Datasheet DS75LXU+T-R, DS75LX Datasheet (Maxim Integrated Producs)

1 of 13 050307

GENERAL DESCRIPTION

This low-voltage (1.7V to 3.7V) digital thermometer
and thermostat provides 9, 10, 11, or 12-bit digital
temperature readings over a -55°C to +125°C range
with ±2°C accuracy over a -25°C to +100°C range. At
power-up, the DS75LX defaults to 9-bit resolution for
software compatibility with the LM75. Communication
with the DS75LX is achieved through a simple 2-wire
serial interface. Three tri-state address pins allow up
to 27 DS75LX devices to operate on the same 2-wire
bus, which greatly simplifies distributed temperature­sensing applications.

The DS75LX thermostat has a dedicated open-drain
output (O.S.) and programmable fault tolerance,
which allow the user to define the number of
consecutive error conditions that must occur before
O.S. is activated. There are two thermostatic
operating modes that control thermostat operation
based on user-defined trip-points (T

OS

and T

HYST

).

APPLICATIONS

Any Thermally Sensitive System
Cellular Base Stations
Telecom Switches and Routers
Servers

PIN CONFIGURATIONS

FEATURES

 1.7V to 3.7V Operating Range
 Tri-State Address Pins Allow Up to 27 Unique

Bus Addresses

 Temperature Measurements Require No

External Components

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

(-67°F to +257°F)

 ±2°C Accuracy from -25°C to +100°C
 Thermometer Resolution Is User-

Configurable from 9 (Default) to 12 Bits (0.5°C
to 0.0625°C Resolution)

 9-Bit Conversion Time is 25ms (max)
 Thermostatic Settings are User-Definable
 Data is Read/Written Through 2-Wire Serial

Interface (SDA and SCL Pins)

 Data Lines Filtered Internally for Noise

Immunity (50ns Deglitch)

 Bus Timeout Feature Prevents Lockup

Problems on 2-Wire Interface

 Multidrop Capability Simplifies Distributed

Temperature-Sensing Applications

 Pin/Software Compatible with the LM75
 Available in 8-Pin μSOP (μMAX

®

) and SO

Packages

ORDERING INFORMATION

PART TEMP RANGE

PIN
PACKAGE

DS75LXS+ -55°C to +125°C

8 SO
(150 mils)

DS75LXS+T&R -55°C to +125°C

8 SO
(150 mils),
2500 Piece

DS75LXU+ -55°C to +125°C

8 µSOP
(µMAX)

DS75LXU+T&R -55°C to +125°C

8 µSOP
(µMAX),
3000 Piece

+ Denotes lead-free package.
T&R denotes tape-and-reel.

Note: A “+” symbol will also be marked on the package near the
pin 1 indicator.

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

DS75LX

Digital Thermometer and Thermostat

with Extended Addressing

www.maxim-ic.com

SO (150 mils)

SC

L

VDD
A

0

A

1

A

2

GND

O.S.

SDA

6

7

3

2

DS75

LX

μ

SOP/μMAX

SC

L

V

DD

A

0

A

1

A

2

GND

O.S.

SDA

6

7

3

2

DS75

LX

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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ABSOLUTE MAXIMUM RATINGS

Voltage Range on VDD, Relative to Ground -0.3V to +4.0V
Voltage Range on Any Other Pin, Relative to Ground -0.3V to +6.0V
Operating Temperature Range -55°C to +125°C
Storage Temperature Range -55°C to +125°C
Soldering Temperature See IPC/JEDEC J-STD-020

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.

The Dallas Semiconductor DS75LX is built to the highest quality standards and manufactured for long-term
reliability. All Dallas Semiconductor devices are made using the same quality materials and manufacturing
methods. However, the DS75LX is not exposed to environmental stresses, such as burn-in, that some industrial
applications require. For specific reliability information on this product, contact the factory in Dallas at (972) 371-

4448.

DC ELECTRICAL CHARACTERISTICS

(1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.)

PARAMETER SYMBOL CONDITIONS MIN MAX UNITS

Supply Voltage VDD (Note 1) 1.7 3.7 V

-25°C to +100°C

±2.0

Thermometer Error
(Note 2)

T

ERR

-55°C to +125°C

±3.0

°C

Input Logic-High SDA,
SCL

V

IH

(Note 3) 0.7 x VDD V

DD

+ 0.3 V

Input Logic-Low SDA,
SCL

V

IL

VSS - 0.3 0.3 x VDD V

V

OL1

3mA sink current 0 0.4

SDA Output Logic-Low
Voltage (Note 3)

V

OL2

6mA sink current 0 0.6

V

O.S. Saturation Voltage VOL

4mA sink current
(Notes 2, 3)

0.8 V

Input Current SDA, SCL 0.4 < V

I/O

< 0.9VDD -10 +10 µA

I/O Capacitance C

I/O

10 pF
Address Input Sink
Current

I

LAH

A0, A1, or A2 tied to V

DD

(Notes 4, 5)

0.2 3.5 µA

Address Input Source
Current

I

LAL

A0, A1, or A2 tied to GND
(Notes 4, 5)

0.2 3.5 µA

Address Voltage High VAH (Note 6) V

DD

- .04 V

Address Voltage Low VAL (Note 6) V

SS

+ .04 V

Standby Current I

DD1

(Notes 4, 5) 13 µA

Active temp conversions 1000 Active Current

(Notes 1, 4, 5)

I

DD

Communication only 100

µA

AC ELECTRICAL CHARACTERISTICS

(1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Resolution

9 12 Bits

9-bit conversions 25

10-bit conversions 50

11-bit conversions 100

Temperature Conversion
Time

t

CONVT

12-bit conversions 200

ms

SCL Frequency f

SCL

400 kHz

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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AC ELECTRICAL CHARACTERISTICS (continued)

(1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Bus Free Time Between
a STOP and START
Condition

t

BUF

(Note 7)

1.3

µs

START and Repeated
START Hold Time from
Falling SCL

t

HD:STA

(Notes 7, 8)

600

ns

Low Period of SCL t

LOW

(Note 7) 1.3 µs

High Period of SCL t

HIGH

(Note 7) 0.6 µs
Repeated START
Condition Setup Time to
Rising SCL

t

SU:STA

(Note 7) 600 ns

Data-Out Hold Time from
Falling SCL

t

HD:DAT

(Notes 7, 9) 0 0.9 µs

Data-In Setup Time to
Rising SCL

t

SU:DAT

(Note 7)

100

ns

Rise Time of SDA and
SCL (Receive)

t

R

(Notes 7, 10)

20 +

0.1C

B

300 ns

Fall Time of SDA and
SCL (Receive)

t

F

(Notes 7, 10)

20 +

0.1CB

300 ns

Spike Suppression
Filter Time (Deglitch
Filter)

t

SS

0 50 ns

STOP Setup Time to
Rising SCL

t

SU:STO

(Note 7) 600 ns

Capacitive Load for Each
Bus Line

C

B

400 pF

Input Capacitance CI 5 pF
Serial Interface Reset
Time

t

TIMEOUT

SDA time low
(Notes 11, 12)

75 325 ms

Note 1: VDD must be decoupled with a high-quality 0.1µF bypass capacitor. X5R or X7R ceramic surface-mount capacitors are

recommended.

Note 2:

Internal heating caused by O.S. loading causes the DS75LX to read approximately 0.5°C higher if O.S. is sinking the max
rated current.

Note 3: All voltages are referenced to ground.
Note 4: I

DD

specified with O.S. pin open and A0–A2 pins grounded.

Note 5:

I

DD

and address leakage specified with VDD at 3.0V and SDA, SCL = 3.0V at 0°C to +70°C.

Note 6: Address pins A0, A1, A2 are directly connected to V

DD

, VSS, or floating with less than 50pF capacitive load.

Note 7: See the timing diagram (Figure 1). All timing is referenced to 0.9 x V

DD

and 0.1 x VDD.

Note 8: After this period, the first clock pulse is generated.
Note 9: The DS75LX provides an internal hold time of at least 75ns on the SDA signal to bridge the undefined region of SCL's falling

edge.

Note 10: For example, if C

B

= 300pF, then tR[min] = tF[min] = 50ns.

Note 11: This timeout applies only when the DS75LX is holding SDA low. Other devices can hold SDA low indefinitely and the DS75LX

will not reset.

Note 12: The DS75LX is available with timeout feature disabled upon special order. Contact Factory.

PIN DESCRIPTION

PIN NAME FUNCTION

1 SDA Data Input/Output for 2-Wire Serial Communication Port (Open Drain)
2 SCL Clock Input for 2-Wire Serial Communication Port
3 O.S. Thermostat Output Open Drain
4 GND Ground
5 A2 Address Input
6 A1 Address Input
7 A0 Address Input

8 VDD

Supply Voltage. +1.7V to +3.7V supply pin. V

DD

must have an external bypass

capacitor to GND. 0.1µF X5R or X7R ceramic SMT caps recommended.

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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BLOCK DIAGRAM

Figure 1. Timing Diagram

TOS AND T

HYST

RE

GIS

TER

S

CONFIGURATION

RE

GIS

TER

TEMPERATURE

RE

GIS

TER

OVERSAMPLING

M

ODU

LATOR

PRECISION

REFEREN

C

E

DIGITAL

DE

C

IMATOR

ADDRESS

AND

I/O CONTROL

A

1

A

2

A

0

SCL

SD

A

VDD

GND

THERMOSTAT

CO

MPARATOR

RP

O.S.

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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OPERATION—MEASURING TEMPERATURE

The DS75LX measures temperature using a bandgap temperature-sensing architecture. An on-board delta-sigma
analog-to-digital converter (ADC) converts the measured temperature to a digital value that is calibrated in degrees
celsius; for Fahrenheit applications a lookup table or conversion routine must be used. The DS75LX is factory­calibrated and requires no external components to measure temperature.

At power-up the DS75LX immediately begins measuring and converting its own temperature to a digital value. The
resolution of the digital output 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, with 9-bit default resolution at power-up. The
resolution is controlled via the R0 and R1 bits in the configuration register as explained in the Configuration
Register section of this data sheet. Note that the conversion time doubles for each additional bit of resolution.

After each temperature measurement and analog-to-digital conversion, the DS75LX stores the temperature as a
16-bit two’s complement number in the 2-byte temperature register (see Figure 2). The sign bit (S) indicates if the
temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. The most recently
converted digital measurement can be read from the temperature register at any time. Since temperature
conversions are performed in the background, reading the temperature register does not affect the operation in
progress.

Bits 3 through 0 of the temperature register are hardwired to 0. When the DS75LX 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 reads out as 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 will contain 0s. Table 1 gives examples of 12-bit resolution digital
output data and the corresponding temperatures.

Figure 2. 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 2

6

2

5

2

4

2

3

2

2

2

1

2

0

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 1. 12-Bit Resolution Temperature/Data Relationship

TEMPERATURE (°C)

DIGITAL OUTPUT

(BINARY)

DIGITAL OUTPUT

(HEX)

[phone] 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

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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Shutdown Mode

For power-sensitive applications, the DS75LX offers a low-power shutdown mode. The SD bit in the configuration
register controls shutdown mode. When SD is changed to 1, the conversion in progress is completed and the result
is stored in the temperature register after which the DS75LX goes into a low-power standby state. The O.S. output
is cleared if the thermostat is operating in interrupt mode, and O.S remains unchanged in comparator mode. The 2­wire interface remains operational in shutdown mode, and writing a 0 to the SD bit returns the DS75LX to normal
operation.

OPERATION—THERMOSTAT

The DS75LX thermostat has two operating modes, comparator mode and interrupt mode, which activate and
deactivate the open-drain thermostat output (O.S.) based on user-programmable trip-points (T

OS

and T

HYST

). The
DS75LX powers up with the thermostat in comparator mode with active-low O.S. polarity and with the
overtemperature trip-point (T

OS

) register set to +80°C and the hysteresis trip-point (T

HYST

) register set to +75°C. If
these power-up settings are compatible with the application, the DS75LX can be used as a stand-alone thermostat
(i.e., no 2-wire communication required). If interrupt mode operation, active-high O.S. polarity, or different T

OS

and

T

HYST

values are desired, they must be programmed after power-up, so stand-alone operatio n is not possible.

In both operating modes, the user can program the thermostat fault tolerance, which sets how many consecutive
temperature readings (1, 2, 4, or 6) must fall outside of the thermostat limits before the thermostat output is
triggered. The fault tolerance is set by the F1 and F0 bits in the configuration register and at power-up the fault
tolerance is 1.

The data format of the T

OS

and T

HYST

registers is identical to that of the temperature register (see Figure 2), i.e., a
2-byte two’s complement representation of the trip-point temperature in degrees celcius with bits 3 through 0
hardwired to 0. After every temperature conversion, the measured temperature is compared to the values in the
T

OS

and T

HYST

registers, and then O.S. is updated based on the result of the comparison and the operating mode.

The number of T

OS

and T

HYST

bits used during the thermostat comparison is equal to the conversion resolution set

by the R1 and R0 bits in the configuration register. For example, if the resolution is 9 bits, only the 9 MSbs of T

OS

and T

HYST

will be used by the thermostat comparator.

The active state of the O.S. output can be changed by the POL bit in the configuration register. The power-up
default is active low.

If the user does not wish to use the thermostat capabilities of the DS75LX, the O.S. output should be left floating.
Note that if the thermostat is not used, the T

OS

and T

HYST

registers can be used for general storage of system data.

Comparator Mode

When the thermostat is in comparator mode, O.S. can be programmed to operate with any amount of hysteresis.
The O.S. output becomes active when the measured temperature exceeds the T

OS

value a consecutive number of
times as defined by the F1 and F0 fault tolerance (FT) bits in the configuration register. O.S. then stays active until
the first time the temperature falls below the value stored in T

HYST

. Putting the device into shutdown mode does not

clear O.S. in comparator mode. Thermostat comparator mode operation with FT = 2 is illustrated in Figure 3.

Interrupt Mode

In interrupt mode, the O.S. output first becomes active when the measured temperature exceeds the TOS value a
consecutive number of times equal to the FT value in the configuration register. Once activated, O.S. can only be
cleared by either putting the DS75LX into shutdown mode or by reading from any register (temperature,
configuration, T

OS

, or T

HYST

) on the device. Once O.S. has been deactivated, it will only be reactivated when the

measured temperature falls below the T

HYST

value a consecutive number of times equal to the FT value. Again, O.S
can only be cleared by putting the device into shutdown mode or reading any register. Thus, this interrupt/clear
process is cyclical between T

OS

and T

HYST

events (i.e, TOS, clear, T

HYST

, clear, TOS, clear, T

HYST

, clear, etc.).

Thermostat interrupt mode operation with FT = 2 is illustrated in Figure 3.

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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Figure 3. O.S. Output Operation Example

Configuration Register

The configuration register allows the user to program various DS75LX options such as conversion resolution,
thermostat fault tolerance, thermostat polarity, thermostat operating mode, and shutdown mode. The configuration
register is arranged as shown in Figure 4 and detailed descriptions of each bit are provided in Table 2. The user
has read/write access to all bits in the configuration register except the MSb, which is a reserved read-only bit. The
entire register is volatile, and thus powers up in its default state.

Figure 4. Configuration Register

MSb bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 LSb

0 R1 R0 F1 F0 POL TM SD

In this example the
DS75LX is configured to
have a fault tolerance of 2.

O.S. Output - Comparator Mode

Conversions

Inactive

Active

Temperature

T

OS

T

HYST

Inactive

Active

O.S. Output - Interrupt Mode

Assumes an interrupt

clear event

has occurred

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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Table 2. Configuration Register Bit Descriptions

BIT NAME DESCRIPTION

0

Reserved

Power-Up State = 0
The master can write to this bit, but it always reads out as a 0.

R1

Conversion Resolution Bit 1

Power-Up State = 0
Sets conversion resolution (see Table 3).

R0

Conversion Resolution Bit 0

Power-Up State = 0
Sets conversion resolution (see Table 3).

F1

Thermostat Fault Tolerance Bit 1

Power-Up State = 0
Sets the thermostat fault tolerance (see Table 4).

F0

Thermostat Fault Tolerance Bit 0

Power-Up State = 0
Sets the thermostat fault tolerance (see Table 4).

POL

Thermostat Output (O.S.) Polarity

Power-Up State = 0
POL = 0 — O.S. is active low.
POL = 1 — O.S. is active high.

TM

Thermostat Operating Mode

Power-Up State = 0
TM = 0 — Comparator mode.
TM = 1 — Interrupt mode.
See the Operation—Thermostat section for a detailed description of
these modes.

SD

Shutdown

Power-Up State = 0
SD = 0 — Active conversion and thermostat operation.
SD = 1 — Shutdown mode.
See the Shutdown Mode section for a detailed description of this mode.

Table 3. Resolution Configuration

R1 R0

THERMOMETER

RESOLUTION (BITS)

MAX CONVERSION

TIME (ms)

0 0 9 25
0 1 10 50
1 0 11 100
1 1 12 200

Table 4. Fault Tolerance Configuration

F1 F0

CONSECUTIVE OUT-OF-LIMITS

CONVERSIONS TO TRIGGER O.S.

0 0 1
0 1 2
1 0 4
1 1 6

REGISTER POINTER

The four DS75LX registers each have a unique two-bit pointer designation, which is defined in Table 5. When
reading from or writing to the DS75LX, the user must “point” the DS75LX to the register that is to be accessed.
When reading from the DS75LX, once the pointer is set it remains pointed at the same register until it is changed.
For example, if the user wants to perform consecutive reads from the temperature register, the pointer only has to
be set to the temperature register one time, after which all reads will automatically be from the temperature register
until the pointer value is changed. On the other hand, when writing to the DS75LX, the pointer value must be
refreshed each time a write is performed, even if the same register is being written to twice in a row.

At power-up, the default pointer value is the temperature register so the temperature register can be read
immediately without resetting the pointer.

Changes to the pointer setting are accomplished as described in the 2-Wire Serial Data Bus.

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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Table 5. Pointer Definition

REGISTER P1 P0

Temperature 0 0
Configuration 0 1
T

HYST

1 0

TOS 1 1

2-WIRE SERIAL DATA BUS

The DS75LX communicates over a standard bidirectional, 2-wire serial data bus that consists of a serial clock
(SCL) signal and serial data (SDA) signal. The DS75LX interfaces to the bus through the SCL input pin and open­drain SDA I/O pin. All communication is MSb first.

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 DS75LX always functions as a slave.
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 5). 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 5). After the
STOP is issued, the master releases the bus to its idle state.

Acknowledge (ACK): When a device (either master or slave) 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 5). 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 DS75LX’s 7-bit bus address depends on the state of the external address pins A0–A2. See Table 6.
The three address pins allow up to 27 DS75LXs to be multidropped on the same bus. When tying an address line
high or low, connect the address line directly to V

DD

or GND. Do not use series resistors on these pins.

Address Byte: The address byte is transmitted by the master and consists of the 7-bit slave address plus a
read/write (R/W¯¯) bit (see Figure 6). 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.

Pointer Byte: The pointer byte is used by the master to tell the DS75LX which register is going to be accessed
during communication. The six MSbs of the pointer byte (see Figure 7) are always 0 and the two LSbs correspond
to the desired register as shown in Table 6.

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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Figure 5. Start, Stop, and ACK Signals

Figure 6. Address Byte

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

a

6

a5 a

4

a

3

a2 a

1

a0 R/W¯¯

The Address Pins A0–A2 are tri-state inputs. These can be low, high, or floating in any combination, resulting in 27
address possibilities. These map into the address byte according to Table 6.

Figure 7. Pointer Byte

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

0 0 0 0 0 0 P1 P0

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 1-byte data transfer.

SCL

SDA

START

Condition

STOP

Condition

ACK (or NACK)

From Receiver

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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Table 6. Address Configuration

A2 A1 A0 ADDRESS

0 0 0 1001000
0 0 1 1001001
0 1 0 1001010
0 1 1 1001011
0 0 FLOAT 0101100
0 FLOAT 0 0101000
0 1 FLOAT 0101101
0 FLOAT 1 0101001
0 FLOAT FLOAT 0110101
1 0 0 1001100
1 0 1 1001101
1 1 0 1001110
1 1 1 1001111
1 0 FLOAT 0101110
1 FLOAT 0 0101010
1 1 FLOAT 0101111
1 FLOAT 1 0101011

1 FLOAT FLOAT 0110110
FLOAT 0 0 1110000
FLOAT 0 1 1110010
FLOAT 1 0 1110011
FLOAT 1 1 1110101
FLOAT 0 FLOAT 1110001
FLOAT FLOAT 0 1110110
FLOAT 1 FLOAT 1110100
FLOAT FLOAT 1 1110111
FLOAT FLOAT FLOAT 0110111

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

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Writing to the DS75LX

To write to the DS75LX, the master must generate a START followed by an address byte containing the DS75LX
bus address. The value of the R/W¯¯ bit must be a 0, which indicates that a write is about to take place. The DS75LX
responds with an ACK after receiving the address byte. This must be followed by a pointer byte from the master,
which tells the DS75LX which register is being written to. The DS75LX again responds with an ACK after receiving
the pointer byte. Following this ACK the master device must immediately begin transmitting data to the DS75LX.
When writing to the configuration register, the master must send one byte of data (see Figure 8a), and when writing
to the T

OS

or T

HYST

registers the master must send two bytes of data (see Figure 8b). After receiving each data

byte, the DS75LX responds with an ACK, and the transaction is finished with a STOP from the master.

Software POR

The soft POR command is hex 54. Issue a write command to the DS75LX. It responds with an ACK. If the next
byte is a 0x54, the DS75LX will reset as if power had been cycled. No ACK is sent by the IC after the POR
command is received.

Reading from the DS75LX

When reading from the DS75LX, if the pointer was already pointed to the desired register during a previous
transaction, the read can be performed immediately without changing the pointer setting. In this case the master
sends a START followed by an address byte containing the DS75LX bus address. The R/W¯¯ bit must be a 1, which
tells the DS75LX that a read is being performed. After the DS75LX sends an ACK in response to the address byte,
the DS75LX begins transmitting the requested data on the next clock cycle. When reading from the configuration
register, the DS75LX transmits one byte of data, after which the master must respond with a NACK followed by a
STOP (see Figure 8c). For 2-byte reads (i.e., from the temperature, T

OS

, or T

HYST

register), the DS75LX transmits
two bytes of data, and the master must respond to the first data byte with an ACK and to the second byte with a
NACK followed by a STOP (see Figure 8d). 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, in which case the transaction will be the same as for
a read from the configuration register.

If the pointer is not already pointing to the desired register, the pointer must first be updated as shown in Figure 8e,
which shows a pointer update followed by a single-byte read. The value of the R/W¯¯ bit in the initial address byte is
a 0 (“write”) since the master is going to write a pointer byte to the DS75LX. After the DS75LX responds to the
address byte with an ACK, the master sends a pointer byte that corresponds to the desired register. The master
must then perform a repeated START followed by a standard 1- or 2-byte read sequence (with R/W¯¯ = 1) as
described in the previous paragraph.

PACKAGE INFORMATION

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package
outline information, go to www.maxim-ic.com/DallasPackInfo

.)

PACKAGE DOCUMENT NO.

8-Pin SO 56-G2008-001C
8-Pin µSOP/µMAX 21-0036J

DS75LX: Digital Thermometer and Thermostat with Extended Addressing

13 of 13

Figure 8. 2-Wire Interface Timing

(DS75LX)

(DS75LX)

A

D2D6

D5 D4

D3

D1

D0

WA

0

00

0

0

00

1AD7

Address ByteSTART

SCL

SDA

ACK

Pointer Byte

P

Data Byte

(from Master)

STOP

ACK

ACK

(DS75LX)

A

D2D6

D5 D4

D3

D1

D0

WA

0

00

0

0

00

1

0

00

0

0

00

1AD7

b) Write to the Configuration Register

S

Address ByteSTART

SCL

SDA

ACK

Pointer Byte

P

Data Byte

(from Master)

STOP

ACK

ACK

c) Write to the T

OS

or T

HYST

Register

SCL

SDA

W

A

Address Byte

START

ACK

(DS75LX)

A

0

0

000

0

P1

P0

Pointer Byte

ACK

(DS75LX)

D4

D6

D5

D3

D2 D0D7D6 D5 D4

D3

D2 D1

D0

D7

A

D1

P

LS Data Byte

(from Master)

A

MS Data Byte

(from Master)

STOP

ACK

(DS75LX)

ACK

(DS75LX)

c) Write to the T

OS

or T

HYST

Register

SCL

SDA

S

W

A

Address Byte

START

ACK

A

0

0

000

0

P1

P0

0

0

000

0

P1

P0

Pointer Byte

ACK

D4

D6

D5

D3

D2 D0D7D6 D5 D4

D3

D2 D1

D0

D7

A

D1

P

LS Data Byte

(from Master)

A

MS Data Byte

(from Master)

STOP

ACK ACK

d) Read Single Byte (new pointer location)

(DS75LX)

START

(from DS75LX)

(Master)

(DS75LX )

(DS75LX)

N

A

0

W

0

00

0

0

D6 D5

D4

D3

D2 D1 D0 P

D7

RA

ACK

Repeat

SCL

SDA

Address Byte

START

Pointer Byte

Data Byte

STOP

NACKAddress Byte

ACK

ACK

P1 P0

N

A

0

S

W

0

00

A

0

0

D6 D5

D4

D3

D2 D1 D0 P

D7

S

RA

ACK

Repeat

SCL

SDA

Address Byte

START

Pointer Byte

Data Byte

STOP

NACKAddress Byte

ACK

ACK

P1 P0P1 P0

on)

SCL

SDA

START

N

D6

D5

D4

D3

D2 D1 D0 P

D7

R

Data Byte

(from DS75LX)

STOP

NACK

(Master)

Address Byte ACK

(DS75LX)

S

e) Read From the Configuration Register (current pointer location)

SCL

SDA

START

N

D6

D5

D4

D3

D2 D1 D0 P

D7

R

Data Byte

STOP

NACK

(Master)

Address Byte ACK

N

D6

D5

D4

D3

D2 D1 D0 P

D7

RA

Data Byte

STOP

NACK

(Master)

Address Byte ACK

a) Read 2-Bytes From the Temperature, T

OS

or T

HYST

Register (current pointer location)

SCL

SDA

START

A

D6 D5

D4

D3 D2 D1 D0D7

1

1

0RA

MS Data Byte

(from DS75LX)

ACK

(Master)

Address Byte ACK

(DS75LX)

N

D6

D5

D4

D3

D2 D1

D0

P

D7

LS Data Byte

(from DS75LX)

STOP

NACK

(Master)

S

Bytes From the Temperature, T

OS

or T

HYST

Register (current pointer location)

SCL

SDA

START

A

D6 D5

D4

D3 D2 D1 D0D7

1

1

0

0

RA

MS Data Byte

ACK

(Master)

Address Byte ACK

N

D6

D5

D4

D3

D2 D1

D0

P

D7

LS Data Byte

STOP

NACK

(Master)

1

1

0

1

1

0

0

1

1

0

1

1

0

0

1

1

0

1

1

0

0

1

1

0

1

1

0

0

1

1

0

1

1

0

0

An address byte value of 1110010 corresponds to A0 connected to V

DD

, A1 connected to GND, and A2 floating.