DS18S20+T&R - Maxim Integrated

Pin Congurations

General Description

The DS18S20 digital thermometer provides 9-bit Celsius

temperature measurements and has an alarm function

with nonvolatile user-programmable upper and lower trig-

ger points. The DS18S20 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 DS18S20 can derive power directly from

the data line (“parasite power”), eliminating the need for

an external power supply.

Each DS18S20 has a unique 64-bit serial code, which

allows multiple DS18S20s to function on the same 1-Wire

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

control many DS18S20s 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

●Maximize System Accuracy in Broad Range of

Thermal Management Applications

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

(-67°F to +257°F)

• ±0.5°C Accuracy from -10°C to +85°C

• 9-Bit Resolution

• No External Components Required

●Parasite 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) and 3-Pin TO-92

Packages

Ordering Information appears at end of data sheet.

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

19-5474; Rev 3; 4/15

BOTTOM VIEW

N.C.

VDD

N.C.

GND

DS18S20

SO (150 mils)

(DS18S20Z)

DS18S20

1 2 3

GND DQ VDD

1 2 3

TOP VIEW

TO-92

(DS18S20)

DS18S20 High-Precision 1-Wire Digital Thermometer

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

Continuous Power Dissipation (TA = +70°C)

8-Pin SO (derate 5.9mW/°C above +70°C) .............. 470.6mW

3-Pin TO-92 (derate 6.3mW/°C above +70°C) ............ 500mW

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

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

Lead Temperature (soldering, 10s) .................................+260°C

Soldering Temperature (reflow)

Lead(Pb)-free...............................................................+260°C

Containing lead(Pb) ..................................................... +240°C

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 pul-

lup is equal to VPU. In order to meet the VIH spec of the DS18S20, the actual supply rail for the strong pullup transistor

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.

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.

(VDD = 3.0V to 5.5V, TA = -55°C to +125°C, unless otherwise noted.)

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 (Note 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

-55°C to +125°C ±2

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

Input Logic-High VIH

Local Power

(Note 1, 6)

+2.2 The lower of

5.5 or VDD

+ 0.3

Parasite Power +3.0

Sink Current ILVI/O = 0.4V (Note 1) 4.0 mA

Standby Current IDDS (Note 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

DS18S20 High-Precision 1-Wire Digital Thermometer

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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

(VDD = 3.0V to 5.5V, TA = -55°C to +100°C, unless otherwise noted.)

(VDD = 3.0V to 5.5V; TA = -55°C to +125°C, unless otherwise noted.)

Note 12: See the timing diagrams in Figure 2.

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

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 (Note 12) 750 ms

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 (Note 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

Figure 1. Typical Performance Curve

DS18S20 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

DS18S20 High-Precision 1-Wire Digital Thermometer

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AC Electrical Characteristics—NV Memory

AC Electrical Characteristics

PIN NAME FUNCTION

TO-92 SO

15 GND Ground

24 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 DS18S20 section.)

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

—1, 2, 6, 7, 8 N.C. No Connection

Figure 2. Timing Diagrams

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

PDHIGH

PRESENCE DETECT

PDLOW

RESET PULSE FROM HOST

DS18S20 High-Precision 1-Wire Digital Thermometer

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Pin Description

Overview

Figure 3 shows a block diagram of the DS18S20, 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). The TH and TL registers are nonvolatile (EEPROM),

so they will retain data when the device is powered down.

The DS18S20 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 DS18S20).

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 DS18S20 is the ability to operate

without an external power supply. Power is instead sup-

plied through the 1-Wire pullup resistor via 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 “parasite power.” As

an alternative, the DS18S20 may also be powered by an

external supply on VDD.

Operation—Measuring Temperature

The core functionality of the DS18S20 is its direct-to-dig-

ital temperature sensor. The temperature sensor output

has 9-bit resolution, which corresponds to 0.5°C steps.

The DS18S20 powers-up in a low-power idle state; to

initiate a temperature measurement and A-to-D conver-

sion, 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 scratch-

pad memory and the DS18S20 returns to its idle state.

If the DS18S20 is powered by an external supply, the

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

System section) after the Convert T command and the

DS18S20 will respond by transmitting 0 while the tem-

perature conversion is in progress and 1 when the con-

version is done. If the DS18S20 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

DS18S20 section.

Figure 3. DS18S20 Block Diagram

64-BIT ROM

AND

1-Wire PORT

INTERNAL V

PARASITE POWER CIRCUIT MEMORY

CONTROL LOGIC

SCRATCHPAD

8-BIT CRC

GENERATOR

TEMPERATURE

SENSOR

ALARM HIGH TRIGGER (T

)

ALARM LOW TRIGGER (T

)

GND

DS18S20

4.7kΩ

POWER-

SUPPLY SENSE

DS18S20 High-Precision 1-Wire Digital Thermometer

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The DS18S20 output data is calibrated in degrees cen-

tigrade; for Fahrenheit applications, a lookup table or

conversion routine must be used. The temperature data is

stored as a 16-bit sign-extended two’s complement num-

ber 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. Table 1 gives examples of digital output data and the

corresponding temperature reading.

Resolutions greater than 9 bits can be calculated using the

data from the temperature, COUNT REMAIN and COUNT

PER °C registers in the scratchpad. Note that the COUNT

PER °C register is hard-wired to 16 (10h). After reading

the scratchpad, the TEMP_READ value is obtained by

truncating the 0.5°C bit (bit 0) from the temperature data

(see Figure 4). The extended resolution temperature can

then be calculated using the following equation:

TEMPERATURE TEMP_READ 0.25

COUNT_PER_C COUNT_REMAIN

COUNT_PER_C

= −

−

Operation—Alarm Signaling

After the DS18S20 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 8 through 1 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 or

equal to TL or higher than TH, an alarm condition exists

and an alarm flag is set inside the DS18S20. This flag is

updated after every temperature measurement; therefore,

if the alarm condition goes away, the flag will be turned off

after the next temperature conversion.

Table 1. Temperature/Data Relationship

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

TEMPERATURE (°C) DIGITAL OUTPUT (BINARY) DIGITAL OUTPUT (HEX)

+85.0* 0000 0000 1010 1010 00AAh

+25.0 0000 0000 0011 0010 0032h

+0.5 0000 0000 0000 0001 0001h

0 0000 0000 0000 0000 0000h

-0.5 1111 1111 1111 1111 FFFFh

-25.0 1111 1111 1100 1110 FFCEh

-55.0 1111 1111 1001 0010 FF92h

Figure 4. Temperature Register Format

Figure 5. TH and TL Register Format

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

LS BYTE 262524232221202-1

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

MS BYTE S S S S S S S S

S = SIGN

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

S 26252525222120

DS18S20 High-Precision 1-Wire Digital Thermometer

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The master device can check the alarm flag status of

all DS18S20s on the bus by issuing an Alarm Search

[ECh] command. Any DS18S20s with a set alarm flag will

respond to the command, so the master can determine

exactly which DS18S20s 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 DS18S20

The DS18S20 can be powered by an external supply on

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

which allows the DS18S20 to function without a local

external supply. Parasite power is very useful for applica-

tions that require remote temperature sensing or those

with space constraints. Figure 3 shows the DS18S20’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 DS18S20 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 DS18S20 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

provide sufficient current to the DS18S20 for most opera-

tions as long as the specified timing and voltage require-

ments are met (see the DC Electrical Characteristics

and the AC Electrical Characteristics). However, when

the DS18S20 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 DS18S20

has sufficient 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 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 DS18S20 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 DS18S20 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 DS18S20 be powered by

an external power supply.

In some situations the bus master may not know whether

the DS18S20s 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 DS18S20s will pull the bus low, and externally

powered DS18S20s 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 DS18S20 During

Temperature Conversions

Figure 7. Powering the DS18S20 with an External Supply

VPU

4.7kΩ

VPU

1-Wire BUS

DS18S20

GND DQ VDD

TO OTHER

1-Wire DEVICES

µP

(EXTERNAL SUPPLY)

4.7kΩ

1-Wire BUS

DS18S20

GND DQ V

TO OTHER

1-Wire DEVICES

µP

DS18S20 High-Precision 1-Wire Digital Thermometer

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64-Bit Lasered ROM Code

Each DS18S20 contains a unique 64-bit code (see

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

ROM code contain the DS18S20’s 1-Wire family code:

10h. 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 DS18S20 to operate as a 1-Wire device using

the protocol detailed in the 1-Wire Bus System section.

Memory

The DS18S20’s memory is organized as shown in

Figure 9. The memory consists of an SRAM scratch-

pad with nonvolatile EEPROM storage for the high and

low alarm trigger registers (TH and TL). Note that if the

DS18S20 alarm function is not used, the TH and TL reg-

isters can serve as general-purpose memory. All mem-

ory commands are described in detail in the DS18S20

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. Bytes 4 and 5 are reserved for internal

use by the device and cannot be overwritten; these bytes

will return all 1s when read. Bytes 6 and 7 contain the

COUNT REMAIN and COUNT PER ºC registers, which

can be used to calculate extended resolution results as

explained in the Operation—Measuring Temperature

section.

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

CRC code for bytes 0 through 7 of the scratchpad.

The DS18S20 generates this CRC using the method

described in the CRC Generation section.

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

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

transmitted to the DS18S20 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 and TL

data from the scratchpad to EEPROM, the master must

issue the Copy Scratchpad [48h] command.

Figure 8. 64-Bit Lasered ROM Code

Figure 9. DS18S20 Memory Map

8-BIT CRC 48-BIT SERIAL NUMBER 8-BIT FAMILY CODE (10h)

MSB LSB MSB LSB MSB LSB

BYTE 0

BYTE 1

TEMPERATURE LSB (AAh)

TEMPERATURE MSB (00h) (85°C)

BYTE 2

BYTE 3

BYTE 4

BYTE 5

RESERVED (FFh)

BYTE 6

BYTE 7

COUNT REMAIN (0Ch)

COUNT PER °C (10h)

BYTE 8 CRC*

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

SCRATCHPAD

(POWER-UP STATE)

EEPROM

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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” (see the 1-Wire

Bus System section) following the Recall E2 command

and the DS18S20 will indicate the status of the recall by

transmitting 0 while the recall is in progress and 1 when

the recall is done.

CRC Generation

CRC bytes are provided as part of the DS18S20’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 DS18S20. 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

DS18S20 that prevents a command sequence from pro-

ceeding if the DS18S20 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 DS18S20 using the polyno-

mial generator shown in Figure 10. 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 re-calculated CRC.

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

DS18S20 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 ịButton Products.

1-Wire Bus System

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

trol one or more slave devices. The DS18S20 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).

Figure 10. CRC Generator

(MSB) (LSB)

XOR XOR XOR

INPUT

DS18S20 High-Precision 1-Wire Digital Thermometer

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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 transmitting

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

1-Wire port of the DS18S20 (the DQ pin) is open drain with

an internal circuit equivalent to that shown in Figure 11.

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 DS18S20 is

as follows:

Step 1. Initialization

Step 2. ROM Command (followed by any required data

exchange)

Step 3. DS18S20 Function Command (followed by any

required data exchange)

It is very important to follow this sequence every time the

DS18S20 is accessed, as the DS18S20 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 DS18S20) 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 com-

mands, and each command is 8 bits long. The master

device must issue an appropriate ROM command before

issuing a DS18S20 function command. A flowchart for

operation of the ROM commands is shown in Figure 16.

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. If there is

only one slave on the bus, the simpler Read ROM com-

mand (see below) can be used in place of the Search

ROM process. For a detailed explanation of the Search

ROM procedure, refer to the ịButton® Book of Standards

at www.maximintegrated.com/ibuttonbook. 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.

ịButton is a registered trademark of Maxim Integrated Products, Inc.

Figure 11. Hardware Configuration

VPU

4.7kΩ DS18S20

1-Wire PORT

100Ω

MOSFET

5µA

TYP

1-Wire BUS

Rx = RECEIVE

Tx = TRANSMIT

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Note 1: For parasite-powered DS18S20s, 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: Both bytes must be written before a reset is issued.

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

DS18S20s 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 fol-

low 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 sending 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 DS18S20s 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.

DS18S20 Function Commands

After the bus master has used a ROM command to

address the DS18S20 with which it wishes to communi-

cate, the master can issue one of the DS18S20 function

commands. These commands allow the master to write

to and read from the DS18S20’s scratchpad memory,

initiate temperature conversions and determine the power

supply mode. The DS18S20 function commands, which

are described below, are summarized in Table 2 and illus-

trated by the flowchart in Figure 17.

Table 2. DS18S20 Function Command Set

COMMAND DESCRIPTION PROTOCOL 1-Wire BUS ACTIVITY AFTER

COMMAND IS ISSUED NOTES

TEMPERATURE CONVERSION COMMANDS

Convert T Initiates temperature

conversion. 44h

DS18S20 transmits conversion status

to master (not applicable for parasite-

powered DS18S20s).

MEMORY COMMANDS

Read Scratchpad Reads the entire scratchpad

including the CRC byte. BEh DS18S20 transmits up to 9 data

bytes to master. 2

Write Scratchpad Writes data into scratchpad

bytes 2 and 3 (TH and TL). 4Eh Master transmits 2 data bytes to

DS18S20. 3

Copy Scratchpad Copies TH and TL data from the

scratchpad to EEPROM. 48h None 1

Recall E2Recalls TH and TL data from

EEPROM to the scratchpad. B8h DS18S20 transmits recall status to

master.

Read Power

Supply

Signals DS18S20 power supply

mode to the master. B4h DS18S20 transmits supply status to

master.

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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 DS18S20 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 DS18S20 section. If the DS18S20 is pow-

ered by an external supply, the master can issue read-

time slots after the Convert T command and the DS18S20

will respond by transmitting 0 while the temperature con-

version is in progress and 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 2 bytes of data

to the DS18S20’s scratchpad. The first byte is written into

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

byte is written into the TL register (byte 3 of the scratch-

pad). Data must be transmitted least significant bit first.

Both 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.

Copy Scratchpad [48h]

This command copies the contents of the scratchpad TH

and TL registers (bytes 2 and 3) 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 DS18S20 section.

Recall E2 [B8h]

This command recalls the alarm trigger values (TH and

TL) from EEPROM and places the data in bytes 2 and

3, respectively, in the scratchpad memory. The master

device can issue read-time slots following the Recall E2

command and the DS18S20 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 DS18S20s on the bus

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

site powered DS18S20s will pull the bus low, and exter-

nally powered DS18S20s will let the bus remain high. See

the Powering The DS18S20 section for usage information

for this command.

1-Wire Signaling

The DS18S20 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. All these signals, with

the exception of the presence pulse, are initiated by the

bus master.

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Initialization Procedure—Reset And

Presence Pulses

All communication with the DS18S20 begins with an ini-

tialization sequence that consists of a reset pulse from the

master followed by a presence pulse from the DS18S20.

This is illustrated in Figure 12. When the DS18S20 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 DS18S20 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 DS18S20 during write

time slots and reads data from the DS18S20 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 DS18S20 and a Write

0 time slot to write a logic 0 to the DS18S20. 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 13).

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 DS18S20 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 DS18S20. If the

line is low, a 0 is written to the DS18S20.

Figure 12. Initialization Timing

LINE TYPE LEGEND

BUS MASTER PULLING LOW

DS18S20 PULLING LOW

RESISTOR PULLUP

GND

1-Wire BUS

DS18S20

WAITS 15-60µs

DS18S20 Tx

PRESENCE PULSE

60-240µs

MASTER Rx

480µs MINIMUM

MASTER Tx RESET PULSE

480µs MINIMUM

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Figure 13. Read/Write Time Slot Timing Diagram

GND

1-Wire BUS

1µs < T

REC

< ∞

MIN

> 1µs

MASTER WRITE “0” SLOT MASTER WRITE “1” SLOT

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

MASTER SAMPLES MASTER SAMPLES

START

OF SLOT

START

OF SLOT

DS18S20 SAMPLES

> 1µs

LINE TYPE LEGEND

BUS MASTER PULLING LOW

60µs < Tx “0” < 120µs

TYP MAX

30µS

15µS

15µS 30µS

15µS

MIN TYP MAX

DS18S20 SAMPLES

1µs < T

REC

< ∞

GND

1-Wire BUS

15µs 45µs

> 1µs

15µs

RESISTOR PULLUP

DS18S20 PULLING LOW

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Read-Time Slots

The DS18S20 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 DS18S20 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 DS18S20 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 13). After the master initiates the

read-time slot, the DS18S20 will begin transmitting a 1

or 0 on bus. The DS18S20 transmits a 1 by leaving the

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

transmitting a 0, the DS18S20 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 DS18S20 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 14 illustrates that the sum of TINIT, TRC, and

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

Figure 15 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 14. Detailed Master Read 1 Timing

Figure 15. Recommended Master Read 1 Timing

GND

1-Wire BUS

MASTER SAMPLES

VIH OF MASTER

INT

> 1µs T

15µs

LINE TYPE LEGEND

BUS MASTER PULLING LOW

RESISTOR PULLUP

GND

1-Wire BUS VIH OF MASTER

SMALL

MASTER SAMPLES

INT

SMALL

15µs

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Figure 16. ROM Commands Flowchart

CCh

SKIP ROM

COMMAND

MASTER Tx RESET PULSE

DS18S20 Tx PRESENCE PULSE

MASTER Tx ROM COMMAND

33h

READ ROM

COMMAND

55h

MATCH ROM

COMMAND

F0h

SEARCH ROM

COMMAND

ECh

ALARM SEARCH

COMMAND

MASTER Tx

BIT 0

DS18S20 Tx BIT 0

MASTER Tx BIT 0

BIT 0

MATCH?

MASTER Tx

BIT 1

MATCH?

BIT 63

MATCH?

MASTER Tx

BIT 63

YY Y

DS18S20 Tx BIT 1

MASTER Tx BIT 1

DS18S20 T BIT 63

DS18S20 Tx BIT 63

MASTER Tx BIT 63

BIT 0

MATCH?

BIT 1

MATCH?

BIT 63

MATCH?

DS18S20 Tx

FAMILY CODE

1 BYTE

DS18S20 Tx

SERIAL NUMBER

6 BYTES

DS18S20 Tx

CRC BYTE

DS18S20 Tx BIT 0

MASTER Tx BIT 0

DEVICE(S)

WITH ALARM

FLAG SET?

INITIALIZATION

SEQUENCE

MASTER Tx FUNCTION

COMMAND (FIGURE 17)

N N

NNN

DS18S20 Tx BIT 1

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Figure 17. DS18S20 Function Commands Flowchart

MASTER Tx

FUNCTION

COMMAND

44h

CONVERT

TEMPERATURE

DS18S20 BEGINS

CONVERSION

DEVICE

CONVERTING

TEMPERATURE

MASTER

Rx “0s”

MASTER

Rx “1s”

MASTER ENABLES

STRONG PULLUP ON DQ

DS18S20 CONVERTS

TEMPERATURE

MASTER DISABLES

STRONG PULLUP

48h

COPY

SCRATCHPAD

PARASITE

POWER

MASTER ENABLES

STRONG PULL- UP ON DQ

DATA COPIED FROM

SCRATCHPAD TO EEPROM

MASTER DISABLES

STRONG PULLUP

MASTER

Rx “0s”

COPY IN

PROGRESS

MASTER

Rx “1s”

RETURN TO INITIALIZATION SEQUENCE

(FIGURE 16) FOR NEXT TRANSACTION

B4h READ

POWER SUPPLY

PARASITE

POWERED

MASTER

Rx “1s”

MASTER

Rx “0s”

MASTER Tx T

BYTE

TO SCRATCHPAD

4Eh

WRITE

SCRATCHPAD

MASTER Tx T

BYTE

TO SCRATCHPAD

BEh

READ

SCRATCH PAD

HAVE 8 BYTES

BEEN READ

MASTER

Tx RESET

MASTER Rx DATA BYTE

FROM SCRATCHPAD

MASTER Rx SCRATCHPAD

CRC BYTE

MASTER

Rx “1s”

NB8h

RECALL E

MASTER BEGINS DATA

RECALL FROM E

PROM

DEVICE

BUSY RECALLING

DATA

MASTER

Rx “0s”

PARASITE

POWER

Y Y

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Ds18S20 Operation Example 1

In this example there are multiple DS18S20s on the bus and they are using parasite power. The bus master initiates a

temperature conversion in a specific DS18S20 and then reads its scratchpad and recalculates the CRC to verify the data.

DS18S20 Operation Example 2

In this example there is only one DS18S20 on the bus and it is using parasite power. The master writes to the TH and

TL registers in the DS18S20 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 DS18S20s respond with presence pulse.

Tx 55h Master issues Match ROM command.

Tx 64-bit ROM code Master sends DS18S20 ROM code.

Tx 44h Master issues Convert T command.

Tx 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 DS18S20s respond with presence pulse.

Tx 55h Master issues Match ROM command.

Tx 64-bit ROM code Master sends DS18S20 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 DS18S20 responds with presence pulse.

Tx CCh Master issues Skip ROM command.

Tx 4Eh Master issues Write Scratchpad command.

Tx 2 data bytes Master sends two data bytes to scratchpad (TH and TL)

Tx Reset Master issues reset pulse.

Rx Presence DS18S20 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 DS18S20 responds with presence pulse.

Tx CCh Master issues Skip ROM command.

Tx 48h Master issues Copy Scratchpad command.

Tx DQ line held high by

strong pullup

Master applies strong pullup to DQ for at least 10ms while copy

operation is in progress.

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DS18S20 Operation Example 3

In this example there is only one DS18S20 on the bus and it is using parasite power. The bus master initiates a tempera-

ture conversion then reads the DS18S20 scratchpad and calculates a higher resolution result using the data from the

temperature, COUNT REMAIN and COUNT PER °C registers.

MASTER MODE DATA (LSB FIRST) COMMENTS

Tx Reset Master issues reset pulse.

Tx Presence DS18S20 responds with presence pulse.

Tx CCh Master issues Skip ROM command.

Tx 44h Master issues Convert T command.

Tx 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 DS18S20 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. The master also calculates

the TEMP_READ value and stores the contents of the COUNT REMAIN and

Count Per °C registers.

Tx Reset Master issues reset pulse.

Rx Presence DS18S20 responds with presence pulse.

— — CPU calculates extended resolution temperature using the equation in

the Operation—Measuring Temperature section.

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+Denotes a lead(Pb)-free/RoHS-compliant package. A “+”

appears on the top mark of lead(Pb)-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

DS18S20+ –55°C to +125°C 3 TO-92

DS18S20+T&R –55°C to +125°C 3 TO-92 (2000 Piece)

DS18S20-SL+T&R –55°C to +125°C 3 TO-92 (2000 Piece)*

DS18S20Z –55°C to +125°C 8 SO

DS18S20Z+ –55°C to +125°C 8 SO

DS18S20Z/T&R –55°C to +125°C 8 SO (2500 Piece)

DS18S20Z+T&R –55°C to +125°C 8 SO (2500 Piece)

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

8 SO S8-2 21-0041 90-0096

3 TO-92

(straight leads) Q3-1 21-0248 —

3 TO-92

(formed leads) Q3-4 21-0250 —

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Ordering Information Package Information

For the latest package outline information and land patterns

(footprints), go to www.maximintegrated.com/packages. Note

that a “+”, “#”, or “-” in the package code indicates RoHS status

only. Package drawings may show a different suffix character, but

the drawing pertains to the package regardless of RoHS status.

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 4/08

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

1 8/10

Removed the Top Mark column from the Ordering Information table; added the

continuous power dissipation and lead and soldering temperatures to the Absolute

Maximum Ratings section

2, 20

2 1/15 Updated General Description and Benets and Features section and added

Applications section 1

3 4/15 Revised Pin Conguration and Ordering Information 1, 20

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.

│

DS18S20 High-Precision 1-Wire Digital Thermometer

Revision History

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