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092502
FEATURES
DS1631 and DS1631A Provide 0.5C
Accuracy over a 0C to +70C Range
DS1731 Provides 1C Accuracy over a
-10C to +85C Range
DS1631A Automatically Begins Taking
Temperature Measurements at Power-Up
Operating Temperature Range: -55C to
+125C (-67F to +257F)
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 -55C to +125C range. The DS1631 and DS1631A thermometer accuracy is
0.5C
from 0C to +70C with 3.0V
V
DD
5.5V, and the DS1731 accuracy is 1C from -10C to +85C with
3.0V
V
DD
5.5V. The thermostat on all three devices provides custom hysteresis with user-defined trip
points (T
H
and T
L
). The T
H
and T
L
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)
(DS1631Z)
SCL
V
DD
A
0
A
1
A
2
GND
T
OUT
SDA
6
8
7
5
3
1
2
4
mSOP
(DS1631U, DS1631AU, DS1731U)
SCL
V
DD
A
0
A
1
A
2
GND
T
OUT
SDA
6
8
7
5
3
1
2
4
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
2 of 14
Table 1. ORDERING INFORMATION
ORDERING
NUMBER
PACKAGE
MARKING
DESCRIPTION
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
DS1731U
D1731
DS1731 in 8-Pin
mSOP
DS1731U/T&R
D1731
DS1731 in 8-Pin
mSOP, 3000-Piece Tape-and-Reel
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
T
OUT
Thermostat Output Pin. Push-Pull.
4
GND
Ground Pin
5
A
2
Address Input Pin
6
A
1
Address Input Pin
7
A
0
Address Input Pin
8
V
DD
Supply Voltage Pin. +2.7V to +5.5V Power-Supply Pin.
Figure 1. FUNCTIONAL DIAGRAM
CONFIGURATION REGISTER
AND CONTROL LOGIC
ADDRESS
AND
I/O CONTROL
A
1
A
2
A
0
SCL
SDA
DIGITAL
COMPARATOR/LOGIC
T
H
REGISTER
T
L
REGISTER
T
OUT
TEMPERATURE SENSOR
and
DS ADC
TEMPERATURE REGISTER
V
DD
GND
DS1631/DS1631A/DS1731
3 of 14
ABSOLUTE MAXIMUM RATINGS*
Voltage on any Pin Relative to Ground
-0.5V to +6.0V
Operating Temperature Range
-55C to +125C
Storage Temperature Range
-55C to +125C
Solder Dip Temperature (10s)
See IPC/JEDEC J-STD-020A Specification
Reflow Oven Temperature
+220C
* These are stress ratings only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods of time may affect reliability.
DC ELECTRICAL CHARACTERISTICS
(V
DD
= 2.7V to 5.5V; T
A
= -55C to +125C.)
PARAMETER
SYMBOL
CONDITION
MIN
MAX
UNITS NOTES
Supply Voltage
V
DD
2.7
5.5
V
1
0C to +70C,
3.0V
V
DD
5.5V
0.5
0C to +70C,
2.7V
V
DD
< 3.0V
1
DS1631, DS1631A
Thermometer Error
T
ERR
-55C to +125C
2
C
2
-10C to +85C,
3.0V
V
DD
5.5V
1
-10C to +85C,
2.7V
V
DD
< 3.0V
1.5
DS1731
Thermometer Error
T
ERR
-55C to +125C
2
C
2
Low-Level Input
Voltage
V
IL
-0.5
0.3 x V
DD
V
High-Level Input
Voltage
V
IH
0.7 x
V
DD
V
DD
+ 0.3
V
V
OL1
3mA sink current
0
0.4
SDA Low-Level
Output Voltage
V
OL2
6mA sink current
0
0.6
V
Input Current Each
I/O Pin
0.4 < V
I/O
< 0.9V
DD
-10
+10
A
Temperature
conversion
-55C to +85C
1
Temperature
conversion
+85C to +125C
1.25
mA
E
2
write
400
Active Supply
Current
I
DD
Communication only
110
A
3
Standby Supply
Current
I
STBY
0C to +70C
800
nA
4
V
OH
1mA source current
2.4
V
1
T
OUT
Output Logic
Voltage
V
OL
4mA sink current
0.4
V
1
DS1631/DS1631A/DS1731
4 of 14
AC ELECTRICAL CHARACTERISTICS
(V
DD
= 2.7V to 5.5V; T
A
= -55C to +125C.)
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
t
TC
12-bit
resolution
750
ms
SCL Frequency
f
SCL
0
400
kHz
Bus Free Time
Between a STOP and
START Condition
t
BUF
1.3
s
5
START and Repeated
START Hold Time
from Falling SCL
t
HD:STA
0.6
s
5, 6
Low Period of SCL
t
LOW
1.3
s
5
High Period of SCL
t
HIGH
0.6
s
5
Repeated START
Condition Setup Time
to Rising SCL
t
SU:STA
0.6
s
5
Data-Out Hold Time
from Falling SCL
t
HD:DAT
0
0.9
s
5
Data-In Setup Time to
Rising SCL
t
SU:DAT
100
ns
5
Rise Time of SDA and
SCL
t
R
20 + 0.1C
B
1000
ns
5, 7
Fall Time of SDA and
SCL
t
F
20 + 0.1C
B
300
ns
5, 7
STOP Setup Time to
Rising SCL
t
SU:STO
0.6
s
5
Capacitive Load for
Each Bus Line
C
B
400
pF
I/O Capacitance
C
I/O
10
pF
Input Capacitance
C
I
5
pF
Spike Pulse Width that
can be Suppressed by
Input Filter
t
SP
0
50
ns
NOTES:
1) All voltages are referenced to GND.
2) See Figure 2 for Typical Operating Curves.
3) Specified with T
OUT
pin open; A
0
, A
1
, A
2
= 0V or V
DD
; and f
SCL
2Hz.
4) Specified with temperature conversions stopped; T
OUT
pin open; SDA = V
DD
; SCL = V
DD
; and A
0
, A
1
,
A
2
= 0V or V
DD
.
5) See Timing Diagram in Figure 3. All timing is referenced to 0.9 x V
DD
and 0.1 x V
DD
.
6) After this period the first clock pulse is generated.
7) For example, if C
B
= 300pF, then t
R
[min] = t
F
[min] = 50ns.
DS1631/DS1631A/DS1731
5 of 14
EEPROM AC ELECTRICAL CHARACTERISTICS
(V
DD
= 2.7V to 5.5V; T
A
= -55C to +125C.)
PARAMETER
SYMBOL
CONDITION
MIN
TYP
MAX
UNITS
EEPROM Write Cycle Time
t
wr
4
10
ms
EEPROM Writes
N
EEWR
-55C to +55C
50k
Writes
EEPROM Data Retention
t
EEDR
-55C to +55C
10
Years
Figure 2. TYPICAL OPERATING CURVES
Figure 3. TIMING DIAGRAM
All timing is referenced to 0.9 x V
DD
and 0.1 x V
DD
.
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0
10
20
30
40
50
60
70
+3s
-3s
Mean
REFERENCE TEMPERATURE (
C)
ERROR (
C)
DS1631/DS1631A
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
-10
0
10
20
30
40
50
60
70
80
+3s
-3 s
Mean
REFERENCE TEMPERATURE (
C)
ERROR (
C)
DS1731
DS1631/DS1631A/DS1731
6 of 14
Table 3. REGISTER SUMMARY
REGISTER NAME
(USER ACCESS)
SIZE
(BYTES)
MEMORY
TYPE
REGISTER CONTENTS
AND POWER-UP STATE
Temperature
(Read Only)
2
SRAM
Measured temperature in two's complement
format.
Power-up state: -60C (1100 0100 0000 0000)
T
H
(Read/Write)
2
EEPROM
Upper alarm trip point in two's complement
format.
Power-up state: user defined.
T
L
(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, 0.25C, 0.125C, and 0.0625C, 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
7 of 14
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, T
H
, AND T
L
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 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 (T
OUT
) is updated after every temperature conversion, based on a comparison
between the measured digital temperature and user-defined upper and lower thermostat trip points. T
OUT
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 (T
H
), T
OUT
becomes active and remains active
until the measured temperature falls below the value stored in the lower trip-point register (T
L
) (see
Figure 5). This allows the user to program any amount of hysteresis into the output response. The active
state of T
OUT
is user-programmable through the polarity bit (POL) in the configuration register.
The user-defined values in the T
H
and T
L
registers (see Figure 4) must be in two's complement format
with the MSb (bit 15) containing the sign bit (S). The T
H
and T
L
resolution is determined by the R0 and
R1 bits in the configuration register (see Table 6), so the T
H
and T
L
resolution matches the output
temperature resolution. For example, for 10-bit resolution bits 5 through 0 of the T
H
and T
L
registers read
out as 0 (even if 1s are written to these bits), and the converted temperature is compared to the 10 MSbs
of T
H
and T
L
.
The T
H
and T
L
registers are stored in EEPROM; therefore, they are NV and can be programmed prior to
device installation. Writing to and reading from the T
H
and T
L
registers is achieved using the Access TH
DS1631/DS1631A/DS1731
8 of 14
and Access TL commands. When making changes to the T
H
and T
L
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 T
H
and T
L
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
register. These bits provide a record of whether the temperature has been greater than T
H
or less than T
L
at anytime since the device was powered up. These bits power up as 0s, and if the temperature ever
exceeds the T
H
register value, the THF bit is set to 1, or if the temperature ever falls below the T
L
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 T
H
and T
L
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, T
OUT
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
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LSb
DONE
THF
TLF
NVB
R1
R0
POL* 1SHOT*
*NV (EEPROM)
T
L
T
H
TEMP
POL = 1 (T
OUT
IS ACTIVE HIGH)
LOGIC 0
LOGIC 1
T
OUT
DS1631/DS1631A/DS1731
9 of 14
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 T
H
register since power-up.
THF = 1. At some point since power-up the measured temperature
has been higher than the value stored in the T
H
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 T
L
register since power-up.
TLF = 1. At some point since power-up the measured temperature
has been lower than the value stored in the T
L
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, T
H
, and T
L
resolution (see Table 6).
R0--Resolution Bit 0
(Read/Write)
Power-up state = 1.
Sets conversion, T
H
, and T
L
resolution (see Table 6).
POL*--T
OUT
Polarity
(Read/Write)
Power-up state = last value written to this bit.
POL = 1. T
OUT
is active high.
POL = 0. T
OUT
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
10 of 14
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 A
2
A
1
A
0
, where A
2
, A
1
, and A
0
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
A
2
A
1
A
0
R/
W
DS1631/DS1631A/DS1731
11 of 14
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 T
H
or T
L
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
12 of 14
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, T
H
, or T
L
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 T
H
register.
Access TL [ A2h ]
Reads or writes the 2-byte T
L
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
13 of 14
Figure 9 (a, b, c, d, e). 2-WIRE INTERFACE TIMING
THERM = DS1631, DS1631A, or DS1731
C2
a
)
Is
s
u
e
a
"S
ta
r
t
Con
v
e
r
t
T
"
or
"S
top C
onv
e
r
t T"
C
o
mma
nd
S
11
00
A2
A1
A0
W
AC
7
C
6
C
5
C
4
A
C3
C1
C0
P
Co
nt
rol By
t
e
C
o
mma
n
d
B
y
t
e
ST
AR
T
ST
O
P
ACK
(T
HE
RM
)
SC
L
SDA
AC
K
(T
HE
RM
)
d
)
W
r
i
t
e
to
th
e
T
H
or
T
L
Reg
i
st
er
A2
A1
A
0
C2
SC
L
SD
A
S
1
1
0
0W
A
Con
t
r
o
l
B
y
t
e
ST
AR
T
ACK
(T
HE
RM
)
A
C7
C6
C
5
C
4
C3
C1
C0
Com
m
an
d B
y
t
e
ACK
(T
HE
RM
)
D4
D6
D5
D3
D2
D
0
D7
D
6
D5
D4
D3
D2
D1
D0
D7
A
D1
P
L
S
D
a
ta
By
te
(f
rom Ma
st
er)
A
MS
D
a
ta
B
y
t
e
(fro
m Mas
t
e
r
)
ST
O
P
AC
K
(T
HE
R
M
)
AC
K
(T
HE
RM
)
e)
Read
F
r
o
m
t
h
e T
e
mp
erat
u
r
e
,
T
H
, or T
L
Reg
i
st
er
AD
2
D
1
D
0
D6
D5
D4
D3
D7
A2
A1
A0
00
A
C4
C3
C2
C1
C7
C6
C5
A2
A1
A0
A
AC
K
(T
H
E
RM)
Re
pe
at
STAR
T
A
SC
L
SDA
S
11
00
W
Con
t
ro
l
B
y
t
e
ST
AR
T
C0
C
o
mma
n
d
By
te
S
11
R
Con
t
r
o
l
B
y
t
e
M
S
D
a
ta
By
te
(f
r
o
m T
H
E
R
M)
...
...
ACK
(
T
HE
RM
)
AC
K
(T
HE
R
M
)
AC
K
(Ma
s
t
e
r)
D5
N
D6
D4
D3
D2
D1
D
0
P
L
S
D
a
ta
By
te
(f
r
o
m TH
E
R
M)
ST
O
P
D7
...
...
NA
CK
(Mas
te
r)
(T
HERM
)
(
T
HE
RM
)
A
D2
D6
D5
D
4
D3
D1
D0
A0
W
A
A1
1
0
1
0
1
1
00A
D
7
A2
b) Wr
i
t
e
to
t
h
e
C
onfigur
a
t
ion R
e
gis
t
e
r
S1
1
00
Co
nt
rol B
y
t
e
STAR
T
SC
L
SD
A
AC
K
Com
m
an
d B
y
t
e
P
D
a
ta
By
te
(fro
m
M
a
st
er)
ST
O
P
AC
K
AC
K
(T
HE
RM
)
N
A1
S1
1
00
A2
A1
A
0
W
01
0
A
1
10
0
D6
D5
D4
D3
D2
D1
D
0
P
D7
S1
1
00
A2
A
1
A0
R
A
c
)
Re
a
d
Fr
om the
Co
nfigur
a
t
ion Re
gis
t
e
r
AC
K
(T
HERM
)
Re
pe
at
STAR
T
SC
L
SD
A
Con
t
rol B
y
t
e
STAR
T
C
o
mma
n
d
B
y
t
e
D
a
ta
By
te
(fro
m T
H
E
R
M)
ST
O
P
NACK (Ma
s
t
e
r)
Co
nt
rol B
y
t
e
AC
K
(T
HE
R
M
)
AC
K
(T
HE
RM
)
DS1631/DS1631A/DS1731
14 of 14
OPERATION EXAMPLE
In this example, the master configures the DS1631/DS1631A/DS1731 (A
1
A
2
A
3
= 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.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
ACh
MASTER sends Access Config command.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
02h
MASTER writes a data byte to the configuration register to
put the THERMOMETER in continuous conversion mode
and set the T
OUT
polarity to active high.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
STOP
STOP condition from MASTER.
TX
RX
START
START condition from MASTER.
TX
RX
90h
MASTER sends control byte with R/
W
= 0.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
A1h
MASTER sends Access TH command.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
28h
MASTER sends most significant data byte for T
H
= +40C.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
00h
MASTER sends least significant data byte for T
H
= +40C.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
STOP
STOP condition from MASTER.
TX
RX
START
START condition from MASTER.
TX
RX
90h
MASTER sends control byte with R/
W
= 0.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
A2h
MASTER sends Access TL command.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
0Ah
MASTER sends most significant data byte for T
L
= +10C.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
00h
MASTER sends least significant data byte for T
L
= +10C.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
STOP
STOP condition from MASTER.
TX
RX
START
START condition from MASTER.
TX
RX
90h
MASTER sends control byte with R/
W
= 0.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
51h
MASTER sends Start Convert T command.
RX
TX
ACK
Acknowledge bit from THERMOMETER.
TX
RX
STOP
STOP condition from MASTER.
*THERMOMETER = DS1631, DS1631A, or DS1731
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