TMP108

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SBOS663 – APRIL 2013

TEMPERATURE REGISTER

The temperature register is configured as a 12-bit, read-only register that stores the output of the most recent

conversion. Two bytes must be read to obtain data, as shown in Table 3 and Table 4. Note that byte 1 is the

most significant byte, followed by byte 2, the least significant byte. The first 12 bits are used to indicate

temperature. There is no requirement to read the least significant byte if that information is not needed (for

example, for resolution lower than 1°C). Table 5 summarizes the temperature data format. One LSB equals

0.0625°C. Negative numbers are represented in binary twos complement format. Following power-up or reset,

the temperature register reads 0°C until the first conversion is complete. The unused bits in the temperature

register always read '0'.

Table 3. Byte 1 of Temperature Register

D7

D6

D5

D4

D3

D2

D1

D0

T11

T10

T9

T8

T7

T6

T5

T4

Table 4. Byte 2 of Temperature Register

D7

D6

D5

D4

D3

D2

D1

D0

T3

T2

T1

T0

0

0

0

0

DIGITAL OUTPUT

TEMPERATURE (°C)

BINARY

HEX

128

0111 1111 1111

7FF

127.9375

0111 1111 1111

7FF

100

0110 0100 0000

640

80

0101 0000 0000

500

75

0100 1011 0000

4B0

50

0011 0010 0000

320

25

0001 1001 0000

190

0.25

0000 0000 0100

004

0

0000 0000 0000

000

–0.25

1111 1111 1100

FFC

–25

1110 0111 0000

E70

–55

1100 1001 0000

C90

(1)

The temperature sensor ADC resolution is 0.0625°C/count.

Table 5 does not supply a full list of all temperatures. Use the following rules to obtain the digital data format for

a given temperature.

To convert positive temperatures to a digital data format:

Divide the temperature by the resolution. Then, convert the result to binary code with a 12-bit, left-justified

format, and MSB = 0 to denote a positive sign.

Example: (+50°C)/(0.0625°C/count) = 800 = 320h = 0011 0010 0000

To convert negative temperatures to a digital data format:

Divide the absolute value of the temperature by the resolution, and convert the result to binary code with a

12-bit, left-justified format. Then, generate the twos complement of the result by complementing the binary

number and adding one. Denote a negative number with MSB = 1.

Example: (|–25°C|)/(0.0625°C/count) = 400 = 190h = 0001 1001 0000

Twos complement format: 1110 0110 1111 + 1 = 1110 0111 0000

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