DS18S20_技术文档

DS18S20

High-Precision 1-Wire Digital Thermometer

FEATURES

PIN CONFIGURATIONS

. Unique 1-Wire^®Interface Requires Only One

Port Pin for Communication

MAXIM

DS1820

. Each Device has a Unique 64-Bit Serial Code

Stored in an On-Board ROM

1 2 3

. Multidrop Capability Simplifies Distributed

Temperature Sensing Applications

. Requires No External Components

. Can Be Powered from Data Line. Power

Supply Range is 3.0V to 5.5V

8

7

N.C.

V_DD

N.C.

GND

1

2

3

4

. Measures Temperatures from -55°C to

+125°C (-67°F to +257°F)

6

5

DQ

. ±0.5°C Accuracy from -10°C to +85°C

. 9-Bit Thermometer Resolution

. Converts Temperature in 750ms (max)

. User-Definable Nonvolatile (NV) Alarm

Settings

SO (150 mils)

(DS18S20Z)

. Alarm Search Command Identifies and

Addresses Devices Whose Temperature is

Outside Programmed Limits (Temperature

Alarm Condition)

1

2 3

(BOTTOM VIEW)

TO-92

.

Applications Include Thermostatic Controls,

Industrial Systems, Consumer Products,

Thermometers, or Any Thermally Sensitive

System

(DS18S20)

DESCRIPTION

The DS18S20 digital thermometer provides 9-bit Celsius temperature measurements and has an alarm

function with nonvolatile user-programmable upper and lower trigger 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. It has an operating temperature range of –55°C to +125°C

and is accurate to ±0.5°C over the range of –10°C to +85°C. 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.

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

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

19-5474; Rev 8/10

DS18S20

ORDERING INFORMATION

PART

DS18S20

TEMP RANGE

–55°C to +125°C

PIN-PACKAGE

3 TO-92

3 TO-92 (2000 Piece)

3 TO-92 (2000 Piece)*

8 SO

DS18S20+

DS18S20/T&R

DS18S20+T&R

DS18S20-SL/T&R

DS18S20-SL+T&R

DS18S20Z

DS18S20Z+

DS18S20Z/T&R

DS18S20Z+T&R

8 SO

8 SO (2500 Piece)

+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.

PIN DESCRIPTION

NAME

FUNCTION

TO-92

SO

1

5

GND

Ground

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.)

2

4

DQ

Optional V_DD. V_DDmust be grounded for operation in parasite

power mode.

3

V_DD

1, 2, 6, 7,

8

—

N.C.

No Connection

OVERVIEW

Figure 1 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 register that stores the digital output from the temperature sensor. In addition, the scratchpad

provides access to the 1-byte upper and lower alarm trigger registers (T_Hand T_L). The T_Hand T_Lregisters

are nonvolatile (EEPROM), so they will retain data when the device is powered down.

The DS18S20 uses Maxim’s exclusive 1-Wire bus protocol that implements bus communication using

one control signal. The control line requires a weak pullup resistor since all devices are linked to the bus

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 supplied through the 1-Wire pullup resistor via the DQ pin when the bus is high. The high bus

signal also charges an internal capacitor (C_PP), 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 V_DD.

2 of 23

DS18S20

Figure 1. DS18S20 Block Diagram

V_PU

PARASITE POWER

4.7k

MEMORY CONTROL

LOGIC

DS18S20

CIRCUIT

DQ

TEMPERATURE SENSOR

64-BIT ROM

AND

INTERNAL V_DD

1-Wire PORT

ALARM HIGH TRIGGER (T_H)

REGISTER (EEPROM)

GND

SCRATCHPAD

C_PP

ALARM LOW TRIGGER (T_L)

REGISTER (EEPROM)

POWER-

SUPPLY

SENSE

V_DD

8-BIT CRC GENERATOR

OPERATION—MEASURING TEMPERATURE

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

temperature conversion is in progress and 1 when the conversion 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.

The DS18S20 output data is calibrated in degrees centigrade; 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 number in the temperature register (see Figure 2). 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 2). The extended resolution temperature can then be

calculated using the following equation:

COUNT _ PER _C −COUNT _ REMAIN

TEMPERATURE = TEMP _ READ − 0.25 +

COUNT _ PER _C

3 of 23

DS18S20

Figure 2. Temperature Register Format

BIT 7

2⁶

BIT 6

2⁵

BIT 5

2⁴

BIT 4

2³

BIT 3

2²

BIT 2

2¹

BIT 1

2⁰

BIT 0

2^-1

LS BYTE

BIT 15

S

BIT 14

S

BIT 13

S

BIT 12

S

BIT 11

S

BIT 10

S

BIT 9

S

BIT 8

S

MS BYTE

S = SIGN

Table 1. Temperature/Data Relationship

TEMPERATURE

DIGITAL OUTPUT

(BINARY)

DIGITAL OUTPUT

(HEX)

(°C)

+85.0*

+25.0

+0.5

0

-0.5

-25.0

-55.0

0000 0000 1010 1010

0000 0000 0011 0010

0000 0000 0000 0001

0000 0000 0000 0000

1111 1111 1111 1111

1111 1111 1100 1110

1111 1111 1001 0010

00AAh

0032h

0001h

0000h

FFFFh

FFCEh

FF92h

*The power-on reset value of the temperature register is +85°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 T_Hand T_Lregisters (see Figure 3).

The sign bit (S) indicates if the value is positive or negative: for positive numbers S = 0 and for negative

numbers S = 1. The T_Hand T_Lregisters are nonvolatile (EEPROM) so they will retain data when the

device is powered down. T_Hand T_Lcan be accessed through bytes 2 and 3 of the scratchpad as explained

in the Memory section.

Figure 3. T and T Register Format

H

L

BIT 7

BIT 6

2⁶

BIT 5

2⁵

BIT 4

2⁵

BIT 3

2⁵

BIT 2

2²

BIT 1

2¹

BIT 0

2⁰

S

Only bits 8 through 1 of the temperature register are used in the T_Hand T_Lcomparison since T_Hand T_L

are 8-bit registers. If the measured temperature is lower than or equal to T_Lor higher than T_H, 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.

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 T_Hor T_Lsettings have changed, another temperature conversion should be done to validate the alarm

condition.

4 of 23

DS18S20

POWERING THE DS18S20

The DS18S20 can be powered by an external supply on the V_DDpin, 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 applications that require remote temperature sensing or those with space constraints.

Figure 1 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 (C_PP) to provide power when the bus is

low. When the DS18S20 is used in parasite power mode, the V_DDpin must be connected to ground.

In parasite power mode, the 1-Wire bus and C_PPcan provide sufficient current to the DS18S20 for most

operations as long as the specified timing and voltage requirements 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 C_PP. 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 4. The 1-Wire

bus must be switched to the strong pullup within 10µs (max) after a Convert T [44h] or Copy Scratchpad

[48h] command is issued, and the bus must be held high by the pullup for the duration of the conversion

(t_CONV) or data transfer (t_WR= 10ms). No other activity can take place on the 1-Wire bus while the pullup

is enabled.

The DS18S20 can also be powered by the conventional method of connecting an external power supply to

the V_DDpin, as shown in Figure 5. 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 temperature conversion time.

The use of parasite power is not recommended for temperatures above 100°C since the DS18S20 may not

be able to sustain communications due to the higher leakage 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 powered by external supplies. The master needs this information 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 followed 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.

5 of 23

DS18S20

Figure 4. Supplying the Parasite-Powered DS18S20 During Temperature Conversions

V_PU

DS18S20

GND

DQ V_DD

V_PU

µP

4.7k

TO OTHER

1-WIRE DEVICES

1-Wire BUS

Figure 5. Powering the DS18S20 with an External Supply

V_DD(EXTERNAL SUPPLY)

TO OTHER

DS18S20

V_PU

µP

GND

DQ V_DD

4.7k

1-Wire BUS

1-WIRE DEVICES

64-BIT LASERED ROM CODE

Each DS18S20 contains a unique 64-bit code (see Figure 6) 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.

Figure 6. 64-Bit Lasered ROM Code

8-BIT CRC

48-BIT SERIAL NUMBER

8-BIT FAMILY CODE (10h)

MSB LSB

MSB

LSB MSB

LSB

6 of 23

DS18S20

MEMORY

The DS18S20’s memory is organized as shown in Figure 7. The memory consists of an SRAM

scratchpad with nonvolatile EEPROM storage for the high and low alarm trigger registers (T_Hand T_L).

Note that if the DS18S20 alarm function is not used, the T_Hand T_Lregisters can serve as general-purpose

memory. All memory 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 T_Hand T_Lregisters. 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 significant bit of byte 2. To verify data

integrity, the scratchpad can be read (using the Read Scratchpad [BEh] command) after the data is

written. When reading the scratchpad, data is transferred over the 1-Wire bus starting with the least

significant bit of byte 0. To transfer the T_Hand T_Ldata 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 scratchpad 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 E²command 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.

Figure 7. DS18S20 Memory Map

SCRATCHPAD

(POWER-UP STATE)

Byte 0 Temperature LSB (AAh)

(85°C)

Byte 1 Temperature MSB (00h)

Byte 2 T_HRegister or User Byte 1*

Byte 3 T_LRegister or User Byte 2*

Byte 4 Reserved (FFh)

EEPROM

T_HRegister or User Byte 1

T_LRegister or User Byte 2

Byte 5 Reserved (FFh)

Byte 6 COUNT REMAIN (0Ch)

Byte 7 COUNT PER °C (10h)

Byte 8 CRC*

*Power-up state depends on value(s) stored in EEPROM.

7 of 23

DS18S20

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 changes when the data in the scratchpad changes. The CRCs provide the bus

master with a method of data validation when data is read from the 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 calculated CRC matches the read CRC, the data has been received error free. The comparison of CRC

values and the decision to continue with an operation are determined entirely by the bus master. There is

no circuitry inside the DS18S20 that prevents a command sequence from proceeding 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

polynomial generator shown in Figure 8. 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

iButton Products.

Figure 8. CRC Generator

INPUT

XOR

(MSB)

(LSB)

8 of 23

DS18S20

1-WIRE BUS SYSTEM

The 1-Wire bus system uses a single bus master to control one or more slave devices. The DS18S20 is

always a slave. When there is only one slave on the bus, the system 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 CONFIGURATION

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 9.

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.

Figure 9. Hardware Configuration

V_PU

DS18S20 1-Wire PORT

DQ

4.7k

1-Wire BUS

Rx

Tx

5μA

TYP

TX

100Ω

MOSFET

Rx = RECEIVE

Tx = TRANSMIT

9 of 23

DS18S20

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 initialization 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 presence 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 commands, 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 14.

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 command (see below)

can be used in place of the Search ROM process. For a detailed explanation of the Search ROM

procedure, refer to the iButton^®Book of Standards at www.maxim-ic.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 procedure. 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.

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

10 of 23

DS18S20

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 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 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 transaction sequence. See the Operation—Alarm Signaling section

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

communicate, 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 illustrated by the flowchart in Figure 15.

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 scratchpad 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 (t_CONV) as described in the Powering the DS18S20 section. If the DS18S20 is powered 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 conversion 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 T_Hregister (byte 2 of the scratchpad), and the second byte is written into the T_Lregister

(byte 3 of the scratchpad). 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 significant 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.

11 of 23

DS18S20

COPY SCRATCHPAD [48h]

This command copies the contents of the scratchpad T_Hand T_Lregisters (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 (T_Hand T_L) 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 E²command 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, parasite powered DS18S20s will pull the bus low,

and externally powered DS18S20s will let the bus remain high. See the Powering the DS18S20 section

for usage information for this command.

Table 2. DS18S20 Function Command Set

1-Wire BUS ACTIVITY

COMMAND

DESCRIPTION

PROTOCOL

AFTER COMMAND IS

ISSUED

NOTES

TEMPERATURE CONVERSION COMMANDS

Convert T

Initiates temperature

conversion.

DS18S20 transmits conversion

status to master (not applicable

for parasite-powered

44h

1

DS18S20s).

MEMORY COMMANDS

Read

Scratchpad

Reads the entire

scratchpad including the

CRC byte.

Writes data into

scratchpad bytes 2 and 3

(T_Hand T_L).

Copies T_Hand T_Ldata

from the scratchpad to

EEPROM.

Recalls T_Hand T_Ldata

from EEPROM to the

scratchpad.

Signals DS18S20 power

supply mode to the

master.

DS18S20 transmits up to 9

data bytes to master.

BEh

4Eh

48h

B8h

B4h

2

3

1

Write

Scratchpad

Master transmits 2 data bytes

to DS18S20.

Copy

Scratchpad

None

Recall E²

DS18S20 transmits recall

status to master.

Read Power

Supply

DS18S20 transmits supply

status to master.

For parasite-powered DS18S20s, the master must enable a strong pullup on the 1-Wire bus during temperature

conversions and copies from the scratchpad to EEPROM. No other bus activity may take place during this time.

The master can interrupt the transmission of data at any time by issuing a reset.

Note 1:

Note 2:

Note 3:

Both bytes must be written before a reset is issued.

12 of 23

DS18S20

1-WIRE SIGNALING

The DS18S20 uses a strict 1-Wire communication protocol 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.

INITIALIZATION PROCEDURE—RESET AND PRESENCE PULSES

All communication with the DS18S20 begins with an initialization sequence that consists of a reset pulse

from the master followed by a presence pulse from the DS18S20. This is illustrated in Figure 10. 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 transmits (T_X) 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 (R_X).

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 pulling the 1-Wire bus low

for 60µs to 240µs.

Figure 10. Initialization Timing

MASTER T_XRESET PULSE

MASTER R_X

480µs minimum

DS18S20 T_X

presence pulse

DS18S20

waits 15-60 µs

60-240 µs

V_PU

1-WIRE BUS

GND

LINE TYPE LEGEND

Bus master pulling low

DS18S20 pulling low

Resistor pullup

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 11).

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.

13 of 23

DS18S20

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 requested data. In addition, the master can

generate read-time slots after issuing Convert T [44h] or Recall E²[B8h] commands 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 11). 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 12 illustrates that the sum of T_INIT, T_RC, and T_SAMPLEmust be less than 15µs for a read-time slot.

Figure 13 shows that system timing margin is maximized by keeping T_INITand T_RCas short as possible

and by locating the master sample time during read-time slots towards the end of the 15µs period.

Figure 11. Read/Write Time Slot Timing Diagram

START

OF SLOT

START

OF SLOT

MASTER WRITE “0” SLOT

MASTER WRITE “1” SLOT

1µs < T_REC< ∞

60µs < T_X“0” < 120µs

> 1µs

V_PU

1-WIRE BUS

GND

DS18S20 Samples

MIN

TYP

MAX

MIN

TYP

MAX

15µs

30µs

MASTER READ “0” SLOT

MASTER READ “1” SLOT

1µs < T_REC< ∞

V_PU

1-WIRE BUS

GND

> 1 µs

Master samples

> 1µs

15µs

45µs

15µs

LINE TYPE LEGEND

Bus master pulling low

DS18S20 pulling low

Resistor pullup

14 of 23

DS18S20

Figure 12. Detailed Master Read 1 Timing

V_PU

VIH of Master

1-WIRE BUS

GND

T_INT> 1µs

T_RC

Master samples

15µs

Figure 13. Recommended Master Read 1 Timing

V_PU

VIH of Master

1-WIRE BUS

GND

Master samples

T_INT

= T_RC=

small small

15µs

LINE TYPE LEGEND

Bus master pulling low

Resistor pullup

15 of 23

DS18S20

Figure 14. ROM Commands Flowchart

Initialization

Sequence

MASTER T_X

RESET PULSE

DS18S20 T_X

PRESENCE

PULSE

MASTER T_XROM

COMMAND

CCh

SKIP ROM

COMMAND

33h

READ ROM

COMMAND

55h

MATCH ROM

COMMAND

F0h

SEARCH ROM

COMMAND

ECh

N

ALARM SEARCH

COMMAND

Y

MASTER T_X

BIT 0

DS18S20 T_XBIT 0

MASTER T_XBIT 0

DS18S20 T_XBIT 0

MASTER T_XBIT 0

DS18S20 T_X

FAMILY CODE

1 BYTE

N

DEVICE(S)

WITH ALARM

FLAG SET?

N

BIT 0

MATCH?

BIT 0

MATCH?

DS18S20 T_X

SERIAL NUMBER

6 BYTES

Y

DS18S20 T_XBIT 1

MASTER T_XBIT 1

MASTER T_X

BIT 1

DS18S20 T_X

CRC BYTE

N

BIT 1

MATCH?

Y

DS18S20 T_XBIT 63

MASTER T_X

BIT 63

DS18S20 T_XBIT 63

MASTER T_XBIT 63

N

BIT 63

MATCH?

BIT 63

MATCH?

Y

MASTER T_X

FUNCTION

COMMAND

(FIGURE 15)

16 of 23

DS18S20

Figure 15. DS18S20 Function Commands Flowchart

44h

48h

COPY

SCRATCHPAD

N

MASTER T_X

FUNCTION

COMMAND

CONVERT

TEMPERATURE

?

Y

N

PARASITE

POWER

?

PARASITE

POWER

?

MASTER ENABLES

STRONG PULL-UP ON DQ

DS18S20 BEGINS

CONVERSION

MASTER ENABLES

STRONG PULLUP ON DQ

DATA COPIED FROM

SCRATCHPAD TO EEPROM

DS18S20 CONVERTS

TEMPERATURE

N

COPY IN

PROGRESS

?

DEVICE

CONVERTING

TEMPERATURE

?

N

MASTER DISABLES

STRONG PULLUP

Y

MASTER DISABLES

STRONG PULLUP

Y

MASTER

R_X“0s”

MASTER

R_X“1s”

MASTER

R_X“0s”

MASTER

R_X“1s”

B4h

READ

POWER SUPPLY

BEh

READ

SCRATCHPAD

4Eh

WRITE

SCRATCHPAD

?

N

B8h

RECALL E²

?

N

?

Y

MASTER T_XT_HBYTE

TO SCRATCHPAD

MASTER R_XDATA BYTE

FROM SCRATCHPAD

N

Y

PARASITE

POWERED

?

MASTER BEGINS DATA

RECALL FROM E²PROM

MASTER T_XT_LBYTE

TO SCRATCHPAD

Y

MASTER

R_X“1s”

MASTER

R_X“0s”

MASTER

T_XRESET

?

DEVICE

BUSY RECALLING

N

DATA

?

N

Y

HAVE 8 BYTES

BEEN READ

?

MASTER

R_X“0s”

MASTER

R_X“1s”

Y

MASTER R_XSCRATCHPAD

CRC BYTE

RETURN TO INITIALIZATION

SEQUENCE (FIGURE 14) FOR

NEXT TRANSACTION

17 of 23

DS18S20

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.

MASTER MODE

DATA (LSB FIRST)

Reset

COMMENTS

Master issues reset pulse.

DS18S20s respond with presence pulse.

Master issues Match ROM command.

Master sends DS18S20 ROM code.

Master issues Convert T command.

Tx

Rx

Tx

Presence

55h

64-bit ROM code

44h

DQ line held high by

strong pullup

Reset

Master applies strong pullup to DQ for the duration of the

conversion (t_CONV).

Master issues reset pulse.

DS18S20s respond with presence pulse.

Master issues Match ROM command.

Master sends DS18S20 ROM code.

Master issues Read Scratchpad command.

Master reads entire scratchpad including CRC. The master

then recalculates the CRC of the first 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

Rx

Tx

Presence

55h

64-bit ROM code

BEh

Rx

9 data bytes

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 T_Hand T_Lregisters 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

Master issues reset pulse.

DS18S20 responds with presence pulse.

Master issues Skip ROM command.

Master issues Write Scratchpad command.

Master sends two data bytes to scratchpad (T_Hand T_L)

Master issues reset pulse.

DS18S20 responds with presence pulse.

Master issues Skip ROM command.

Master issues Read Scratchpad command.

Master reads entire scratchpad including CRC. The master

then recalculates the CRC of the first 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

Rx

Tx

Rx

Tx

Reset

Presence

CCh

4Eh

2 data bytes

Reset

Presence

CCh

BEh

Rx

9 data bytes

Tx

Rx

Tx

Reset

Presence

CCh

Master issues reset pulse.

DS18S20 responds with presence pulse.

Master issues Skip ROM command.

Master issues Copy Scratchpad command.

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

copy operation is in progress.

48h

DQ line held high by

strong pullup

Tx

18 of 23

DS18S20

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 temperature 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

Master issues reset pulse.

DS18S20 responds with presence pulse.

Master issues Skip ROM command.

Master issues Convert T command.

Tx

Reset

Presence

CCh

44h

DQ line held high by

strong pullup

Reset

Master applies strong pullup to DQ for the duration of the

conversion (t_CONV).

Master issues reset pulse.

DS18S20 responds with presence pulse.

Master issues Skip ROM command.

Master issues Read Scratchpad command.

Master reads entire scratchpad including CRC. The master

then recalculates the CRC of the first 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

Rx

Tx

Presence

CCh

BEh

Rx

9 data bytes

Tx

Rx

Reset

Presence

Master issues reset pulse.

DS18S20 responds with presence pulse.

CPU calculates extended resolution temperature using the

equation in the Operation—Measuring Temperature section.

—

19 of 23

DS18S20

ABSOLUTE MAXIMUM RATINGS

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

Continuous Power Dissipation (T_A= +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

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

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

PARAMETER

Supply Voltage

Pullup Supply

Voltage

SYMBOL

CONDITIONS

Local Power

Parasite Power

Local Power

-10°C to +85°C

-55°C to +125°C

MIN

+3.0

TYP

MAX

+5.5

V_DD

±0.5

±2

UNITS NOTES

V_DD

V

1

V_PU

V

1, 2

Thermometer Error

Input Logic-Low

t_ERR

V_IL

°C

V

3

-0.3

+0.8

1, 4, 5

The lower of

Local Power

+2.2

5.5

or

Input Logic-High

V_IH

V

1, 6

Parasite Power

V_I/O= 0.4V

+3.0

4.0

V_DD+ 0.3

Sink Current

Standby Current

Active Current

DQ Input Current

Drift

I_L

mA

nA

mA

µA

°C

1

7, 8

9

10

11

I_DDS

I_DD

I_DQ

750

1

5

1000

1.5

V_DD= 5V

±0.2

NOTES:

1) All voltages are referenced to ground.

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

the pullup is equal to V_PU. In order to meet the V_IHspec 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:

V_{PU_ACTUAL}= V_{PU_IDEAL}+ V_TRANSISTOR.

3) See typical performance curve in Figure 16.

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

5) To guarantee a presence pulse under low voltage parasite power conditions, V_ILMAXmay have to be reduced to

as low as 0.5V.

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

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

8) To minimize I_DDS, DQ should be within the following ranges: GND ≤ DQ ≤ GND + 0.3V or

V_DD– 0.3V ≤ DQ ≤ V_DD.

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

10) DQ line is high (“high-Z” state).

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

20 of 23

DS18S20

AC ELECTRICAL CHARACTERISTICS—NV MEMORY

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

PARAMETER

NV Write Cycle Time

EEPROM Writes

SYMBOL

CONDITIONS

MIN

TYP

2

MAX

10

UNITS

ms

writes

years

t_WR

N_EEWR

t_EEDR

-55°C to +55°C

50k

10

EEPROM Data Retention

AC ELECTRICAL CHARACTERISTICS

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

PARAMETER

Temperature Conversion

Time

SYMBOL

CONDITIONS

MIN TYP MAX UNITS NOTES

t_CONV

750

ms

1

Start Convert T

Command Issued

Time to Strong Pullup On

t_SPON

10

µs

Time Slot

t_SLOT

t_REC

t_LOW0

t_LOW1

t_RDV

t_RSTH

t_RSTL

t_PDHIGH

t_PDLOW

C_IN/OUT

60

1

60

1

120

1

1, 2

1

µs

pF

Recovery Time

Write 0 Low Time

Write 1 Low Time

Read Data Valid

Reset Time High

Reset Time Low

Presence-Detect High

Presence-Detect Low

Capacitance

120

15

480

15

60

240

25

60

1

NOTES:

1) See the timing diagrams in Figure 17.

2) Under parasite power, if t_RSTL> 960µs, a power-on reset may occur.

Figure 16. Typical Performance Curve

DS18S20 Typical Error Curve

0.5

0.4

+3s Error

0.3

0.2

0.1

0

10

20

30

40

50

60

70

-0.1

-0.2

-0.3

-0.4

-0.5

Mean Error

-3s Error

Temperature (°C)

21 of 23

DS18S20

Figure 17. Timing Diagrams

PACKAGE INFORMATION

For the latest package outline information and land patterns, go to www.maxim-ic.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.

PACKAGE TYPE

8 SO

PACKAGE CODE

OUTLINE NO.

21-0041

LAND PATTERN NO.

90-0096

S8-2

3 TO-92

(straight leads)

3 TO-92

(formed leads)

Q3-1

Q3-4

—

21-0248

21-0250

22 of 23

DS18S20

REVISION HISTORY

REVISION

PAGES

CHANGED

DESCRIPTION

DATE

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

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

042208

8/10

2

2, 20

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.

Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical

Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.

23

The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.

Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000

©

2010 Maxim Integrated


型号：	DS18S20
厂家：	MAXIM INTEGRATED PRODUCTS
描述：	High-Precision 1-Wire Digital Thermometer 高精度的1-Wire数字温度计传感器换能器输出元件
文件：	总23页 (文件大小：317K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

DS18S20 [MAXIM]

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