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DS1631AU

P1-P3P4-P6P7-P9P10-P12P13-P15
DS1631/DS1631A/DS1731
7 of 15
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: -60ºC (1100 0100 0000 0000)
T
H
(Read/Write)
2 EEPROM
Upper alarm trip point in two’s complement
format.
Factory state: 15ºC (0000 1111 0000 0000)
T
L
(Read/Write)
2 EEPROM
Lower alarm trip point in two’s complement
format.
Factory state: 10ºC (0000 1010 0000 0000)
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 begins conversions automatically at power-up in the
mode determined by the configuration register’s 1SHOT bit.
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
8 of 15
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
9 of 15
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
b
it 6
b
it 5
b
it 4
b
it 3
b
it 2
b
it 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
P1-P3P4-P6P7-P9P10-P12P13-P15

DS1631AU

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SENSOR DIGITAL -55C-125C 8UMAX
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