Dallas DS1631A High-precision digital thermometer and thermostat Datasheet

DS1631/DS1631A/DS1731
High-Precision Digital
Thermometer and Thermostat
www.maxim-ic.com
FEATURES
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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
8
VDD
2
7
A0
3
6
A1
4
5
A2
SDA
1
SCL
TOUT
GND
mSOP
(DS1631U, DS1631AU, DS1731U)
SDA
1
8
VDD
SCL
2
7
A0
TOUT
3
6
A1
GND
4
5
A2
SO (150mil)
(DS1631Z)
See Table 2 for Pin Descriptions
APPLICATIONS
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Network Routers and Switches
Cellular Base Stations
Portable Products
Any Space-Constrained Thermally Sensitive
Product
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.
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DS1631/DS1631A/DS1731
Table 1. ORDERING INFORMATION
ORDERING
NUMBER
DS1631U
DS1631U/T&R
DS1631Z
DS1631Z/T&R
DS1631AU
DS1631AU/T&R
DS1731U
DS1731U/T&R
PACKAGE
MARKING
D1631
D1631
DS1631Z
DS1631Z
1631A
1631A
D1731
D1731
DESCRIPTION
DS1631 in 8-Pin mSOP
DS1631 in 8-Pin mSOP, 3000-Piece Tape-and-Reel
DS1631 in 150mil 8-Pin SO
DS1631 in 150mil 8-Pin SO, 2500-Piece Tape-and-Reel
DS1631A in 8-Pin mSOP
DS1631A in 8-Pin mSOP, 3000-Piece Tape-and-Reel
DS1731 in 8-Pin mSOP
DS1731 in 8-Pin mSOP, 3000-Piece Tape-and-Reel
Table 2. DETAILED PIN DESCRIPTION
PIN
1
2
3
4
5
6
7
8
SYMBOL
SDA
SCL
TOUT
GND
A2
A1
A0
VDD
DESCRIPTION
Data Input/Output Pin for 2-Wire Serial Communication Port. Open-Drain.
Clock Input Pin for 2-Wire Serial Communication Port.
Thermostat Output Pin. Push-Pull.
Ground Pin
Address Input Pin
Address Input Pin
Address Input Pin
Supply Voltage Pin. +2.7V to +5.5V Power-Supply Pin.
Figure 1. FUNCTIONAL DIAGRAM
CONFIGURATION REGISTER
AND CONTROL LOGIC
VDD
SCL
SDA
A0
A1
A2
GND
TEMPERATURE SENSOR
and DS ADC
ADDRESS
AND
I/O CONTROL
TEMPERATURE REGISTER
TH REGISTER
DIGITAL
COMPARATOR/LOGIC
TL REGISTER
2 of 14
TOUT
DS1631/DS1631A/DS1731
ABSOLUTE MAXIMUM RATINGS*
Voltage on any Pin Relative to Ground
Operating Temperature Range
Storage Temperature Range
Solder Dip Temperature (10s)
Reflow Oven Temperature
-0.5V to +6.0V
-55°C to +125°C
-55°C to +125°C
See IPC/JEDEC J-STD-020A Specification
+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.
DC ELECTRICAL CHARACTERISTICS
(VDD = 2.7V to 5.5V; TA = -55°C to +125°C.)
PARAMETER
Supply Voltage
DS1631, DS1631A
Thermometer Error
DS1731
Thermometer Error
Low-Level Input
Voltage
High-Level Input
Voltage
SDA Low-Level
Output Voltage
Input Current Each
I/O Pin
Active Supply
Current
Standby Supply
Current
TOUT Output Logic
Voltage
SYMBOL
VDD
TERR
TERR
CONDITION
0°C to +70°C,
3.0V £ VDD £ 5.5V
0°C to +70°C,
2.7V £ VDD < 3.0V
-55°C to +125°C
-10°C to +85°C,
3.0V £ VDD £ 5.5V
-10°C to +85°C,
2.7V £ VDD < 3.0V
-55°C to +125°C
VIH
3mA sink current
6mA sink current
0.4 < VI/O < 0.9VDD
IDD
±1
0°C to +70°C
VOH
VOL
1mA source current
4mA sink current
3 of 14
UNITS
V
NOTES
1
°C
2
°C
2
±2
±1
±1.5
±2
0.7 x
VDD
0
0
-10
Temperature
conversion
-55°C to +85°C
Temperature
conversion
+85°C to +125°C
E2 write
Communication only
ISTBY
MAX
5.5
±0.5
-0.5
VIL
VOL1
VOL2
MIN
2.7
0.3 x VDD
V
VDD + 0.3
V
0.4
0.6
V
+10
µA
1
mA
3
1.25
400
110
µA
800
nA
4
0.4
V
V
1
1
2.4
DS1631/DS1631A/DS1731
AC ELECTRICAL CHARACTERISTICS
(VDD = 2.7V to 5.5V; TA = -55°C to +125°C.)
PARAMETER
Temperature
Conversion Time
SCL Frequency
Bus Free Time
Between a STOP and
START Condition
START and Repeated
START Hold Time
from Falling SCL
Low Period of SCL
High Period of SCL
Repeated START
Condition Setup Time
to Rising SCL
Data-Out Hold Time
from Falling SCL
Data-In Setup Time to
Rising SCL
Rise Time of SDA and
SCL
Fall Time of SDA and
SCL
STOP Setup Time to
Rising SCL
Capacitive Load for
Each Bus Line
I/O Capacitance
Input Capacitance
Spike Pulse Width that
can be Suppressed by
Input Filter
SYMBOL
tTC
CONDITION
9-bit resolution
10-bit
resolution
11-bit
resolution
12-bit
resolution
MIN
TYP MAX
93.75
UNITS
NOTES
187.5
375
ms
750
fSCL
0
400
tBUF
1.3
µs
5
tHD:STA
0.6
µs
5, 6
tLOW
tHIGH
1.3
0.6
µs
µs
5
5
tSU:STA
0.6
µs
5
µs
5
ns
5
0
tHD:DAT
0.9
kHz
tSU:DAT
100
tR
20 + 0.1CB
1000
ns
5, 7
tF
20 + 0.1CB
300
ns
5, 7
tSU:STO
0.6
µs
5
CB
400
CI/O
CI
10
5
tSP
0
pF
pF
pF
50
ns
NOTES:
1)
2)
3)
4)
All voltages are referenced to GND.
See Figure 2 for Typical Operating Curves.
Specified with TOUT pin open; A0, A1, A2 = 0V or VDD; and fSCL ³ 2Hz.
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.
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DS1631/DS1631A/DS1731
EEPROM AC ELECTRICAL CHARACTERISTICS
(VDD = 2.7V to 5.5V; TA = -55°C to +125°C.)
PARAMETER
EEPROM Write Cycle Time
EEPROM Writes
EEPROM Data Retention
SYMBOL
twr
NEEWR
tEEDR
CONDITION
MIN
-55°C to +55°C
-55°C to +55°C
50k
10
TYP
4
MAX
10
UNITS
ms
Writes
Years
Figure 2. TYPICAL OPERATING CURVES
DS1731
0.8
0.8
0.6
0.6
0.4
0.4
0.2
ERROR (°C)
ERROR (°C)
DS1631/DS1631A
+3s
0
Mean
-0.2
-3s
-0.4
+3 s
0.2
0
Mean
-0.2
-0.4
-0.6
-3 s
-0.6
-0.8
-0.8
0
10
20
30
40
50
60
70
REFERENCE TEMPERATURE (°C)
-10
0
10
20
30
40
50
60
70
REFERENCE TEMPERATURE (°C)
Figure 3. TIMING DIAGRAM
All timing is referenced to 0.9 x VDD and 0.1 x VDD.
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DS1631/DS1631A/DS1731
Table 3. REGISTER SUMMARY
REGISTER NAME
(USER ACCESS)
SIZE
(BYTES)
MEMORY
TYPE
Temperature
(Read Only)
2
SRAM
TH
(Read/Write)
2
EEPROM
TL
(Read/Write)
2
EEPROM
Configuration
(Various bits are
Read/Write and Read
Only—See Table 5)
1
SRAM,
EEPROM
REGISTER CONTENTS
AND POWER-UP STATE
Measured temperature in two’s complement
format.
Power-up state: -60ºC (1100 0100 0000 0000)
Upper alarm trip point in two’s complement
format.
Power-up state: user defined.
Lower alarm trip point in two’s complement
format.
Power-up state: user defined.
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 12bit (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 powerup.
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 twobyte 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
6 of 14
DS1631/DS1631A/DS1731
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
MS Byte
LS Byte
bit 14
6
S
2
bit 7
bit 6
-1
2
-2
2
bit 13
5
bit 12
4
bit 11
bit 3
bit 2
bit 1
bit 0
0
0
0
0
bit 5
bit 4
2
2
-4
1
bit 8
20
2
2
bit 9
2
2
-3
bit 10
2
2
3
Table 4. 12-BIT RESOLUTION TEMPERATURE/DATA RELATIONSHIP
TEMPERATURE
(°C)
+125
+25.0625
+10.125
+0.5
0
-0.5
-10.125
-25.0625
-55
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
0111 1101 0000 0000
0001 1001 0001 0000
0000 1010 0010 0000
0000 0000 1000 0000
0000 0000 0000 0000
1111 1111 1000 0000
1111 0101 1110 0000
1110 0110 1111 0000
1100 1001 0000 0000
7D00h
1910h
0A20h
0080h
0000h
FF80h
F5E0h
E6F0h
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
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DS1631/DS1631A/DS1731
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
register. These bits provide a record of whether the temperature has been greater than TH or less than TL
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
POL = 1 (TOUT IS ACTIVE HIGH)
TOUT
LOGIC 1
LOGIC 0
TL
TEMP
TH
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
bit 6
bit 5
bit 4
bit 3
bit 2
DONE
THF
TLF
NVB
R1
R0
*NV (EEPROM)
8 of 14
bit 1
LSb
POL* 1SHOT*
DS1631/DS1631A/DS1731
Table 5. CONFIGURATION REGISTER BIT DESCRIPTIONS
BIT NAME
(USER ACCESS)
DONE—Temperature
Conversion Done
(Read Only)
FUNCTIONAL DESCRIPTION
Power-up state = 1.
DONE = 0. Temperature conversion is in progress.
DONE = 1. Temperature conversion is complete.
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.
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.
Power-up state = 0.
NVB = 1. A write to EEPROM memory is in progress.
NVB = 0. NV memory is not busy.
Power-up state = 1.
Sets conversion, TH, and TL resolution (see Table 6).
Power-up state = 1.
Sets conversion, TH, and TL resolution (see Table 6).
Power-up state = last value written to this bit.
POL = 1. TOUT is active high.
POL = 0. TOUT is active low.
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 lowpower standby state.
1SHOT = 0. Continuous Conversion Mode. The Start Convert T
command initiates continuous temperature conversions.
THF—Temperature High Flag
(Read/Write)
TLF—Temperature Low Flag
(Read/Write)
NVB—NV Memory Busy
(Read Only)
R1—Resolution Bit 1
(Read/Write)
R0—Resolution Bit 0
(Read/Write)
POL*—TOUT Polarity
(Read/Write)
1SHOT*—Conversion Mode
(Read/Write)
*Stored in EEPROM
Table 6. RESOLUTION CONFIGURATION
R1
R0
0
0
1
1
0
1
0
1
RESOLUTION CONVERSION TIME
(BIT)
(MAX)
9
93.75ms
10
187.5ms
11
375ms
12
750ms
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DS1631/DS1631A/DS1731
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
A1
A0
R/･W･
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DS1631/DS1631A/DS1731
Figure 8. START, STOP, AND ACK SIGNALS
SDA
…
SCL
…
ACK (or NACK) STOP
From Receiver Condition
START
Condition
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.
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DS1631/DS1631A/DS1731
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 twobyte 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.
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S
1
0
1
A2 A1 A0
Control Byte
0
A
S
1
0
1
A
1
ACK
(THERM)
A2 A1 A0 W
Control Byte
0
0
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START
S 1
0
1
SCL
S 1
0
1
A
0
1
S
1
START
SDA
SCL
0
1
A
0
1
1
Command Byte
1
A
0
A
Command Byte
Command Byte
S 1
1
A2 A1 A0
Control Byte
0
ACK Repeat
(THERM) START
S 1
ACK
(THERM)
0
1
A
A
A
…
…
…
ACK
(Master)
A
…
P
NACK STOP
(Master)
N
THERM = DS1631, DS1631A, or DS1731
LS Data Byte
(from THERM)
D7 D6 D5 D4 D3 D2 D1 D0
MS Data Byte
(from THERM)
P
ACK STOP
(THERM)
D7 D6 D5 D4 D3 D2 D1 D0
ACK
(THERM)
R
LS Data Byte
(from Master)
P
NACK STOP
(Master)
D7 D6 D5 D4 D3 D2 D1 D0 A
Data Byte
(from THERM)
D7 D6 D5 D4 D3 D2 D1 D0 N
ACK
(THERM)
R
ACK
(THERM)
A2 A1 A0
Control Byte
0
MS Data Byte
(from Master)
P
ACK STOP
(THERM)
D7 D6 D5 D4 D3 D2 D1 D0
0
Data Byte
(from Master)
D7 D6 D5 D4 D3 D2 D1 D0 A
ACK
(THERM)
0
ACK Repeat
(THERM) START
0
0
C7 C6 C5 C4 C3 C2 C1 C0 A
ACK
(THERM)
A2 A1 A0 W
Control Byte
0
1
P
ACK STOP
(THERM)
C7 C6 C5 C4 C3 C2 C1 C0 A
ACK
(THERM)
A2 A1 A0 W
Control Byte
0
1
0
Command Byte
1
e) Read From the Temperature, TH , or TL Register
START
SDA
A
ACK
(THERM)
A2 A1 A0 W
Control Byte
0
d) Write to the TH or TL Register
SDA
SCL
c) Read From the Configuration Register
START
SDA
SCL
Command Byte
C7 C6 C5 C4 C3 C2 C1 C0 A
ACK
(THERM)
W
b) Write to the Configuration Register
START
SDA
SCL
a) Issue a "Start Convert T” or “Stop Convert T” Command
DS1631/DS1631A/DS1731
Figure 9 (a, b, c, d, e). 2-WIRE INTERFACE TIMING
DS1631/DS1631A/DS1731
OPERATION EXAMPLE
In this example, the master configures the DS1631/DS1631A/DS1731 (A1A2A3 = 000) for continuous
conversions and thermostatic function.
MASTER
MODE
TX
TX
RX
TX
RX
THERMETER*
MODE
RX
RX
TX
RX
TX
DATA
(MSb first)
START
90h
ACK
ACh
ACK
TX
RX
02h
RX
TX
TX
TX
RX
TX
RX
TX
RX
TX
RX
TX
TX
TX
RX
TX
RX
TX
RX
TX
RX
TX
TX
TX
RX
TX
RX
TX
TX
RX
RX
RX
TX
RX
TX
RX
TX
RX
TX
RX
RX
RX
TX
RX
TX
RX
TX
RX
TX
RX
RX
RX
TX
RX
TX
RX
ACK
STOP
START
90h
ACK
A1h
ACK
28h
ACK
00h
ACK
STOP
START
90h
ACK
A2h
ACK
0Ah
ACK
00h
ACK
STOP
START
90h
ACK
51h
ACK
STOP
COMMENTS
START condition from MASTER.
MASTER sends control byte with R/･W･ = 0.
Acknowledge bit from THERMOMETER.
MASTER sends Access Config command.
Acknowledge bit from THERMOMETER.
MASTER writes a data byte to the configuration register to
put the THERMOMETER in continuous conversion mode
and set the TOUT polarity to active high.
Acknowledge bit from THERMOMETER.
STOP condition from MASTER.
START condition from MASTER.
MASTER sends control byte with R/･W･ = 0.
Acknowledge bit from THERMOMETER.
MASTER sends Access TH command.
Acknowledge bit from THERMOMETER.
MASTER sends most significant data byte for TH = +40°C.
Acknowledge bit from THERMOMETER.
MASTER sends least significant data byte for TH = +40°C.
Acknowledge bit from THERMOMETER.
STOP condition from MASTER.
START condition from MASTER.
MASTER sends control byte with R/･W･ = 0.
Acknowledge bit from THERMOMETER.
MASTER sends Access TL command.
Acknowledge bit from THERMOMETER.
MASTER sends most significant data byte for TL = +10°C.
Acknowledge bit from THERMOMETER.
MASTER sends least significant data byte for TL = +10°C.
Acknowledge bit from THERMOMETER.
STOP condition from MASTER.
START condition from MASTER.
MASTER sends control byte with R/･W･ = 0.
Acknowledge bit from THERMOMETER.
MASTER sends Start Convert T command.
Acknowledge bit from THERMOMETER.
STOP condition from MASTER.
*THERMOMETER = DS1631, DS1631A, or DS1731
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