DS1621

4 of 16

102299

TEMPERATURE MEASURING CIRCUITRY Figure 2

TEMPERATURE/DATA RELATIONSHIPS Table 2

TEMPERATURE

DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT

(Hex)

+125°C

01111101 00000000

7B00h

+25°C

00011001 00000000

1900h

+½°C

00000001 00000000

0080h

+0°C

00000000 00000000

0000h

-½°C

11111111 10000000

FF80h

-25°C

11100111 00000000

E700h

-55°C

11001001 00000000

C900h

Since data is transmitted over the 2–wire bus MSB first, temperature data may be written to/read from the

DS1621 as either a single byte (with temperature resolution of 1

°C) or as two bytes. The second byte

would contain the value of the least significant (0.5

°C) bit of the temperature reading as shown in Table

1. Note that the remaining 7 bits of this byte are set to all "0"s.

Temperature is represented in the DS1621 in terms of a ½

°C LSB, yielding the following 9–bit format:

T = -25

°C

SLOPE ACCUMULATOR

PRESET

COMPARE

LOW TEMPERATURE

COEFFICIENT OSCILLATOR

COUNTER

PRESET

=0

TEMPERATURE REGISTER

HIGH TEMPERATURE

COEFFICIENT OSCILLATOR

COUNTER

=0

INC

STOP

SET/CLEAR

LSB

1

1

1

0

0

1

1

1

0

0

0

0

0

0

0

0

MSB

LSB