DS1722 Datasheet, PDF (4/13 Pages) Dallas Semiconductor – Digital Thermometer with SPI/3-Wire Interface

DS1722
The resolution of the temperature conversion is configurable (8, 9, 10, 11, or 12 bits), with 9-bit readings
the default state. This equates to a temperature resolution of 1.0°C, 0.5°C, 0.25°C, 0.125°C, or 0.0625°C.
Following each conversion, thermal data is stored in the thermometer register in two’s complement
format; the information can be retrieved over the SPI or 3-wire interface with the address set to the
temperature register, 01h (LSB) and then 02h (MSB). Table 2 describes the exact relationship of output
data to measured temperature. The table assumes the DS1722 is configured for 12-bit resolution; if the
device is configured in a lower resolution mode, those bits will contain 0s. The data is transmitted
serially over the digital interface, MSb first for SPI communication and LSb first for 3-wire
communication. The MSb of the temperature register contains the “sign” (S) bit, denoting whether the
temperature is positive or negative. For Fahrenheit usage, a lookup table or conversion routine must be
used.
Temperature/Data Relationships Table 2
Address
Location
S
2⁶
2⁵
2⁴
2³
2²
2¹
2⁰
02h
MSb
(unit = °C)
2^-1
2^-2
2^-3
2^-4
0
0
LSb
0
0
01h
TEMPERATURE
+120°C
+25.0625°C
+10.125°C
+0.5°C
0°C
-0.5°C
-10.125°C
-25.0625°C
-55°C
DIGITAL OUTPUT
(BINARY)
0111 1000 0000 0000
0001 1001 0001 0000
0000 1010 0010 0000
0000 0000 1000 0000
0000 0000 0000 0000
1111 1111 1000 0000
1111 0101 1110 0000
1110 0110 1111 0000
1100 1001 0000 0000
DIGITAL OUTPUT
(HEX)
7800h
1910h
0A20h
0080h
0000h
FF80h
F5E0h
E6F0h
C900h
OPERATION-Programming
The area of interest in programming the DS1722 is the Configuration register. All programming is done
via the SPI or 3-wire communication interface by selecting the appropriate address of the desired register
location. Table 3 illustrates the addresses for the two registers (configuration and temperature) of the
DS1722.
Register Address Structure Table 3
Read Address
Write Address
00h
80h
01h
No access
02h
No access
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Active Register
Configuration
Temperature LSB
Temperature MSB