DS1620 Datasheet, PDF (3/13 Pages) Dallas Semiconductor – Digital Thermometer and Thermostat

TEMPERATURE MEASURING CIRCUITRY Figure 2
SLOPE ACCUMULATOR
DS1620
PRESET
COMPARE
LOW TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
PRESET
SET/CLEAR
LSB
INC
=0
TEMPERATURE REGISTER
HIGH TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
STOP
=0
This calculation is done inside the DS1620 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 DS1620 can measure temperature over the range of
-55°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 DIGITAL OUTPUT
(Binary)
(Hex)
+125°C
0 11111010
00FA
+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
-55°C
1 10010010
0192h
Since data is transmitted over the 3–wire bus LSB first, temperature data can be written to/read from the
DS1620 as either a 9–bit word (taking RST low after the 9^th (MSB) bit), or as two transfers of 8–bit
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