0000 1010 0010 00A2h

+0.5 0000 0000 0000 1000 0008h

0 0000 0000 0000 0000 0000h

-0.5 1111 1111 1111 1000 FFF8h

-10.125 1111 1111 0101 1110 FF5Eh

-25.0625 1111 1110 0110 1111 FE6Fh

-55 1111 1100 1001 0000 FC90h

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

S 26252423222120

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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or equal to TL or higher than or equal to TH, an alarm con-

dition exists and an alarm flag is set inside the DS18B20.

This flag is updated after every temperature measure-

ment; therefore, if the alarm condition goes away, the flag

will be turned off after the next temperature conversion.

The master device can check the alarm flag status of

all DS18B20s on the bus by issuing an Alarm Search

[ECh] command. Any DS18B20s with a set alarm flag will

respond to the command, so the master can determine

exactly which DS18B20s have experienced an alarm

condition. If an alarm condition exists and the TH or TL

settings have changed, another temperature conversion

should be done to validate the alarm condition.

Powering the DS18B20

The DS18B20 can be powered by an external supply on

the VDD pin, or it can operate in “parasite power” mode,

which allows the DS18B20 to function without a local

external supply. Parasite power is very useful for applica-

tions that require remote temperature sensing or that are

very space constrained. Figure 3 shows the DS18B20’s

parasite-power control circuitry, which “steals” power from

the 1-Wire bus via the DQ pin when the bus is high. The

stolen charge powers the DS18B20 while the bus is high,

and some of the charge is stored on the parasite power

capacitor (CPP) to provide power when the bus is low.

When the DS18B20 is used in parasite power mode, the

VDD pin must be connected to ground.

In parasite power mode, the 1-Wire bus and CPP can pro-

vide sufficient current to the DS18B20 for most operations

as long as the specified timing and voltage requirements

are met (see the DC Electrical Characteristics and AC

Electrical Characteristics). However, when the DS18B20

is performing temperature conversions or copying 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 supplied

by CPP. To assure that the DS18B20 has sufficient supply

current, it is necessary to provide a strong pullup on the

1-Wire bus whenever temperature conversions are tak-

ing place or data is being copied from the scratchpad to

EEPROM. This can be accomplished by using a MOSFET

to pull the bus directly to the rail as shown in Figure 6. 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 (tCONV)

or data transfer (tWR = 10ms). No other activity can take

place on the 1-Wire bus while the pullup is enabled.

The DS18B20 can also be powered by the conventional

method of connecting an external power supply to the

VDD pin, as shown in Figure 7. The advantage of this

method is that the MOSFET pullup is not required, and

the 1-Wire bus is free to carry other traffic during the tem-

perature conversion time.

The use of parasite power is not recommended for tem-

peratures above +100°C since the DS18B20 may not be

able to sustain communications due to the higher leak-

age currents that can exist at these temperatures. For

applications in which such temperatures are likely, it is

strongly recommended that the DS18B20 be powered by

an external power supply.

In some situations the bus master may not know whether

the DS18B20s on the bus are parasite powered or pow-

ered by external supplies. The master needs this informa-

tion to determine if the strong bus pullup should be used

during temperature conversions. To get this information,

the master can issue a Skip ROM [CCh] command fol-

lowed by a Read Power Supply [B4h] command followed

by a “read time slot”. During the read time slot, parasite

powered DS18B20s will pull the bus low, and externally

powered DS18B20s will let the bus remain high. If the

bus is pulled low, the master knows that it must supply

the strong pullup on the 1-Wire bus during temperature

conversions.

Figure 6. Supplying the Parasite-Powered DS18B20 During

Temperature Conversions

Figure 7. Powering the DS18B20 with an External Supply

4.7kΩ

1-Wire BUS

DS18B20

GND DQ V

TO OTHER

1-Wire DEVICES

µP

4.7kΩ

1-Wire BUS

DS18B20

GND DQ V

TO OTHER

1-Wire DEVICES

µP

(EXTERNAL

SUPPLY)

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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64-BIT Lasered ROM code

Each DS18B20 contains a unique 64–bit code (see Figure

8) stored in ROM. The least significant 8 bits of the ROM

code contain the DS18B20’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 DS18B20

to operate as a 1-Wire device using the protocol detailed

in the 1-Wire Bus System section.

Memory

The DS18B20’s memory is organized as shown in Figure

9. The memory consists of an SRAM scratchpad with

nonvolatile EEPROM storage for the high and low alarm

trigger registers (TH and TL) and configuration register.

Note that if the DS18B20 alarm function is not used,

the TH and TL registers can serve as general-purpose

memory. All memory commands are described in detail in

the DS18B20 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 TH

and TL registers. Byte 4 contains the configuration regis-

ter data, which is explained in detail in the Configuration

nal use by the device and cannot be overwritten.

Byte 8 of the scratchpad is read-only and contains the

CRC code for bytes 0 through 7 of the scratchpad.

The DS18B20 generates this CRC using the method

described in the CRC Generation section.

Data is written to bytes 2, 3, and 4 of the scratchpad using

the Write Scratchpad [4Eh] command; the data must be

transmitted to the DS18B20 starting with the least signifi-

cant 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 TH, TL 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 E2 [B8h] command. The

master can issue read time slots following the Recall E2

command and the DS18B20 will indicate the status of the

recall by transmitting 0 while the recall is in progress and

1 when the recall is done.

Figure 8. 64-Bit Lasered ROM Code

Figure 9. DS18B20 Memory Map

8-BIT CRC 48-BIT SERIAL NUMBER 8-BIT FAMILY CODE (28h)

MSB LSB MSB LSB MSB LSB

BYTE 0

BYTE 1

TEMPERATURE LSB (50h)

TEMPERATURE MSB (05h) (85°C)

BYTE 2

BYTE 3

TH REGISTER OR USER BYTE 1*

TL REGISTER OR USER BYTE 2*

BYTE 4

BYTE 5

CONFIGURATION REGISTER*

RESERVED (FFh)

BYTE 6

BYTE 7

RESERVED

RESERVED (10h)

BYTE 8 CRC*

*POWER-UP STATE DEPENDS ON VALUE(S) STORED IN EEPROM.

TH REGISTER OR USER BYTE 1*

TL REGISTER OR USER BYTE 2*

CONFIGURATION REGISTER*

SCRATCHPAD

(POWER-UP STATE)

EEPROM

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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Conguration Register

Byte 4 of the scratchpad memory contains the configura-

tion register, which is organized as illustrated in Figure 10.

The user can set the conversion resolution of the DS18B20

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 tradeoff

between resolution and conversion time. Bit 7 and bits 0 to

4 in the configuration register are reserved for internal use

by the device and cannot be overwritten.

CRC Generation

CRC bytes are provided as part of the DS18B20’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 it chang-

es 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 DS18B20. To verify that data

has been read correctly, the bus master must re-calculate

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 cal-

culated 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

DS18B20 that prevents a command sequence from pro-

ceeding if the DS18B20 CRC (ROM or scratchpad) does

not match the value generated by the bus master.

The equivalent polynomial function of the CRC (ROM or

scratchpad) is:

CRC = X8 + X5 + X4 + 1

The bus master can re-calculate the CRC and compare it

to the CRC values from the DS18B20 using the polyno-

mial generator shown in Figure 11. This circuit consists

of a shift register and XOR gates, and the shift register

bits are initialized to 0. Starting with the least significant

bit of the ROM code or the least significant bit of byte 0

in the scratchpad, one bit at a time should shifted into the

shift register. After shifting in the 56th bit from the ROM or

the most significant bit of byte 7 from the scratchpad, the

polynomial generator will contain the recalculated CRC.

Next, the 8-bit ROM code or scratchpad CRC from the

DS18B20 must be shifted into the circuit. At this point, if

the re-calculated CRC was correct, the shift register will

contain all 0s. Additional information about the Maxim

1-Wire cyclic redundancy check is available in Application

Note 27: Understanding and Using Cyclic Redundancy

Checks with Maxim iButton Products.

Figure 10. Configuration Register

Figure 11. CRC Generator

Table 2. Thermometer Resolution Configuration

R1 R0 RESOLUTION

(BITS) MAX CONVERSION TIME

0 0 9 93.75ms (tCONV/8)

0 1 10 187.5ms (tCONV/4)

1 0 11 375ms (tCONV/2)

1 1 12 750ms (tCONV)

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

0 R1 R0 1 1 1 1 1

XOR XOR XOR

INPUT

MSB LSB

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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1-Wire Bus System

The 1-Wire bus system uses a single bus master to con-

trol one or more slave devices. The DS18B20 is always a

slave. When there is only one slave on the bus, the sys-

tem is referred to as a “single-drop” system; the system 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.

The following discussion of the 1-Wire bus system is

broken down into three topics: hardware configuration,

transaction sequence, and 1-Wire signaling (signal types

and timing).

Hardware Conguration

The 1-Wire bus has by definition only a single data line.

Each device (master or slave) interfaces to the data line

via an open-drain or 3-state port. This allows each device

to “release” the data line when the device is not transmit-

ting data so the bus is available for use by another device.

The 1-Wire port of the DS18B20 (the DQ pin) is open

drain with an internal circuit equivalent to that shown in

Figure 12.

The 1-Wire bus requires an external pullup resistor of

approximately 5kΩ; thus, the idle state for the 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.

Transaction Sequence

The transaction sequence for accessing the DS18B20 is

as follows:

Step 1. Initialization

Step 2. ROM Command (followed by any required data

exchange)

Step 3. DS18B20 Function Command (followed by any

required data exchange)

It is very important to follow this sequence every time the

DS18B20 is accessed, as the DS18B20 will not respond

if any steps in the sequence are missing or out of order.

Exceptions to this rule are the Search ROM [F0h] and

Alarm Search [ECh] commands. After issuing either of

these ROM commands, the master must return to Step 1

in the sequence.

Initialization

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 DS18B20) are on the bus and are ready

to operate. Timing for the reset and presence pulses is

detailed in the 1-Wire Signaling section.

ROM Commands

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

issuing a DS18B20 function command. A flowchart for

operation of the ROM commands is shown in Figure 13.

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 master to perform a Search ROM cycle (i.e., Search

ROM command followed by data exchange) as many

times as necessary to identify all of the slave devices.

Figure 12. Hardware Configuration

4.7kΩ

DS18B20

1-Wire PORT

100Ω

MOSFET

5µA

TYP

1-Wire BUS

Rx = RECEIVE

Tx = TRANSMIT

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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If there is only one slave on the bus, the simpler Read

ROM [33h] command can be used in place of the Search

ROM process. For a detailed explanation of the Search

ROM procedure, refer to Application Note 937: Book of

iButton® Standards. After every Search ROM cycle, the

bus master must return to Step 1 (Initialization) in the

transaction sequence.

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-bit ROM code without using the Search ROM proce-

dure. If this command is used when there is more than

one slave present on the bus, a data collision will occur

when all the slaves attempt to respond at the same time.

Match Rom [55H]

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 will respond to the function command issued

by the master; all other slaves on the bus will wait for a

reset pulse.

Skip Rom [CCh]

The master can use this command to address all devices

on the bus simultaneously without sending out any ROM

code information. For example, the master can make all

DS18B20s on the bus perform simultaneous temperature

conversions by issuing a Skip ROM command followed by

a Convert T [44h] command.

Note that the Read Scratchpad [BEh] command can

follow the Skip ROM command only if there is a single

slave device on the bus. In this case, time is saved by

allowing the master to read from the slave without send-

ing the device’s 64-bit ROM code. A Skip ROM command

followed by a Read Scratchpad command will cause

a data collision on the bus if there is more than one

slave since multiple devices will attempt to transmit data

simultaneously.

Alarm Search [ECh]

The operation of this command is identical to the operation

of the Search ROM command except that only slaves with

a set alarm flag will respond. This command allows the

master device to determine if any DS18B20s experienced

an alarm condition during the most recent temperature

conversion. After every Alarm Search cycle (i.e., Alarm

Search command followed by data exchange), the bus

master must return to Step 1 (Initialization) in the transac-

tion sequence. See the Operation—Alarm Signaling sec-

tion for an explanation of alarm flag operation.

DS18B20 Function Commands

After the bus master has used a ROM command to

address the DS18B20 with which it wishes to communi-

cate, the master can issue one of the DS18B20 function

commands. These commands allow the master to write

to and read from the DS18B20’s scratchpad memory,

initiate temperature conversions and determine the power

supply mode. The DS18B20 function commands, which

are described below, are summarized in Table 3 and illus-

trated by the flowchart in Figure 14.

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 DS18B20 returns to its low-power

idle state. If the device is being used in parasite power

mode, 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 (tCONV) as described

in the Powering the DS18B20 section. If the DS18B20 is

time slots after the Convert T command and the DS18B20

will respond by transmitting a 0 while the temperature

conversion is in progress and a 1 when the conversion is

done. In parasite power mode this notification technique

cannot be used since the bus is pulled high by the strong

pullup during the conversion.

Write Scratchpad [4Eh]

This command allows the master to write 3 bytes of data

to the DS18B20’s scratchpad. The first data byte is written

into the TH register (byte 2 of the scratchpad), the second

byte is written into the TL 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 sig-

nificant bit of byte 0 and continues through the scratchpad

until the 9th byte (byte 8 – CRC) is read. The master may

issue a reset to terminate reading at any time if only part

of the scratchpad data is needed.

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DS18B20 Programmable Resolution

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Copy Scratchpad [48h]

This command copies the contents of the scratchpad

TH, TL and configuration registers (bytes 2, 3 and 4) to

EEPROM. If the device is being used in parasite power

mode, 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 Powering the DS18B20

section.

Recall E2 [B8h]

This command recalls the alarm trigger values (TH and

TL) 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

following the Recall E2 command and the DS18B20 will

indicate 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.

Read Power Supply [B4h]

The master device issues this command followed by a

read time slot to determine if any DS18B20s on the bus

are using parasite power. During the read time slot, para-

site powered DS18B20s will pull the bus low, and exter-

nally powered DS18B20s will let the bus remain high. See

the Powering the DS18B20 section for usage information

for this command.

Table 3. DS18B20 Function Command Set

Note 1: For parasite-powered DS18B20s, the master must enable a strong pullup on the 1-Wire bus during temperature conver-

sions and copies from the scratchpad to EEPROM. No other bus activity may 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 three bytes must be written before a reset is issued.

COMMAND DESCRIPTION PROTOCOL 1-Wire BUS ACTIVITY AFTER

COMMAND IS ISSUED NOTES

TEMPERATURE CONVERSION COMMANDS

Convert T Initiates temperature conversion. 44h

DS18B20 transmits conversion status

to master (not applicable for parasite-

powered DS18B20s).

MEMORY COMMANDS

Read

Scratchpad

Reads the entire scratchpad including the

CRC byte. BEh DS18B20 transmits up to 9 data bytes

to master. 2

Write

Scratchpad

Writes data into scratchpad bytes 2, 3, and

4 (TH, TL, and conguration registers). 4Eh Master transmits 3 data bytes to

DS18B20. 3

Copy

Scratchpad

Copies TH, TL, and conguration register

data from the scratchpad to EEPROM. 48h None 1

Recall E2Recalls TH, TL, and conguration register

data from EEPROM to the scratchpad. B8h DS18B20 transmits recall status to

master.

Read Power

Supply

Signals DS18B20 power supply mode to

the master. B4h DS18B20 transmits supply status to

master.

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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Figure 13. ROM Commands Flowchart

MASTER Tx

ROM COMMAND

DS18B20 Tx PRESENCE PULSE

MASTER Tx RESET PULSE

INITIALIZATION

SEQUENCE

33h READ

ROM

COMMAND

55h MATCH

ROM

COMMAND

F0h

SEARCH ROM

COMMAND

ECh

ALARM SEARCH

COMMAND

CCh

SKIP ROM

COMMAND

MASTER Tx

BIT 0

DS18B20 Tx BIT 0

MASTER Tx BIT 0

BIT 0

MATCH ?

BIT 0

MATCH ?

DEVICE(S)

WITH ALARM

FLAG SET ?

MASTER Tx

BIT 1

DS18B20 Tx BIT 1

MASTER Tx BIT 1

BIT 1

MATCH?

BIT 1

MATCH?

Y Y

DS18B20 Tx BIT 63

MASTER Tx BIT 63

MASTER Tx

BIT 63

DS18B20 Tx BIT 0

MASTER TX BIT 0

BIT 63

MATCH?

BIT 63

MATCH?

Y Y

DS18B20 TX

FAMILY CODE 1

BYTE

DS18B20 Tx

SERIAL NUMBER

6 BYTES

DS18B20 Tx

CRC BYTE

MASTER Tx FUNCTION

COMMAND (FIGURE 14)

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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Figure 14. DS18B20 Function Commands Flowchart

MASTER Tx

FUNCTION COMMAND

44h CONVERT

TEMPERATURE ?

PARASITE

POWER ?

DS18B20 BEGINS

CONVERSION

DEVICE

CONVERTING

TEMPERATURE ?

MASTER

Rx “0s”

MASTER

Rx “1s”

MASTER ENABLES STRONG

PULL-UP ON DQ

DS18B20 CONVERTS

TEMPERATURE

MASTER DISABLES

STRONG PULLUP

B4h READ

POWER SUPPLY ?

PARASITE

POWER ?

MASTER

Rx “1s”

MASTER

Rx “0s”

B8h

RECALL E

MASTER BEGINS

DATA RECALL FROM

E2 PROM

DEVICE BUSY

RECALLING

DATA ?

MASTER

Rx “0s”

MASTER

Rx “1s”

BEh READ

SCRATCHPAD ?

MASTER Rx DATA

BYTE FROM

SCRATCHPAD

MASTER Tx

RESET ?

HAVE 8 BYTES

BEEN READ ?

MASTER Rx

SCRATCHPAD CRC

BYTE

MASTER Tx TH BYTE TO

SCRATCHPAD

MASTER Tx TL BYTE TO

SCRATCHPAD

MASTER TX CONFIG. BYTE

TO SCRATCHPAD

4Eh WRITE

SCRATCHPAD ?

48h COPY

SCRATCHPAD ?

PARASITE

POWER ?

COPY IN

PROGRESS ?

MASTER

Rx “0s”

MASTER

Rx “1s”

MASTER ENABLES STRONG

PULL-UP ON DQ

DATA COPIED FROM

SCRATCHPAD TO EEPROM

MASTER DISABLES

STRONG PULLUP

RETURN TO INITIALIZATION

SEQUENCE (FIGURE 13)

FOR NEXT TRANSACTION

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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1-Wire Signaling

The DS18B20 uses a strict 1-Wire communication pro-

tocol to ensure data integrity. Several signal types are

defined by this protocol: reset pulse, presence pulse, write

0, write 1, read 0, and read 1. The bus master initiates all

these signals, with the exception of the presence pulse.

Initialization Procedure—Reset And

Presence Pulses

All communication with the DS18B20 begins with an ini-

tialization sequence that consists of a reset pulse from the

master followed by a presence pulse from the DS18B20.

This is illustrated in Figure 15. When the DS18B20 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.

During the initialization sequence the bus master trans-

mits (TX) the reset pulse by pulling the 1-Wire bus low

for a minimum of 480µs. The bus master then releases

the bus and goes into receive mode (RX). When the bus

is released, the 5kΩ pullup resistor pulls the 1-Wire bus

high. When the DS18B20 detects this rising edge, it waits

15µs to 60µs and then transmits a presence pulse by pull-

ing the 1-Wire bus low for 60µs to 240µs.

Read/Write Time Slots

The bus master writes data to the DS18B20 during write

time slots and reads data from the DS18B20 during read

time slots. One bit of data is transmitted over the 1-Wire

bus per time slot.

Write Time Slots

There are two types of write time slots: “Write 1” time slots

and “Write 0” time slots. The bus master uses a Write 1

time slot to write a logic 1 to the DS18B20 and a Write

0 time slot to write a logic 0 to the DS18B20. All write

time slots must be a minimum of 60µs in duration with a

minimum of a 1µs recovery time between individual write

slots. Both types of write time slots are initiated by the

master pulling the 1-Wire bus low (see Figure 14).

To generate a Write 1 time slot, after pulling the 1-Wire

bus low, the bus master must release the 1-Wire bus

within 15µs. When the bus is released, the 5kΩ pullup

resistor will pull the bus high. To generate a Write 0 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).

The DS18B20 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 win-

dow, a 1 is written to the DS18B20. If the line is low, a 0

is written to the DS18B20.

Figure 15. Initialization Timing

LINE TYPE LEGEND

DS18B20 PULLING LOW

RESISTOR PULLUP

MASTER Tx RESET PULSE

480µs MINIMUM

MASTER Rx

480µs MINIMUM

DS18B20

WAITS 15-60µs

1-Wire BUS

GND

DS18B20 TX PRESENCE

PULSE 60-240µS

BUS MASTER PULLING LOW

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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Read Time Slots

The DS18B20 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

a Read Scratchpad [BEh] or Read Power Supply [B4h]

command, so that the DS18B20 can provide the request-

ed data. In addition, the master can generate read time

slots after issuing Convert T [44h] or Recall E2 [B8h] com-

mands to find out the status of the operation as explained

in the DS18B20 Function Commands section.

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 (see Figure 16). After the master initiates the

read time slot, the DS18B20 will begin transmitting a 1

or 0 on bus. The DS18B20 transmits a 1 by leaving the

bus high and transmits a 0 by pulling the bus low. When

transmitting a 0, the DS18B20 will release the bus by the

end of the time slot, and the bus will be pulled back to

its high idle state by the pullup resister. Output data from

the DS18B20 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.

Figure 17 illustrates that the sum of TINIT, TRC, and

TSAMPLE must be less than 15µs for a read time slot.

Figure 18 shows that system timing margin is maximized

by keeping TINIT and TRC as short as possible and by

locating the master sample time during read time slots

towards the end of the 15µs period.

Figure 16. Read/Write Time Slot Timing Diagram

MASTER WRITE “0” SLOT

MASTER WRITE “1” SLOT

MASTER READ “0” SLOT MASTER READ “1” SLOT

60µs < Tx “0” < 120µs

START

OF SLOT

START

OF SLOT

1µs < T

REC

< ∞

1µs

MIN TYP MAX

DS18B20 SAMPLES

15µs 15µs 30µs

MIN TYP MAX

DS18B20 SAMPLES

15µs 15µs 30µs

1-Wire BUS

GND

1-Wire BUS

GND

1µs < T

REC

< ∞

15µs

> 1µs

MASTER SAMPLES

45µs

MASTER SAMPLES

> 1µs

15µs

LINE TYPE LEGEND

RESISTOR PULLUPDS18B20 PULLING LOWBUS MASTER PULLING LOW

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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Related Application Notes

The following application notes can be

applied to the DS18B20 and are available at

www.maximintegrated.com.

Application Note 27: Understanding and Using Cyclic

Redundancy Checks with Maxim iButton Products

Application Note 122: Using Dallas’ 1-Wire ICs in 1-Cell

Li-Ion Battery Packs with Low-Side N-Channel Safety

FETs Master

Application Note 126: 1-Wire Communication Through

Software

Application Note 162: Interfacing the DS18x20/DS1822

1-Wire Temperature Sensor in a Microcontroller

Environment

Application Note 208: Curve Fitting the Error of a

Bandgap-Based Digital Temperature Sensor

Application Note 2420: 1-Wire Communication with a

Microchip PICmicro Microcontroller

Application Note 3754: Single-Wire Serial Bus Carries

Isolated Power and Data

Sample 1-Wire subroutines that can be used in conjunc-

tion with Application Note 74: Reading and Writing iBut-

tons via Serial Interfaces can be downloaded from the

Maxim website.

Figure 17. Detailed Master Read 1 Timing

Figure 18. Recommended Master Read 1 Timing

VIH OF MASTER

MASTER SAMPLES

1-Wire BUS

GND

15µs

INT

> 1µs T

VIH OF MASTER

LINE TYPE LEGEND

RESISTOR PULLUP

BUS MASTER PULLING LOW

MASTER SAMPLES

15µs

TINT =

SMALL

TRC =

SMALL

VPU

1-Wire BUS

GND

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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DS18B20 Operation Example 1

In this example there are multiple DS18B20s on the bus

and they are using parasite power. The bus master initi-

ates a temperature conversion in a specific DS18B20 and

then reads its scratchpad and recalculates the CRC to

verify the data.

DS18B20 Operation Example 2

In this example there is only one DS18B20 on the bus and

it is using parasite power. The master writes to the TH, TL,

and configuration registers in the DS18B20 scratchpad

and then reads the scratchpad and recalculates the CRC

to verify the data. The master then copies the scratchpad

contents to EEPROM.

MASTER

MODE

DATA

(LSB FIRST) COMMENTS

Tx Reset Master issues reset pulse.

Rx Presence DS18B20s respond with

presence pulse.

Tx 55h Master issues Match ROM

command.

Tx 64-bit ROM

code

Master sends DS18B20 ROM

code.

Tx 44h Master issues Convert T

command.

DQ line

held high by

strong pullup

Master applies strong pullup

to DQ for the duration of the

conversion (tCONV).

Tx Reset Master issues reset pulse.

Rx Presence DS18B20s respond with

presence pulse.

Tx 55h Master issues Match ROM

command.

Tx 64-bit ROM

code

Master sends DS18B20 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 eight 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 DS18B20 responds with

presence pulse.

Tx CCh Master issues Skip ROM

command.

Tx 4Eh Master issues Write Scratchpad

command.

Tx 3 data bytes

Master sends three data bytes

to scratchpad (TH, TL, and

cong).

Tx Reset Master issues reset pulse.

Rx Presence DS18B20 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 eight 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 DS18B20 responds with

presence pulse.

Tx CCh Master issues Skip ROM

command.

Tx 48h Master issues Copy Scratchpad

command.

DQ line

held high by

strong pullup

Master applies strong pullup to

DQ for at least 10ms while copy

operation is in progress.

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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+Denotes a lead-free package. A “+” will appear on the top mark of lead-free packages.

T&R = Tape and reel.

*TO-92 packages in tape and reel can be ordered with straight or formed leads. Choose “SL” for straight leads. Bulk TO-92 orders

are straight leads only.

PART TEMP RANGE PIN-PACKAGE TOP MARK

DS18B20 -55°C to +125°C 3 TO-92 18B20

DS18B20+ -55°C to +125°C 3 TO-92 18B20

DS18B20/T&R -55°C to +125°C 3 TO-92 (2000 Piece) 18B20

DS18B20+T&R -55°C to +125°C 3 TO-92 (2000 Piece) 18B20

DS18B20-SL/T&R -55°C to +125°C 3 TO-92 (2000 Piece)* 18B20

DS18B20-SL+T&R -55°C to +125°C 3 TO-92 (2000 Piece)* 18B20

DS18B20U -55°C to +125°C 8 FSOP 18B20

DS18B20U+ -55°C to +125°C 8 FSOP 18B20

DS18B20U/T&R -55°C to +125°C 8 FSOP (3000 Piece) 18B20

DS18B20U+T&R -55°C to +125°C 8 FSOP (3000 Piece) 18B20

DS18B20Z -55°C to +125°C 8 SO DS18B20

DS18B20Z+ -55°C to +125°C 8 SO DS18B20

DS18B20Z/T&R -55°C to +125°C 8 SO (2500 Piece) DS18B20

DS18B20Z+T&R -55°C to +125°C 8 SO (2500 Piece) DS18B20

Ordering Information

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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REVISION

DATE DESCRIPTION PAGES

CHANGED

030107 In the Absolute Maximum Ratings section, removed the reow oven temperature value of +220°C.

Reference to JEDEC specication for reow remains. 19

101207

In the Operation—Alarm Signaling section, added “or equal to” in the description for a TH alarm

condition 5

In the Memory section, removed incorrect text describing memory. 7

In the Conguration Register section, removed incorrect text describing conguration register. 8

042208 In the Ordering Information table, added TO-92 straight-lead packages and included a note that the

TO-92 package in tape and reel can be ordered with either formed or straight leads. 2

1/15 Updated Benets and Features section 1

09/18 Updated DC Electrical Characteristics table 2

Revision History

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 specications 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.

DS18B20 Programmable Resolution

1-Wire Digital Thermometer

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