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)

(Read/Write)

2

EEPROM

Upper alarm trip point in two’s complement

format.

Factory state: 15ºC (0000 1111 0000 0000)

(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