Rainbow Electronics DS1722 - Manual (Page 4)

DS1722
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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 2
6
2
5
2
4
2
3
2
2
2
1
2
0
02h
MSb (unit =
°
C) LSb
2
-1
2
-2
2
-3
2
-4
0 0 0 0 01h
TEMPERATURE
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
+120
°
C 0111 1000 0000 0000 7800h
+25.0625
°
C 0001 1001 0001 0000 1910h
+10.125
°
C 0000 1010 0010 0000 0A20h
+0.5
°
C 0000 0000 1000 0000 0080h
0
°
C 0000 0000 0000 0000 0000h
-0.5
°
C 1111 1111 1000 0000 FF80h
-10.125
°
C 1111 0101 1110 0000 F5E0h
-25.0625
°
C 1110 0110 1111 0000 E6F0h
-55
°
C 1100 1001 0000 0000 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 Active Register
00h 80h Configuration
01h No access Temperature LSB
02h No access Temperature MSB