DS1621 Datasheet, PDF (4/16 Pages) Dallas Semiconductor – Digital Thermometer and Thermostat

TEMPERATURE MEASURING CIRCUITRY Figure 2
SLOPE ACCUMULATOR
DS1621
PRESET
COMPARE
LOW TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
PRESET
SET/CLEAR
LSB
INC
=0
TEMPERATURE REGISTER
HIGH TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
STOP
=0
TEMPERATURE/DATA RELATIONSHIPS Table 2
TEMPERATURE
DIGITAL OUTPUT
(Binary)
+125°C
01111101 00000000
+25°C
00011001 00000000
+½°C
00000001 00000000
+0°C
00000000 00000000
-½°C
11111111 10000000
-25°C
11100111 00000000
-55°C
11001001 00000000
DIGITAL OUTPUT
(Hex)
7B00h
1900h
0080h
0000h
FF80h
E700h
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:
MSB
LSB
1 110 0 11 1
0 000 0 00 0
T = -25°C
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