DS1720

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TEMPERATURE MEASURING CIRCUITRY Figure 2

This calculation is done inside the DS1720 to provide 0.

5°C resolution. The temperature reading is

provided in a 9–bit, two’s complement reading by issuing a READ TEMPERATURE command. Table 1

describes the exact relationship of output data to measured temperature. The data is transmitted serially

through the 3–wire serial interface, LSB first. The DS1720 can measure temperature over the range of

–5

5°C to +125°C in 0.5°C increments. For Fahrenheit usage, a lookup table or conversion factor must be

used.

TEMPERATURE/DATA RELATIONSHIPS Table 1

TEMP

DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT

(Hex)

+85

°C

0 10101010

00AA

+25

°C

0 00110010

0032h

+½

°C

0 00000001

0001h

+0

°C

0 00000000

0000h

-½

°C

1 11111111

01FFh

-25

°C

1 11001110

01CEh

Since data is transmitted over the 3–wire bus LSB first, temperature data can be written to/read from the

words, with the most significant 7 bits being ignored or set to zero, as illustrated in Table 1. After the

MSB, the DS1720 will output 0s.

Note that temperature is represented in the DS1720 in terms of a ½

°C LSB, yielding the following 9–bit

format:

MSB

LSB

X

X

X

X

X

X

X

1

1

1

0

0

1

1

1

0

T = -25

°C