DS18B20P - Hytronics - Datasheet.Live

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FEATURES

 Unique 1-WireTM interface requires only one

port pin for communication

 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

 Zero standby power required

 Measures temperatures from -55°C to

+125°C. Fahrenheit equivalent is -67°F to

+257°F

 ±0.5°C accuracy from -10°C to +85°C

 Thermometer resolution is programmable

from 9 to 12 bits

 Converts 12-bit temperature to digital word in

750 ms (max.)

 User-definable, nonvolatile temperature alarm

settings

 Alarm search command identifies and

addresses devices whose temperature is

outside of programmed limits (temperature

alarm condition)

 Applications include thermostatic controls,

industrial systems, consumer products,

thermometers, or any thermally sensitive

system

PIN ASSIGNMENT

PIN DESCRIPTION

GND - Ground

DQ - Data In/Out

VDD - Power Supply Voltage

NC - No Connect

DESCRIPTION

The DS18B20 Digital Thermometer provides 9 to 12-bit (configurable) temperature readings which

indicate the temperature of the device.

Information is sent to/from the DS18B20 over a 1-Wire interface, so that only one wire (and ground)

needs to be connected from a central microprocessor to a DS18B20. Power for reading, writing, and

performing temperature conversions can be derived from the data line itself with no need for an external

power source.

Because each DS18B20 contains a unique silicon serial number, multiple DS18B20s can exist on the

same 1-Wire bus. This allows for placing temperature sensors in many different places. Applications

where this feature is useful include HVAC environmental controls, sensin g tempe ratures inside buildings,

equipment or machinery, and process monitoring and control.

DS18B20

Programmable Resolution

1-Wire Digital Thermomete

www.dalsemi.com

PRELIMINARY

DALLAS

DS1820

1 2 3

GND

1 2 3

BOTTOM VIEW

DS18B20 TO-92

PACKAGE

VDD

DS18B20Z

8-PIN SOIC

(

150-MIL

)

DS18B20P

TSOC

VDD

GND NC

DS18B20

2 of 26

DETAILED PIN DESCRIPTION Table 1

TSOC PIN

8PIN SOIC PIN

TO92 SYMBOL DESCRIPTION

1 5 1 GND Ground.

242DQData Input/Output pin. For 1-Wire operation: Open

drain. (See “Parasite Power” section.)

333V

DD Optional VDD pin. See “Parasite Power” section for

details of connection. VDD must be grounded for

operation in parasite power mode.

DS18B20Z (8-pin SOIC) and DS18P20P (TSOC): All pins not specified in this table are not to be

connected.

OVERVIEW

The block diagram of Figure 1 shows the major components of the DS18B20. The DS18B20 has four

main data components: 1) 64-bit lasered ROM, 2) temperature sensor, 3) nonvolatile temperature alarm

triggers TH and TL, and 4) a configuration register. The device derives its power from the 1-Wire

communication line by storing energy on an internal capacitor during periods of time when the signal line

is high and continues to operate off this power source during the low times of the 1-Wire line until it

returns high to replenish the parasite (capacitor) supply. As an alternative, the DS18B20 may also be

powered from an external 3V - 5.5V supply.

Communication to the DS18B20 is via a 1-Wire port. With the 1-Wire port, the memory and control

functions will not be available before the ROM function protocol has been established. The master must

first provide one of five ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4)

Skip ROM, or 5) Alarm Search. These commands operate on the 64-bit lasered ROM portion of each

device and can single out a specific device if many are present on the 1-Wire line as well as indicate to

the bus master how many and what types of devices are present. After a ROM function sequence has been

successfully executed, the memor y and control functions are accessible and the master ma y then provide

any one of the six memory and control function commands.

One control function command instructs the DS18B20 to perform a temper ature measurement. Th e result

of this measurement will be placed in the DS18B20’s scratch-pad memory, and may be read by issuing a

memory function command which reads the contents of the scratchpad memory. The temperature alarm

triggers TH and TL consist of 1 byte EEPROM each. If the alarm search command is not applied to the

DS18B20, these registers may be used as general purpose user memory. The scratchpad also contains a

configuration byte to set the desired resolution of the temp erature to digital conversion. Writing TH, T L,

and the configuration byte is done using a memory function command. Read access to these registers is

through the scratchpad. All data is read and written least significant bit first.

DS18B20

3 of 26

DS18B20 BLOCK DIAGRAM Figure 1

PARASITE POWER

The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power

whenever the DQ or VDD pins are high. DQ will provide sufficient power as long as the specified timing

and voltage requirements are met (see the section titled “1-Wire Bus System”). The advantages of

parasite power are twofold: 1) by parasiting off this pin, no local power source is needed for remote

sensing of temperature, and 2) the ROM may be read in absence of normal power.

In order for the DS18B20 to be able to perform accurate temperature conversions, sufficient power must

be provided over the DQ line when a temp erature conversion is taking pla ce. Since the operating current

of the DS18B20 is up to 1.5 mA, the DQ line will not have sufficient drive due to the 5k pullup resistor.

This problem is particularly acute if several DS18B20s are on the same DQ and attempting to convert

simultaneously.

There are two wa ys to assure that the DS18B20 has sufficient supply current during its active conversion

cycle. The first is to provide a strong pullup on the DQ line whenever temper ature conversions or copies

to the E2 memory are taking place. This may be accomplished by using a MOSFET to pull the DQ line

directly to the power suppl y as shown in Figure 2. The DQ line must be switch ed over to the strong pull-

up within 10 µs maximum after issuing an y protocol that involves copying to the E2 memory or initiates

temperature conversions. When using the parasite power mode, the VDD pin must be tied to ground.

Another method of supplying current to the DS18B20 is through the use of an ex ternal power suppl y tied

to the VDD pin, as shown in Figure 3. The advantage to this is that the strong pullup is not required on the

DQ line, and the bus master need not be tied up holding that line high during temperature conversions.

This allows other data traffic on the 1-Wire bus during the conversion time. In addition, any number of

DS18B20s may be placed on the 1-Wire bus, and if they all use external power, they may all

simultaneously perform temperature conversions by issuing the Skip ROM command and then issuing the

Convert T command. Note that as long as the external power supply is active, the GND pin may not be

floating.

The use of parasite power is not recommended above 100°C, since it may not be able to sustain

communications given the higher leakage currents the DS18B20 exhibits at these temperatures. For

64-BIT ROM

AND

1-WIRE PORT

MEMORY AND

CONTROL LOGIC

SCRATCHPAD

8-BIT CRC

ENERAT

TEMPERATURE SENSOR

HIGH TEMPERATURE

TRIGGER, TH

LOW TEMPERATURE

TRIGGER, TL

CONFIGURATION

POWER

SUPPLY

SENSE

INTERNAL VDD

VDD

DS18B20

4 of 26

applications in which such temperatures are likely, it is strongly recommended that VDD be applied to the

DS18B20.

For situations where the bus master does not know whether the DS18B20s on the bus are parasite

powered or supplied with external VDD, a provision is made in the DS18B20 to signal the power supply

scheme used. The bus master can determine if any DS18B20s are on the bus which require the strong

pullup by sending a Skip ROM protocol, then issuing the read power supply command. After this

command is issued, the master then issues read time slots. The DS18B20 will send back “0” on the 1-

Wire bus if it is parasite powered; it will send back a “1” if it is powered from the VDD pin. If the master

receives a “0,” it knows that it must supply the strong pullup on the DQ line during temperature

conversions. See “Memory Command Functions” section for more detail on this command protocol.

STRONG PULLUP FOR SUPPLYING DS18B20 DURING TEM PERATURE

CONVERSION Figure 2

USING VDD TO SUPPLY TEMPERATURE CONVERSION CURRENT Figure 3

µP

+3V - +5.5V

+3V - +5.5V DS18B20

GND VDD

I/O

4.7K

µP

DS18B20

VDD

I/O

+3V - +5.5V

4.7K EXTERNAL

+3V - +5.5V

SUPPLY

TO OTHER

1-WIRE

DEVICES

DS18B20

5 of 26

OPERATION - MEASURING TEMPERATURE

The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the

DS18B20 is configurable (9, 10, 11, or 12 bits), with 12-bit readings the factory default state. This

equates to a temperature resolution of 0.5°C, 0.25°C, 0.125°C, or 0.0625°C. Following the issuance of

the Convert T [44h] command, a temperature conversion is performed and the thermal data is stored in

the scratchpad memory in a 16-bit, sign-extended two’s complement format. The temperature

information can be retrieved over the 1-Wire™ interface by issuing a Read Scratchpad [BEh] command

once the conversion has been performed. The data is transferred over the 1-Wire™ bus, LSB first. The

MSB of the temperature register contains the “sign” (S) bit, denoting whether the temperature is positive

or negative.

Table 2 describes the exact relationship of output data to measured temperature. The table assumes 12-bit

resolution. If the DS18B20 is configured for a lower resolution, insignificant bits will contain zeros. For

Fahrenheit usage, a lookup table or conversion routine must be used.

Temperature/Data Rela ti onships Table 2

232221202-1 2-2 2-3 2-4 LSB

MSb (unit = °C) LSb

SSSSS2

62524MSB

TEMPERATURE DIGITAL OUTPUT

(Binary) DIGITAL

OUTPUT

(Hex)

+125°C 0000 0111 1101 0000 07D0h

+85°C 0000 0101 0101 0000 0550h*

+25.0625°C 0000 0001 1001 0001 0191h

+10.125°C 0000 0000 1010 0010 00A2h

+0.5°C 0000 0000 0000 1000 0008h

0°C 0000 0000 0000 0000 0000h

-0.5°C 1111 1111 1111 1000 FFF8h

-10.125°C 1111 1111 0101 1110 FF5Eh

-25.0625°C 1111 1110 0110 1111 FF6Fh

-55°C 1111 1100 1001 0000 FC90h

*The power on reset register value is +85°C.

O PE RAT ION - ALARM S IGNALING

After the DS18B20 has performed a temperature conversion, the temperature value is compared to the

trigger values stored in TH and TL. Since these registers are 8-bit only, bits 9-12 are ignored for

comparison. The most significant bit of TH or TL directly corresponds to the sign bit of the 16-bit

temperature register. If the result of a temperature measurement is higher than TH or lower than TL, an

alarm flag inside the device is set. This flag is updated with ever y temperature me asurement. As long as

the alarm flag is set, the DS18B20 will respond to the alarm search command. This allows many

DS18B20s to be connected in parallel doing simultaneous temperature measurements. If somewhere the

temperature exceeds the limits, the alarming device(s) can be identified and read immediately without

having to read non-alarming devices.

DS18B20

6 of 26

64-BIT LASERED ROM

Each DS18B20 contains a unique ROM code that is 64-bits long. The first 8 bits are a 1-Wire family code

(DS18B20 code is 28h). The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first

56 bits. (See Figure 4.) The 64-bit ROM and ROM Function Control section allow the DS18B20 to

operate as a 1-Wire device and follow the 1-Wire protocol detailed in the section “1-Wire Bus S ystem.”

The functions required to control sections of the DS18B20 are not accessible until the ROM function

protocol has been satisfied. This protocol is described in the ROM function protocol flow chart (Figure 5).

The 1-Wire bus master must first provide one of five ROM function commands: 1) Read ROM, 2) Match

ROM, 3) Search ROM, 4) Skip ROM, or 5) Alarm Search. After a ROM function sequence has been

successfull y executed, the funct ions specific to the DS 18B20 are accessible and th e bus master ma y then

provide one of the six memory and control function commands.

CRC GENERATION

The DS18B20 has an 8-bit CRC stored in the most significant byte of the 64-bit ROM. The bus master

can compute a CRC value from the first 56-bits of the 64-bit ROM and compare it to the value stored

within the DS18B20 to determine if the ROM data has been received error-free by the bus master. The

equivalent polynomial function of this CRC is:

CRC = X8 + X5 + X4 + 1

The DS18B20 also generates an 8-bit CRC value using the same polynomial function shown above and

provides this value to the bus master to validate the transfer of data bytes. In each case where a CRC is

used for data transfer validation, the bus master must calculate a CRC value using the polynomial

function given above and compare the calculated value to either the 8-bit CRC value stored in the 64-bit

ROM portion of the DS18B20 (for ROM reads) or the 8-bit CRC value computed within the DS18B20

(which is read as a ninth byte when the scratchpad is read). The comparison of CRC values and decision

to continue with an operation are determined entirely by the bus master. There is no circuitry inside the

DS18B20 that prevents a command sequence from proceeding if the CRC stored in or calculated by the

DS18B20 does not match the value generated by the bus master.

The 1-Wire CRC can be generated using a polynomial generator consisting of a shift register and XOR

gates as shown in Figure 6. Additional information about the Dallas 1-Wire C yclic Redundancy Check is

available in Application Note 27 entitled “Understanding and Using Cyclic Redundancy Checks with

Dallas Semiconductor Touch Memory Products.”

The shift register bits are initialized to 0. Then starting with the least significant bit of the family code, 1

bit at a time is shifted in. After the eighth bit of the family code has been entered, then the serial number

is entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC

value. Shifting in the 8 bits of CRC should return the shift register to all 0s.

64-BIT LASERED ROM Figure 4

8-BIT CRC CODE 48-BIT SERIAL NUMBER 8-BIT FAMILY CODE

(28h)

MSB LSB MSB LSB MSB LSB

DS18B20

7 of 26

ROM FUNCTIONS FLOW CHART Figure 5

DS18B20

8 of 26

1-WIRE CRC CODE Figure 6

MEMORY

The DS18B20’s memory is organized as shown in Figure 8. The memory consists of a scratchpad RAM

and a nonvolatile, electrically erasable (E2) RAM, which stores the high and low temperature triggers TH

and TL, and the configuration register. The scratchpad helps insure data integrity when communicating

over the 1-Wire bus. Data is first written to the scratchpad using the Write Scratchpad [4Eh] command.

It can then be verified by using the Read Scratchpad [BEh] command. After the data has been verified, a

Copy Scratchpad [48h] command will transfer the data to the nonvolatile (E2) RAM. This process insures

data integrity when modifying memory.

The scratchpad is organized as eight bytes of memory. The first two bytes contain the LSB and the MSB

of the measured temperature information, respectively. The third and fourth bytes are volatile copies of

TH and TL and are refreshed with every power-on reset. The fifth byte is a volatile copy of the

configuration register and is refreshed with every power-on reset. The configuration register will be

explained in more detail later in this section of the datasheet. The sixth, seventh, and eighth bytes are

used for internal computations, and thus will not read out any predictable pattern.

It is imperative that one writes TH, TL, and config in succession; i.e. a write is not valid if one writes

only to TH and TL, for example, and then issues a reset. If any of these bytes must be written, all three

must be written before a reset is issued.

There is a ninth byte which may be read with a Read Scratchpad [BEh] command. This byte contains a

cyclic redundancy check (CRC) byte which is the CRC over all of the eight previous bytes. This CRC is

implemented in the fashion described in the section titled “CRC Generation”.

Configurati on Register

The fifth byte of the scratchpad memory is the configuration register.

It contains information which will be used by the device to determine the resolution of the temperature to

digital conversion. The bits are organized as shown in Figure 7.

DS18B20 CONFIGURATION REGISTER Figure 7

0R1R0111 1 1

MSb LSb

Bits 0-4 are don’t cares on a write but will always read out “1”.

Bit 7 is a don’t care on a write but will always read out “0”.

(

MSB

)

XOR

(

LSB

)

INPUT

DS18B20

9 of 26

R0, R1: Thermometer resolution bits. Table 3 below defines the resolution of the digital thermometer,

based on the settings of these two bits. There is a direct tradeoff between resolution and conversion time,

as depicted in the AC Electrical Characteristics. The factory default of these EEPROM bits is R0=1 and

R1=1 (12-bit conversions).

Thermometer Resolution Configur ation Table 3

R1 R0 Thermometer

Resolution Max Conversion

Time

0 0 9-bit 93.75ms (tconv/8)

0 1 10-bit 187.5ms (tconv/4)

1 0 11-bit 375ms (tconv/2)

1 1 12-bit 750ms (tconv)

DS18B20 MEMORY MAP Figure 8

TEMPERATURE LSB

TEMPERATURE MSB

TH/USER BYTE 1

TL/USER BYTE 2

CONFIG

RESERVED

CRC

TH/USER BYTE 1

TL/USER BYTE 2

RESERVED

SCRATCHPAD BYTE

E2RAM

CONFIG

DS18B20

10 of 26

1-WIRE BUS SYSTEM

The 1-Wire bus is a system which has a single bus master and one or more slaves. The DS18B20 beh aves

as a slave. The discussion of this bus system is broken down into three topics: hardware configuration,

transaction sequence, and 1-Wire signaling (signal types and timing).

HARDWARE CONFIGUR ATION

The 1-Wire bus has only a single line b y definition; it is important that each device on t he bus be able to

drive it at the appropriate time. To facilitate this, each devi ce attached to the 1-Wire bus must have open

drain or 3-state outputs. The 1-Wire port of the DS18B20 (DQ pin) is open drain with an internal circuit

equivalent to that shown in Figure 9. A multidrop bus consists of a 1-Wire bus with multiple slaves

attached. The 1-Wire bus requires a pullup resistor of approximately 5kΩ.

HARDWARE CONFIGURATION Figure 9

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 this does not

occur and the bus is left low for more than 480 µs, all components on the bus will be reset.

TRANSACTION SEQUENCE

The protocol for accessing the DS18B20 via the 1-Wire port is as follows:

 Initialization

 ROM Function Command

 Memory Function Command

 Transaction/Data

+3V - +5V

4.7K

BUS MASTER

DS18B20 1-WIRE PORT

5 µA

100 OHM

FET

RX = RECEIVE

= TRANSMIT

DS18B20

11 of 26

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 l ets the bus master know that the DS18B20 is on the bus and is ready to operate. For

more details, see the “1-Wire Signaling” section.

ROM FUNCTION COMMANDS

Once the bus master has detected a presence, it can issue one of the five ROM function commands. All

ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in

Figure 5):

Read ROM [33h]

This command allows the bus master to read the DS18B20’s 8-bit family code, unique 48-bit serial

number, and 8-bit CRC. This command can only be used if there is a single DS18B20 on the bus. If more

than one slave is present on the bus, a data collision will occur when all slaves tr y to transmit at the same

time (open drain will produce a wired AND result).

Match ROM [55h]

The match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a

specific DS18 B20 on a multidrop bus. Only th e DS18B20 that exactly matches the 64-bit ROM sequence

will respond to the following memory function command. All slaves that do not match the 64-bit ROM

sequence will wait for a reset pulse. This command can be used with a single or multiple devices on the

bus.

Skip ROM [CCh]

This command can save time in a single drop bus system by allowing the bus master to access the

memory functions without providing the 64-bit ROM code. If more than one slave is present on the bus

and a Read command is issued following the Skip ROM command, data collision will occur on the bus as

multiple slaves transmit simultaneously (open drain pulldowns will produce a wired AND result).

Search ROM [F0h]

When a system is initially brought up, the bus master might not know the number of devices on the 1-

Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process

of elimination to identify the 64-bit ROM codes of all slave devices on the bus.

Alarm Search [ECh]

The flowchart of this command is identical to the Search ROM command. However, the DS18B20 will

respond to this command only if an alarm condition has been encountered at the last temperature

measurement. An alarm condition is defined as a temperature higher than TH or lower than TL. The

alarm condition remains set as long as the DS18B20 is powered up, or until another temperature

measurement reveals a non-alarming value. For alarming, the trigger values stored in EEPROM are taken

into account. If an alarm condition exists and the TH or TL settings are changed, another temperature

conversion should be done to validate any alarm conditions.

DS18B20

12 of 26

Example of a ROM Search

The ROM search process is the repetition of a simple three-step routine: read a bit, read the complement

of the bit, then write the desired value of that bit. The bus master performs this simple, three-step routine

on each bit of the ROM. After one complete pass, the bus m aster knows the contents of the ROM in one

device. The remaining number of devices and their ROM codes may be identified by additional passes.

The following example of the ROM search process assumes four different devices are connected to the

same 1-Wire bus. The ROM data of the four devices is as shown:

ROM1 00110101...

ROM2 10101010...

ROM3 11110101...

ROM4 00010001...

The search process is as follows:

1. The bus master begins the initialization sequence by issuing a reset pulse. The slave devices respond

by issuing simultaneous presence pulses.

2. The bus master will then issue the Search ROM command on the 1-Wire bus.

3. The bus master reads a bit from the 1-Wi re bus. Each device will respond by placing the v alue of the

first bit of their respective ROM data onto the 1-Wire bus. ROM1 and ROM4 will place a 0 onto the

1-Wire bus, i.e., pull it low. ROM2 and ROM3 will place a 1 onto the 1-Wi re bus by allowing the line

to stay high. The result is the logical AND of all devices on the line, therefore the bus m aster se es a 0.

The bus master reads anoth er bit. Since the Search ROM data command is being executed, all of the

devices on the 1-Wire bus respond to this second read by placing the complement of the first bit of

their respective ROM data onto the 1-Wire bus. ROM1 and ROM4 will place a 1 onto the 1-Wire,

allowing the line to stay high. ROM2 and ROM3 will place a 0 onto the 1-Wire, thus it will be pulled

low. The bus master again observes a 0 for the complement of the first ROM data bit. The bus master

has determined that there are some devices on the 1-Wire bus that have a 0 in the first position and

others that have a 1.

The data obtained from the two reads of the three-step routine have the following interpretations:

00 There are still devices attached which have conflicting bits in this position.

01 All devices still coupled have a 0-bit in this bit position.

10 All devices still coupled have a 1-bit in this bit position.

11 There are no devices attached to the 1-Wire bus.

4. The bus master writes a 0. This deselects ROM2 and ROM3 for the remainder of this search pass,

leaving only ROM1 and ROM4 connected to the 1-Wire bus.

5. The bus master performs two more reads and receiv es a 0-bit followed b y a 1-bit. This indicates that

all devices still coupled to the bus have 0s as their second ROM data bit.

6. The bus master then writes a 0 to keep both ROM1 and ROM4 coupled.

7. The bus master executes two reads and receives two 0-bits. This indicates that both 1-bits and 0-bits

exist as the third bit of the ROM data of the attached devices.

DS18B20

13 of 26

8. The bus master writes a 0-bit. This deselects ROM1, leaving ROM4 as the only device still

connected.

9. The bus master reads the remainder of the ROM bits for ROM4 and continues to access the part if

desired. This completes the first pass and uniquely identifies one part on the 1-Wire bus.

10. The bus master starts a new ROM search sequence by repeating steps 1 through 7.

11. The bus master writes a 1-bit. This decouples ROM4, leaving only ROM1 still coupled.

12. The bus master reads the remainder of the ROM bits for ROM1 and communicates to the underlying

logic if desired. This completes the second ROM search pass, in which another of the ROMs was

found.

13. The bus master starts a new ROM search by repeating steps 1 through 3.

14. The bus master writes a 1-bit. This deselects ROM1 and ROM4 for the remainder of this search pass,

leaving only ROM2 and ROM3 coupled to the system.

15. The bus master executes two Read time slots and receives two 0s.

16. The bus master writes a 0-bit. This decouples ROM3 leaving only ROM2.

17. The bus master reads the remainder of the ROM bits for ROM2 and communicates to the underlying

logic if desired. This completes the third ROM search pass, in which another of the ROMs was found.

18. The bus master starts a new ROM search by repeating steps 13 through 15.

19. The bus master writes a 1-bit. This decouples ROM2, leaving only ROM3.

20. The bus master reads the remainder of the ROM bits for ROM3 and communicates to the underlying

logic if desired. This completes the fourth ROM search pass, in which another of the ROMs was

found.

Note the following:

The bus master learns the unique ID number (ROM data pattern) of one 1-Wire device on each ROM

Search operation. The time required to derive the part’s unique ROM code is:

960 µs + (8 + 3 x 64) 61 µs = 13.16 ms

The bus master is therefore capable of identifying 75 different 1-Wire devices per second.

I/O SIGNALING

The DS18B20 requires strict protocols to insure data integrity. The protocol consists of several types of

signaling on one line: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. All of these signals,

with the exception of the presence pulse, are initiated by the bus master.

The initialization sequence required to begin any communication with the DS18B20 is shown in Figure

11. A reset pulse followed by a presence pulse indicates the DS18B20 is ready to send or receive data

given the correct ROM command and memory function command.

DS18B20

14 of 26

The bus master transmits (TX) a reset pulse (a low signal for a minimum of 480 µs). The bus master then

releases the line and goes into a receive mode (RX). The 1-Wire bus is pulled to a high state via the 5K

pullup resistor. After detecting the rising edge on the DQ pin, the DS18B20 waits 15-60 µs and then

transmits the presence pulse (a low signal for 60-240 µs).

MEMO RY COMMAND FUNCTIO NS

The following command protocols are summarized in Table 4, and by the flowchart of Figure 10.

Write Scratchpad [4Eh]

This command writes to the scratchpad of th e DS18B20, starting at the TH register. The next three b ytes

written will be saved in scratchpad memory at address locations 2 through 4. All three bytes must be

written before a reset is issued.

Read Scratchpad [BEh]

This command reads the contents of the scratchpad. Reading will commence at byte 0 and will continue

through the scratchpad until the 9th (byte 8, CRC) byte is read. If not all locations are to be read, the

master may issue a reset to terminate reading at any time.

Copy Scratchpad [48h]

This command copies the scratchpad into the E2 memory of the DS18B20, storing the temper ature trigger

bytes in nonvolatile memory. If the bus master issues read time slots following this command, the

DS18B20 will output 0 on the bus as long as it is busy copying the scratchpad to E2; it will return a 1

when the copy process is complete. If parasite-powered, the bus master has to enable a strong pullup for

at least 10 ms immediately after issuing this command.

Convert T [44h]

This command begi ns a temperature conversion. No further data is required. The temperatur e conversion

will be performed and then the DS18B20 will remain idle. If the bus master issues read time slots

following this command, the DS18B20 will output 0 on the bus as long as it is busy making a temperature

conversion; it will return a 1 when the temperature conversion is complete. If parasite-powered, the bus

master has to enable a strong pullup for a period greater than tconv immediately after issuing this

command.

Recall E2 [B8h]

This command recalls the temperature trigger values and configuration register stored in E2 to the

scratchpad. This recall operation happens automaticall y upon power-up to the DS18B20 as w ell, so valid

data is available in the scratchpad as soon as the d evice h as power applied. W ith ever y read data time slot

issued after this command has been sent, the device will output its temperature converter busy flag:

0=busy, 1=ready.

Read Power Suppl y [B4h]

With every read data time slot issued after this command has been sent to the DS18B20, the device will

signal its power mode: 0=parasite power, 1=external power supply provided.

DS18B20

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MEMORY FUNCTIONS FLOW CHART Figure 10

DS18B20

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MEMORY FUNCTIONS FLOW CHART Figure 10 (cont’d)

DS18B20

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MEMORY FUNCTIONS FLOW CHART Figure 10 (cont’d)

DS18B20

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INITIALI ZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 11

DS18B20 COMMAND SET Table 4

INSTRUCTION DESCRIPTION PROTOCOL

1-WIRE BUS

AFTER ISSUING

PROTOCOL NOTES

TEMPERATURE CONVERSION COMMANDS

Convert T Initiates temperature

conversion. 44h <read temperature busy

status> 1

MEMORY COMMANDS

Read Scratchpad Reads bytes from

scratchpad and reads

CRC byte.

BEh <read data up to 9 bytes>

Write Scratchpad Writes bytes into

scratchpad at addresses 2

through 4 (TH and TL

temperature triggers and

config).

4Eh <write data into 3 bytes

at addr. 2 through. 4> 3

Copy Scratchpad Copies scratchpad into

nonvolatile memory

(addresses 2 through 4

only).

48h <read cop y status> 2

Recall E2Recalls values stored in

nonvolatile memory into

scratchpad (temperature

triggers).

B8h <read temperature busy

status>

Read Power Supply Signals the mode of

DS18B20 power supply

to the master.

B4h <read supply status>

DS18B20

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NOTES:

1. Temperature conversion takes up to 750 ms. After receiving the Convert T protocol, if the part does

not receive power from the VDD pin, the DQ line for the DS18B20 must be held high for at least a

period greater than tconv to provide power during the conversion process. As such, no other activity

may take place on the 1-Wire bus for at least this period after a Convert T command has been issued.

2. After receiving the Copy Scratchpad protocol, if the part does not receive power from the VDD pin, the

DQ line for the DS18B20 must be held high for at least 10 ms to provide power during the copy

process. As such, no other activity may take place on the 1-Wire bus for at least this period after a

Copy Scratchpad command has been issued.

3. All three bytes must be written before a reset is issued.

READ/WRITE TIME SLOTS

DS18B20 data is read and written through the use of time slots to manipulate bits and a command word to

specify the transaction.

Write Time Slots

A write time slot is initiated when the host pulls the data line from a hi gh logi c level to a low logi c level.

There are two types of write time slots: Write 1 time slots and Write 0 time slots. All write time slots

must be a minimum of 60 µs in duration with a minimum of a 1-µs recovery time between individual

write cycles.

The DS18B20 samples the DQ line in a window of 15 µs to 60 µs after the DQ line falls. If the line is

high, a Write 1 occurs. If the line is low, a Write 0 occurs (see Figure 12).

For the host to generate a Write 1 time slot, the data line must be pulled to a logic low level and then

released, allowing the data line to pull up to a high level within 15 µs after the start of the write time slot.

For the host to generate a Write 0 time slot, the data line must be pulled to a logic low level and remain

low for 60 µs.

Read Time Slots

The host generates read time slots when data is to be read f rom the DS18B20. A read time slot is initiated

when the host pulls the data line from a logi c high level to logic low level. The d ata line must remain at a

low logic level for a minimum of 1 µs; output data from the DS18B20 is valid for 15 µs after the falling

edge of the read time slot. The host therefore must stop driving the DQ pin low in ord er to read its state

15 µs from the start of the read slot (see Figure 12). By the end of the read time slot, the DQ pin will pull

back high via the external pullup resistor. All read time slots must be a minimum of 60 µs in duration

with a minimum of a 1-µs recovery time between individual read slots.

Figure 12 shows that the sum of TINIT, TRC, and TSAMPLE must be less than 15 µs. Figure 14 shows that

system timing margin is maximized by keeping TINIT and TRC as small as possible and by locating the

master sample time towards the end of the 15-µs period.

DS18B20

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READ/WRITE TIMI NG DIAGRAM Figure 12

DS18B20

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DETAILED MASTER READ 1 TIMING Figure 13

RECOMME NDED MASTER READ 1 TIMING Figure 14

DS18B20

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Related Ap pli cation Notes

The following Application Notes can be applied to the DS18B20. These notes can be obtained from the

Dallas Semiconductor “Application Note Book,” via ou r website at http://www.dalsemi.com/, or through

our faxback service at (214) 450-0441.

Application Note 27: “Understanding and Using Cyclic Redundancy Checks with Dallas Semiconductor

Touch Memory Product”

Application Note 55: “Extending the Contact Range of Touch Memories”

Application Note 74: “Reading and Writing Touch Memories via Serial Interfaces”

Application Note 104: “Minimalist Temperature Control Demo”

Application Note 106: “Complex MicroLANs”

Application Note 108: “MicroLAN - In the Long Run”

Sample 1-Wire subroutines that can be used in conjunction with AN74 can be downloaded from the

website or our Anonymous FTP Site.

MEMORY FUNCTI O N EXAMPLE Table 5

Example: Bus Master initiates temperature conversion, then reads temperature (parasite power assumed).

MASTER MODE DATA (LSB FIRST) COMMENTS

TX Reset Reset pulse (480-960 µs).

RX Presence Presence pulse.

TX 55h Issue “Match ROM” command.

TX <64-bit ROM code> Issue address for DS18B20.

TX 44h Issue “ Convert T” command.

TX <I/O LINE HIGH> I/O line is held high for at least a period of time greater

than tconv by bus master to allow conversion to complete.

TX Reset Reset pulse.

RX Presence Presence pulse.

TX 55h Issue “Match ROM” command.

TX <64-bit ROM code> Issue address for DS18B20.

TX BEh Issue “Read Scratchpad” command.

RX <9 data bytes> Read entire scratchpad plus CRC; the master now

recalculates the CRC of the eight data bytes received

from the scratchpad, compares the CRC calculated and

the CRC read. If they match, the master continues; if not,

this read operation is repeated.

TX Reset Reset pulse.

RX Presence Presence pulse, done.

DS18B20

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MEMORY FUNCTI O N EXAMPLE Table 6

Example: Bus Master writes memory (parasite power and only one DS18B20 assumed).

MASTER MODE DATA (LSB FIRST) COMMENTS

TX Reset Reset pulse.

RX Presence Presence pulse.

TX CCh Skip ROM command.

TX 4Eh Write Scratchpad command.

TX <3 data bytes> Writes three bytes to scratchpad (TH, TL, and config).

TX Reset Reset pulse.

RX Presence Presence pulse.

TX CCh Skip ROM command.

TX BEh Read Scratchpad command.

RX <9 data bytes> Read entire scratchpad plus CRC. The master now

recalculates the CRC of the eight data bytes received

from the scratchpad, compares the CRC and the two

other bytes read back from the scratchpad. If data match,

the master continues; if not, repeat the sequence.

TX Reset Reset pulse.

RX Presence Presence pulse.

TX CCh Skip ROM command.

TX 48h Copy Scratchpad command; after issuing this command,

the master must wait 10 ms for copy operation to

complete.

TX Reset Reset pulse.

RX Presence Presence pulse, done.

DS18B20

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ABSOLUTE MAXIMUM RATINGS*

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

Operating Temperature -55°C to +125°C

Storage Temperat ure -55°C to +125°C

Soldering Temperature 260°C for 10 seconds

* This is a stress rating only a nd functional operation of the device at these or an y 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.

RECOMMENDED DC OPERATI NG CONDITIONS

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

Supply Voltage VDD Local Power 3.0 5.5 V 1

Data Pin DQ -0.3 +5.5 V 1

Logic 1 VIH 2.2 VCC+0.3 V 1,2

Logic 0 VIL -0.3 +0.8 V 1,3,7

DC ELECTRICAL CHARACTERISTICS (-55°C to +125°C; VDD=3.0V to 5.5V)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

Thermometer Error tERR -10°C to

+85°C ±½ °C

-55°C to

+125°C ±2

Input Logic High VIH Local Power

Parasite Power 2.2

3.0 5.5 V

V1,2

1,2

Input Logic Low VIL -0.3 +0.8 V 1,3,7

Sink Current ILVI/O=0.4V -4.0 mA 1

Standby Current IDDS 750 1000 nA 6,8

Active Current IDD 1 1.5 mA 4

DQ-Input Load Cur rent IDQ 5µA5

AC ELECTRICAL CHARACTERISTICS: NV MEMORY

(-55°C to +125°C; VDD=3.0V to 5.5V)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

NV Write Cycle Time twr 210ms

DS18B20

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AC ELECTRICAL CHARACTERISTICS: (-55°C to +125°C; VDD=3.0 V to 5.5V)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

Temperature

Conversion tCONV 9-bit 93.75 ms

Time 10-bit 187.5

11-bit 375

12-bit 750

Time Slot tSLOT 60 120 µs

Recovery Time tREC 1µs

Write 0 Low Time rLOW0 60 120 µs

Write 1 Low Time tLOW1 115µs

Read Data Valid tRDV 15 µs

Reset Time High tRSTH 480 µs

Reset Time Low tRSTL 480 µs 9

Presence Detect High tPDHIGH 15 60 µs

Presence Detect Low tPDLOW 60 240 µs

Capacitance CIN/OUT 25 pF

NOTES:

1. All voltages are referenced to ground.

2. Logic one voltages are specified at a source current of 1 mA.

3. Logic zero voltages are specified at a sink current of 4 mA.

4. Active current refers to either temperature conversion or writing to the E2 memory. Writing to E2

memory consumes approximately 200 µA for up to 10 ms.

5. Input load is to ground.

6. Standby current specified up to 70°C. Standby current typically is 3 µA a t 125°C.

7. To always guarantee a presence pulse under low voltage parasite power conditions, VILMAX may have

to be reduced to as much as 0.5V.

8. To minimize IDDS, DQ should be: GND ≤ DQ ≤ GND +0.3V or VDD – 0.3V ≤ DQ ≤ VDD.

9. Under parasite power, the max tRSTL before a power on reset occurs is 960 µS.

DS18B20

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