DS1621
TEMPERATURE MEASURING CIRCUITRY Figure 2
SLOPE ACCUMULATOR
PRESET
COMPARE
LOW TEMPERATURE
COEFFICIENT OSCILLATOR
SET/CLEAR
LSB
COUNTER
PRESET
INC
=0
TEMPERATURE REGISTER
HIGH TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
STOP
=0
TEMPERATURE/DATA RELATIONSHIPS Table 2
TEMPERATURE
DIGITAL OUTPUT
(Binary)
DIGITAL OUTPUT
(Hex)
+125°C
+25°C
+½°C
+0°C
-½°C
-25°C
-55°C
01111101 00000000
00011001 00000000
00000001 00000000
00000000 00000000
11111111 10000000
11100111 00000000
11001001 00000000
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
1
0
0
1
1
0
0
1
1
0
0
0
0
0
0
T = -25°C
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DALLAS [ DALLAS SEMICONDUCTOR ]
