DS1631 Datasheet, PDF (7/15 Pages) National Semiconductor (TI) – CMOS Dual Peripheral Drivers

Table 3. REGISTER SUMMARY
REGISTER NAME SIZE MEMORY
(USER ACCESS) (BYTES) TYPE
Temperature
(Read Only)
2
SRAM
T_H
(Read/Write)
2
EEPROM
T_L
(Read/Write)
2
EEPROM
Configuration
(Various bits are
Read/Write and Read
Only—See Table 5)
1
SRAM,
EEPROM
DS1631/DS1631A/DS1731
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.
Factory state: 15ºC (0000 1111 0000 0000)
Lower alarm trip point in two’s complement
format.
Factory state: 10ºC (0000 1010 0000 0000)
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
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