DS1631AU+T& - Hytronics

1 of 16 032305

FEATURES

§ DS1631 and DS1631A Provide ±0.5°C

Accuracy over a 0°C to +70°C Range

§ DS1731 Provides ±1°C Accuracy over a

-10°C to +85°C Range

§ DS1631A Automatically Begins Taking

Temperature Measurements at Power-Up

§ Operating Temperature Range: -55°C to

+125°C (-67°F to +257°F)

§ Temperature Measurements Require No

External Components

§ Output Resolution is User-Selectable to 9,

10, 11, or 12 Bits

§ Wide Power-Supply Range (+2.7V to +5.5V)

§ Converts Temperature-to-Digital Word in

750ms (max)

§ Multidrop Capability Simplifies Distributed

Temperature-Sensing Applications

§ Thermostatic Settings are User-Definable

and Nonvolatile (NV)

§ Data is Read/Written Through 2-Wire Serial

Interface (SDA and SCL Pins)

§ All Three Devices are Available in 8-Pin

mSOP Packages and the DS1631 is Also

Available in a 150mil SO package—see

Table 1 for Ordering Information

PIN CONFIGURATIONS

DESCRIPTION

The DS1631, DS1631A, and DS1731 digital thermometers provide 9, 10, 11, or 12-bit temperature

readings over a -55°C to +125°C range. The DS1631 and DS1631A thermometer accuracy is ±0.5°C

from 0°C to +70°C with 3.0V £ VDD £ 5.5V, and the DS1731 accuracy is ±1°C from -10°C to +85°C with

3.0V £ VDD £ 5.5V. The thermostat on all three devices provides custom hysteresis with user-defined trip

points (TH and TL). The TH and TL registers and thermometer configuration settings are stored in NV

EEPROM so they can be programmed prior to installation. In addition, the DS1631A automatically

begins taking temperature measurements at power-up, which allows it to function as a stand-alone

thermostat. Communication with the DS1631/DS1631A/DS1731 is achieved through a 2-wire serial

interface, and three address pins allow up to eight devices to be multidropped on the same 2-wire bus.

Pin descriptions for the DS1631/DS1631A/DS1731 are provided in Table 2 and user-accessible registers

are summarized in Table 3. A functional diagram is shown in Figure 1.

DS1631/DS1631A/DS1731

High-Precision Digital

Thermometer and Thermostat

www.maxim-ic.com

SO (150mil and 208mil)

(DS1631Z+, DS1631S+)

VDD

GND

TOUT

SOP

(DS1631U+, DS1631AU+,

DS1731U+)

VDD

GND

TOUT

See Table 2 for Pin Descriptions

APPLICATIONS

§ Network Routers and Switches

§ Cellular Base Stations

§ Portable Products

§ Any Space-Constrained Thermally Sensitive

Product

DS1631/DS1631A/DS1731

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Table 1. ORDERING INFORMATION

ORDERING

NUMBER

PACKAGE

MARKING DESCRIPTION

DS1631U+ D1631 (See Note) DS1631 in Lead-Free 8-Pin mSOP

DS1631U+T&R D1631 (See Note) DS1631 in Lead-Free 8-Pin mSOP, 3000 Piece Tape-and-

Reel

DS1631Z+ DS1631Z (See Note) DS1631 in Lead-Free 150 mil 8-Pin SO

DS1631Z+T&R DS1631Z (See Note) DS1631 in Lead-Free 150 mil 8-Pin SO, 2500 Piece Tape-

and-Reel

DS1631AU+ 1631A (See Note) DS1631A in Lead-Free 8-Pin mSOP

DS1631AU+T&R 1631A (See Note) DS1631A in Lead-Free 8-Pin mSOP, 3000 Piece Tape-and-

Reel

DS1631S+ DS1631S (See Note) DS1631 in Lead-Free 208 mil 8-Pin SO

DS1631S+T&R DS1631S (See Note) DS1631 in Lead-Free 208 mil 8-Pin SO, 2000 Piece Tape-

and-Reel

DS1631+ DS1631 (See Note) DS1631 in Lead-Free 300 mil 8-Pin DIP

DS1731U+ D1731 (See Note) DS1731 in Lead-Free 8-Pin mSOP

DS1731U+T&R D1731 (See Note) DS1731 in Lead-Free 8-Pin mSOP, 3000 Piece Tape-and-

Reel

DS1631U D1631 DS1631 in 8-Pin mSOP

DS1631U/T&R D1631 DS1631 in 8-Pin mSOP, 3000-Piece Tape-and-Reel

DS1631Z DS1631Z DS1631 in 150mil 8-Pin SO

DS1631Z/T&R DS1631Z DS1631 in 150mil 8-Pin SO, 2500-Piece Tape-and-Reel

DS1631AU 1631A DS1631A in 8-Pin mSOP

DS1631AU/T&R 1631A DS1631A in 8-Pin mSOP, 3000-Piece Tape-and-Reel

DS1631S DS1631S DS1631 in 208 mil 8-Pin SO

DS1631S/T&R DS1631S DS1631 in Lead-Free 208 mil 8-Pin SO, 2000 Piece Tape-

and-Reel

DS1631 DS1631 DS1631 in 300 mil 8-Pin DIP

DS1731U D1731 DS1731 in 8-Pin mSOP

DS1731U/T&R D1731 DS1731 in 8-Pin mSOP, 3000-Piece Tape-and-Reel

Note: A "+" symbol will also be marked on the package near the Pin 1 indicator

Table 2. DETAILED PIN DESCRIPTION

PIN SYMBOL DESCRIPTION

1 SDA Data Input/Output Pin for 2-Wire Serial Communication Port. Open-Drain.

2 SCL Clock Input Pin for 2-Wire Serial Communication Port.

3 TOUT Thermostat Output Pin. Push-Pull.

4 GND Ground Pin

DS1631/DS1631A/DS1731

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5 A2 Address Input Pin

6 A1 Address Input Pin

7 A0 Address Input Pin

8 VDD Supply Voltage Pin. +2.7V to +5.5V Power-Supply Pin.

DS1631/DS1631A/DS1731

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Figure 1. FUNCTIONAL DIAGRAM

ABSOLUTE MAXIMUM RATINGS*

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

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

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

Solder Dip Temperature (10s) See IPC/JEDEC J-STD-020A Specification

Reflow Oven Temperature +220°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.

CONFIGURATION REGISTER

ND CONTROL LOGIC

ADDRESS

AND

I/O CONTROL

SCL

DIGITAL

COMPARATOR/LOGIC

TH REGISTER

TL REGISTER

OUT

TEMPERATURE SENSOR

and DS ADC

TEMPERATURE REGISTER

VDD

GND

DS1631/DS1631A/DS1731

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DC ELECTRICAL CHARACTERISTICS

(VDD = 2.7V to 5.5V; TA = -55°C to +125°C.)

PARAMETER SYMBOL CONDITION MIN MAX UNITS NOTES

Supply Voltage VDD 2.7 5.5 V 1

0°C to +70°C,

3.0V £ VDD £ 5.5V ±0.5

0°C to +70°C,

2.7V £ VDD < 3.0V ±1

DS1631, DS1631A

Thermometer Error TERR

-55°C to +125°C ±2

°C 2

-10°C to +85°C,

3.0V £ VDD £ 5.5V ±1

-10°C to +85°C,

2.7V £ VDD < 3.0V ±1.5

DS1731

Thermometer Error TERR

-55°C to +125°C ±2

°C 2

Low-Level Input

Voltage VIL -0.5 0.3 x VDD V

High-Level Input

Voltage VIH 0.7 x

VDD VDD + 0.3 V

VOL1 3mA sink current 0 0.4 SDA Low-Level

Output Voltage VOL2 6mA sink current 0 0.6 V

Input Current Each

I/O Pin 0.4 < VI/O < 0.9VDD -10 +10 µA

Temperature

conversion

-55°C to +85°C

Temperature

conversion

+85°C to +125°C

1.25

E2 write 400

Active Supply

Current IDD

Communication only 110 µA

Standby Supply

Current ISTBY 0°C to +70°C 800 nA 4

VOH 1mA source current 2.4 V 1 TOUT Output Logic

Voltage VOL 4mA sink current 0.4 V 1

DS1631/DS1631A/DS1731

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AC ELECTRICAL CHARACTERISTICS

(VDD = 2.7V to 5.5V; TA = -55°C to +125°C.)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

9-bit resolution 93.75

10-bit

resolution 187.5

11-bit

resolution 375

Temperature

Conversion Time tTC

12-bit

resolution 750

SCL Frequency fSCL 0 400 kHz

Bus Free Time

Between a STOP and

START Condition

tBUF 1.3 µs 5

START and Repeated

START Hold Time

from Falling SCL

tHD:STA 0.6 µs 5, 6

Low Period of SCL tLOW 1.3 µs 5

High Period of SCL tHIGH 0.6 µs 5

Repeated START

Condition Setup Time

to Rising SCL

tSU:STA 0.6 µs 5

Data-Out Hold Time

from Falling SCL tHD:DAT 0

0.9 µs 5

Data-In Setup Time to

Rising SCL tSU:DAT 100 ns 5

Rise Time of SDA and

SCL tR 20 + 0.1CB 1000 ns 5, 7

Fall Time of SDA and

SCL tF 20 + 0.1CB 300 ns 5, 7

STOP Setup Time to

Rising SCL tSU:STO 0.6 µs 5

Capacitive Load for

Each Bus Line CB 400 pF

I/O Capacitance CI/O 10 pF

Input Capacitance CI 5 pF

Spike Pulse Width that

can be Suppressed by

Input Filter

tSP 0 50 ns

NOTES:

1) All voltages are referenced to GND.

2) See Figure 2 for Typical Operating Curves.

3) Specified with TOUT pin open; A0, A1, A2 = 0V or VDD; and fSCL ³ 2Hz.

4) Specified with temperature conversions stopped; TOUT pin open; SDA = VDD; SCL = VDD; and A0, A1,

A2 = 0V or VDD.

5) See Timing Diagram in Figure 3. All timing is referenced to 0.9 x VDD and 0.1 x VDD.

6) After this period the first clock pulse is generated.

7) For example, if CB = 300pF, then tR[min] = tF[min] = 50ns.

DS1631/DS1631A/DS1731

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EEPROM AC ELECTRICAL CHARACTERISTICS

(VDD = 2.7V to 5.5V; TA = -55°C to +125°C.)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS

EEPROM Write Cycle Time twr 4 10 ms

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

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

Figure 2. TYPICAL OPERATING CURVES

Figure 3. TIMING DIAGRAM

All timing is referenced to 0.9 x VDD and 0.1 x VDD.

-0.8

-0.6

-0.4

-0.2

0.2

0.4

0.6

0.8

0 10 20 30 40 50 60 70

-3

Mean

REFERENCE TEMPERATURE (°C)

ERROR (°C)

DS1631/DS1631A

-0.8

-0.6

-0.4

-0.2

0.2

0.4

0.6

0.8

-10 010 20 30 40 50 60 70 80

-3 s

Mean

REFERENCE TEMPERATURE (°C)

ERROR (°C)

DS1731

DS1631/DS1631A/DS1731

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Table 3. REGISTER SUMMARY

(USER ACCESS)

SIZE

(BYTES)

MEMORY

TYPE

AND POWER-UP STATE

Temperature

(Read Only) 2 SRAM

Measured temperature in two’s complement

format.

Power-up state: -60ºC (1100 0100 0000 0000)

(Read/Write) 2 EEPROM

Upper alarm trip point in two’s complement

format.

Power-up state: user defined.

(Read/Write) 2 EEPROM

Lower alarm trip point in two’s complement

format.

Power-up state: user defined.

Configuration

(Various bits are

Read/Write and Read

Only—See Table 5)

1 SRAM,

EEPROM

Configuration and status information. Unsigned

data.

6 MSbs = SRAM

2 LSbs (POL and 1SHOT bits) = EEPROM

Power-up state: 100011XX (XX = user defined)

OPERATION—MEASURING TEMPERATURE

The DS1631, DS1631A, and DS1731 measure temperature using bandgap-based temperature sensors. A

delta-sigma analog-to-digital converter (ADC) converts the measured temperature to a 9-, 10-, 11-, or 12-

bit (user-selectable) digital value that is calibrated in °C; for °F applications a lookup table or conversion

routine must be used. Throughout this data sheet, the term “conversion” is used to refer to the entire

temperature measurement and ADC sequence.

The DS1631 and DS1731 always power-up in a low-power idle state, and the Start Convert T command

must be used to initiate conversions. The DS1631A always begins conversions automatically at power-

up.

The DS1631, DS1631A, and DS1731 can be programmed to perform continuous consecutive conversions

(continuous-conversion mode) or to perform single conversions on command (one-shot mode). The

conversion mode is programmed through the 1SHOT bit in the configuration register as explained in the

CONFIGURATION REGISTER section of this data sheet. In continuous-conversion mode, the DS1631A

begins performing continuous conversions immediately at power-up, and the DS1631 and DS1731 begin

continuous conversions after a Start Convert T command is issued. For all three devices, consecutive

conversions continue to be performed until a Stop Convert T command is issued, at which time the device

goes into a low-power idle state. Continuous conversions can be restarted at any time using the Start

Convert T command.

In one-shot mode the DS1631A performs a single conversion at power-up, and the DS1631 and DS1731

perform a single temperature conversion when a Start Convert T command is issued. For all three

devices, when the conversion is complete the device enters a low-power idle state and remains in that

state until a single temperature conversion is again initiated by a Start Convert T command.

The resolution of the output digital temperature data is user-configurable to 9, 10, 11, or 12 bits,

corresponding to temperature increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively. The

default resolution at power-up is 12 bits, and it can be changed through the R0 and R1 bits in the

configuration register. Note that the conversion time doubles for each additional bit of resolution.

After each conversion, the digital temperature is stored as a 16-bit two’s complement number in the two-

byte temperature register as shown in Figure 4. The sign bit (S) indicates if the temperature is positive or

negative: for positive numbers S = 0 and for negative numbers S = 1. The Read Temperature command

DS1631/DS1631A/DS1731

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provides user access to the temperature register. Bits 3 through 0 of the temperature register are

hardwired to 0. When the device is configured for 12-bit resolution, the 12 MSbs (bits 15 through 4) of

the temperature register contain temperature data. For 11-bit resolution, the 11 MSbs (bits 15 through 5)

of the temperature register contain data, and bit 4 is 0. Likewise, for 10-bit resolution, the 10 MSbs (bits

15 through 6) contain data, and for 9-bit the 9 MSbs (bits 15 through 7) contain data, and all unused LSbs

contain 0s. Table 4 gives examples of 12-bit resolution output data and the corresponding temperatures.

Figure 4. TEMPERATURE, TH, AND TL REGISTER FORMAT

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

MS Byte S 26 2

5 2

4 2

3 2

2 2

1 2

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

LS Byte 2-1 2

-2 2

-3 2

-4 0 0 0 0

Table 4. 12-BIT RESOLUTION TEMPERATURE/DATA RELATIONSHIP

TEMPERATURE

(°C)

DIGITAL OUTPUT

(BINARY)

DIGITAL OUTPUT

(HEX)

+125 0111 1101 0000 0000 7D00h

+25.0625 0001 1001 0001 0000 1910h

+10.125 0000 1010 0010 0000 0A20h

+0.5 0000 0000 1000 0000 0080h

0 0000 0000 0000 0000 0000h

-0.5 1111 1111 1000 0000 FF80h

-10.125 1111 0101 1110 0000 F5E0h

-25.0625 1110 0110 1111 0000 E6F0h

-55 1100 1001 0000 0000 C900h

OPERATION—THERMOSTAT FUNCTION

The thermostat output (TOUT) is updated after every temperature conversion, based on a comparison

between the measured digital temperature and user-defined upper and lower thermostat trip points. TOUT

remains at the updated value until the next conversion completes. When the measured temperature meets

or exceeds the value stored in the upper trip-point register (TH), TOUT becomes active and remains active

until the measured temperature falls below the value stored in the lower trip-point register (TL) (see

Figure 5). This allows the user to program any amount of hysteresis into the output response. The active

state of TOUT is user-programmable through the polarity bit (POL) in the configuration register.

The user-defined values in the TH and TL registers (see Figure 4) must be in two’s complement format

with the MSb (bit 15) containing the sign bit (S). The TH and TL resolution is determined by the R0 and

R1 bits in the configuration register (see Table 6), so the TH and TL resolution matches the output

temperature resolution. For example, for 10-bit resolution bits 5 through 0 of the TH and TL registers read

out as 0 (even if 1s are written to these bits), and the converted temperature is compared to the 10 MSbs

of TH and TL.

The TH and TL registers are stored in EEPROM; therefore, they are NV and can be programmed prior to

device installation. Writing to and reading from the TH and TL registers is achieved using the Access TH

DS1631/DS1631A/DS1731

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and Access TL commands. When making changes to the TH and TL registers, conversions should first be

stopped using the Stop Convert T command if the device is in continuous conversion mode. Note that if

the thermostat function is not used, the TH and TL registers can be used as general-purpose NV memory.

Another thermostat feature is the temperature high and low flags (THF and TLF) in the configuration

at anytime since the device was powered up. These bits power up as 0s, and if the temperature ever

exceeds the TH register value, the THF bit is set to 1, or if the temperature ever falls below the TL value,

the TLF bit is set to 1. Once THF and/or TLF has been set, it remains set until overwritten with a 0 by the

user or until the power is cycled.

DS1631A STAND-ALONE THERMOSTAT OPERATION

Since the DS1631A automatically begins taking temperature measurements at power-up, it can function

as a standalone thermostat (i.e., it can provide thermostatic operation without microcontroller

communication). For standalone operation, the NV TH and TL registers and the POL and 1SHOT bits in

the configuration register should be programmed to the desired values prior to installation. Since the

default conversion resolution at power-up is 12 bits (R1 = 1 and R0 = 1 in the configuration register), the

conversion resolution is always 12 bits during standalone thermostat operation.

Figure 5. THERMOSTAT OUTPUT OPERATION

CONFIGURATION REGISTER

The configuration register allows the user to program various DS1631 options such as conversion

resolution, TOUT polarity, and operating mode. It also provides information to the user about conversion

status, EEPROM activity, and thermostat activity. The configuration register is arranged as shown in

Figure 6 and detailed descriptions of each bit are provided in Table 5. This register can be read from and

written to using the Access Config command. When writing to the configuration register, conversions

should first be stopped using the Stop Convert T command if the device is in continuous conversion

mode. Note that the POL and 1SHOT bits are stored in EEPROM so they can be programmed prior to

installation is desired. All other configuration register bits are SRAM and power up in the state shown in

Table 5.

Figure 6. CONFIGURATION REGISTER

MSb

it 6

it 5

it 4

it 3

it 2

it 1 LSb

DONE THF TLF NVB R1 R0 POL* 1SHOT*

*NV (EEPROM)

TL THTEMP

POL = 1 (TOUT IS ACTIVE HIGH)

LOGIC 0

LOGIC 1 TOUT

DS1631/DS1631A/DS1731

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Table 5. CONFIGURATION REGISTER BIT DESCRIPTIONS

BIT NAME

(USER ACCESS) FUNCTIONAL DESCRIPTION

DONE—Temperature

Conversion Done

(Read Only)

Power-up state = 1.

DONE = 0. Temperature conversion is in progress.

DONE = 1. Temperature conversion is complete.

THF—Temperature High Flag

(Read/Write)

Power-up state = 0.

THF = 0. The measured temperature has not exceeded the value

stored in the TH register since power-up.

THF = 1. At some point since power-up the measured temperature

has been higher than the value stored in the TH register. THF remains

a 1 until it is overwritten with a 0 by the user, the power is cycled, or

a Software POR command is issued.

TLF—Temperature Low Flag

(Read/Write)

Power-up state = 0.

TLF = 0. The measured temperature has not been lower than the

value stored in the TL register since power-up.

TLF = 1. At some point since power-up the measured temperature

has been lower than the value stored in the TL register. TLF remains a

1 until it is overwritten with a 0 by the user, the power is cycled, or a

Software POR command is issued.

NVB—NV Memory Busy

(Read Only)

Power-up state = 0.

NVB = 1. A write to EEPROM memory is in progress.

NVB = 0. NV memory is not busy.

R1—Resolution Bit 1

(Read/Write)

Power-up state = 1.

Sets conversion, TH, and TL resolution (see Table 6).

R0—Resolution Bit 0

(Read/Write)

Power-up state = 1.

Sets conversion, TH, and TL resolution (see Table 6).

POL*—TOUT Polarity

(Read/Write)

Power-up state = last value written to this bit.

POL = 1. TOUT is active high.

POL = 0. TOUT is active low.

1SHOT*—Conversion Mode

(Read/Write)

Power-up state = last value written to this bit.

1SHOT = 1. One-Shot Mode. The Start Convert T command initiates

a single temperature conversion and then the device goes into a low-

power standby state.

1SHOT = 0. Continuous Conversion Mode. The Start Convert T

command initiates continuous temperature conversions.

*Stored in EEPROM

Table 6. RESOLUTION CONFIGURATION

R1 R0

RESOLUTION

(BIT)

CONVERSION TIME

(MAX)

0 0 9 93.75ms

0 1 10 187.5ms

1 0 11 375ms

1 1 12 750ms

DS1631/DS1631A/DS1731

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2-WIRE SERIAL DATA BUS

The DS1631, DS1631A, and DS1731 communicate over a bidirectional 2-wire serial data bus that

consists of a serial clock (SCL) signal and serial data (SDA) signal. The DS1631, DS1631A, and DS1731

interface to the bus through their SCL input pins and open-drain SDA I/O pins.

The following terminology is used to describe 2-wire communication:

Master Device: Microprocessor/microcontroller that controls the slave devices on the bus. The master

device generates the SCL signal and START and STOP conditions.

Slave: All devices on the bus other than the master. The DS1631, DS1631A, and DS1731 always

function as slaves.

Bus Idle or Not Busy: Both SDA and SCL remain high. SDA is held high by a pullup resistor when the

bus is idle, and SCL must either be forced high by the master (if the SCL output is push-pull) or pulled

high by a pullup resistor (if the SCL output is open-drain).

Transmitter: A device (master or slave) that is sending data on the bus.

Receiver: A device (master or slave) that is receiving data from the bus.

START Condition: Signal generated by the master to indicate the beginning of a data transfer on the

bus. The master generates a START condition by pulling SDA from high to low while SCL is high (see

Figure 8). A “repeated” START is sometimes used at the end of a data transfer (instead of a STOP) to

indicate that the master will perform another operation.

STOP Condition: Signal generated by the master to indicate the end of a data transfer on the bus. The

master generates a STOP condition by transitioning SDA from low to high while SCL is high (see Figure

8). After the STOP is issued, the master releases the bus to its idle state.

Acknowledge (ACK): When a device is acting as a receiver, it must generate an acknowledge (ACK) on

the SDA line after receiving every byte of data. The receiving device performs an ACK by pulling the

SDA line low for an entire SCL period (see Figure 8). During the ACK clock cycle, the transmitting

device must release SDA. A variation on the ACK signal is the “not acknowledge” (NACK). When the

master device is acting as a receiver, it uses a NACK instead of an ACK after the last data byte to indicate

that it is finished receiving data. The master indicates a NACK by leaving the SDA line high during the

ACK clock cycle.

Slave Address: Every slave device on the bus has a unique 7-bit address that allows the master to access

that device. The 7-bit bus address is 1 0 0 1 A2 A1 A0, where A2, A1, and A0 are user-selectable through

the corresponding input pins. The three address pins allow up to eight DS1631s, DS1631As, or DS1731s

to be multidropped on the same bus.

Control Byte: The control byte is transmitted by the master and consists of the 7-bit slave address plus a

read/write (R/W¯¯) bit (see Figure 7). If the master is going to read data from the slave device then R/W¯¯ =

1, and if the master is going to write data to the slave device then R/W¯¯ = 0.

Command Byte: The command byte can be any of the command protocols described in the COMMAND

SET section of this data sheet.

Figure 7. CONTROL BYTE

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

1 0 0 1 A2 A

1 A

0 R/W¯¯

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Figure 8. START, STOP, AND ACK SIGNALS

GENERAL 2-WIRE INFORMATION

§ All data is transmitted MSb first over the 2-wire bus.

§ One bit of data is transmitted on the 2-wire bus each SCL period.

§ A pullup resistor is required on the SDA line and, when the bus is idle, both SDA and SCL must remain

in a logic-high state.

§ All bus communication must be initiated with a START condition and terminated with a STOP

condition. During a START or STOP is the only time SDA is allowed to change states while SCL is

high. At all other times, changes on the SDA line can only occur when SCL is low: SDA must remain

stable when SCL is high.

§ After every 8-bit (1-byte) transfer, the receiving device must answer with an ACK (or NACK), which

takes one SCL period. Therefore, nine clocks are required for every one-byte data transfer.

INITIATING 2-WIRE COMMUNICATION

To initiate 2-wire communication, the master generates a START followed by a control byte containing

the DS1631, DS1631A, or DS1731 slave address. The R/W¯¯ bit of the control byte must be a 0 (“write”)

since the master next writes a command byte. The DS1631/DS1631A/DS1731 responds with an ACK

after receiving the control byte. This must be followed by a command byte from the master, which

indicates what type of operation is to be performed. The DS1631/DS1631A/DS1731 again respond with

an ACK after receiving the command byte.

If the command byte is a Start Convert T or Stop Convert T command (see Figure 9a), the transaction is

finished, and the master must issue a STOP to signal the end of the communication sequence. If the

command byte indicates a write or read operation, additional actions must occur as explained in the

following sections.

2-WIRE WRITES

The master can write data to the DS1631/DS1631A/DS1731 by issuing an Access Config, Access TH, or

Access TL command following the control byte (see Figures 9b and 9d). Since the R/W¯¯ bit in the control

byte was a 0 (“write”), the DS1631/DS1631A/DS1731 are already prepared to receive data. Therefore,

after receiving an ACK in response to the command byte, the master device can immediately begin

transmitting data. When writing to the configuration register, the master must send one byte of data, and

when writing to the TH or TL registers the master must send two bytes of data. After receiving each data

byte, the DS1631/DS1631A/DS1731 respond with an ACK, and the transaction is finished with a STOP

from the master.

SCL

SDA

START

Condition

STOP

Condition

…

ACK (or NACK)

From Receiver

DS1631/DS1631A/DS1731

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2-WIRE READS

The master can read data from the DS1631/DS1631A/DS1731 by issuing an Access Config, Access TH,

Access TL, or Read Temperature command following the control byte (see Figures 9c and 9e). After

receiving an ACK in response to the command, the master must generate a repeated START followed by

a control byte with the same slave address as the first control byte. However, this time the R/W¯¯ bit must

be a 1, which tells the DS1631/DS1631A/DS1731 that a “read” is being performed. After the

DS1631/DS1631A/DS1731 send an ACK in response to this control byte, it begins transmitting the

requested data on the next clock cycle. One byte of data will be transmitted when reading from the

configuration register after which the master must respond with a NACK followed by a STOP. For two-

byte reads (i.e., from the Temperature, TH, or TL register), the master must respond to the first data byte

with an ACK and to the second byte with a NACK followed by a STOP. If only the most significant byte

of data is needed, the master can issue a NACK followed by a STOP after reading the first data byte.

COMMAND SET

The DS1631/DS1631A/DS1731 command set is detailed below:

Start Convert T [ 51h ]

Initiates temperature conversions. If the part is in one-shot mode (1SHOT = 1), only one conversion is

performed. In continuous mode (1SHOT = 0), continuous temperature conversions are performed until a

Stop Convert T command is issued.

Stop Convert T [ 22h ]

Stops temperature conversions when the device is in continuous conversion mode (1SHOT = 0).

Read Temperature [ AAh ]

Reads last converted temperature value from the 2-byte temperature register.

Access TH [ A1h ]

Reads or writes the 2-byte TH register.

Access TL [ A2h ]

Reads or writes the 2-byte TL register.

Access Config [ ACh ]

Reads or writes the 1-byte configuration register.

Software POR [ 54h ]

Initiates a software power-on-reset (POR), which stops temperature conversions and resets all registers

and logic to their power-up states. The software POR allows the user to simulate cycling the power

without actually powering down the device.

DS1631/DS1631A/DS1731

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Figure 9 (a, b, c, d, e). 2-WIRE INTERFACE TIMING

THERM = DS1631, DS1631A, or DS1731

a) Issue a "Start Convert T” or “Stop Convert T” Command

S11

00 A2 A1 A0 WAC7C6C5C4 A

C3 C1 C0 P

Control Byte Command Byte

START STOP

ACK

(THERM)

SCL

SDA

ACK

(THERM)

d) Write to the T

or T

A2 A1 A0 C2

SCL

SDA S11

00W

Control Byte

START ACK

(THERM)

C7 C6 C5 C4 C3 C1 C0

Command Byte ACK

(THERM)

D6 D5 D3 D2 D0D7D6 D5 D4 D3 D2 D1 D0

D7 A

D1 P

LS Data Byte

(from Master)

MS Data Byte

(from Master)

STOP

ACK

(THERM)

ACK

(THERM)

e) Read From the Temperature, T

, or T

AD2D1D0D6 D5 D4 D3

A2 A1 A0

AC4 C3 C2 C1C7 C6 C5A2 A1 A0 A

ACK

(THERM)

Repeat

START

SCL

SDA S11

00 W

Control Byte

START

Command Byte

S11 R

Control Byte MS Data Byte

(from THERM)

…

ACK

(THERM)

ACK

(THERM)

ACK

(Master)

D5 N

D6 D4 D3 D2 D1 D0 P

LS Data Byte

(from THERM)

STOP

…

NACK

(Master)

(THERM) (THERM)

AD2D6 D5 D4 D3 D1 D0A0 WAA1 1 0 1 0 1100AD7A2

b) Write to the Configuration Register

S1 100

Control ByteSTART

SCL

SDA

ACK Command Byte

Data Byte

(from Master)

STOP

ACK ACK

(THERM)

NA1S1 1

00 A2 A1 A0 W010 A

1100 D6 D5 D4 D3 D2 D1 D0 P

S1 1

00 A2 A1 A0 RA

c) Read From the Configuration Register

ACK

(THERM)

Repeat

START

SCL

SDA

Control Byte

START Command Byte Data Byte

(from THERM)

STOP

NACK

(Master)

Control Byte

ACK

(THERM)

ACK

(THERM)

DS1631/DS1631A/DS1731

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OPERATION EXAMPLE

In this example, the master configures the DS1631/DS1631A/DS1731 (A1A2A3 = 000) for continuous

conversions and thermostatic function.

MASTER

MODE

THERMETER*

MODE

DATA

(MSb first) COMMENTS

TX RX START START condition from MASTER.

TX RX 90h

MASTER sends control byte with R/W¯¯ = 0.