DS75_08 Datasheet, PDF (7/14 Pages) Dallas Semiconductor – Digital Thermometer and Thermostat

Figure 3. TEMPERATURE, T_H, and T_L REGISTER FORMAT
bit 15
bit 14
bit 13
bit 12
bit 11
bit 10
bit 9
MS Byte
S
2⁶
2⁵
2⁴
2³
2²
2¹
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
LS Byte
2^-1
2^-2
2^-3
2^-4
0
0
0
DS75
bit 8
2⁰
bit 0
0
Table 3. 12-BIT RESOLUTION TEMPERATURE/DATA RELATIONSHIP
TEMPERATURE
(°C)
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
+125
0111 1101 0000 0000
7D00h
+25.0625
0001 1001 0001 0000
1910h
+10.125
0000 1010 0010 0000
0A20h
+0.5
0000 0000 1000 0000
0080h
0
0000 0000 0000 0000
0000h
-0.5
1111 1111 1000 0000
FF80h
-10.125
1111 0101 1110 0000
F5E0h
-25.0625
1110 0110 1111 0000
E6F0h
-55
1100 1001 0000 0000
C900h
SHUTDOWN MODE
For power-sensitive applications, the DS75 offers a low-power shutdown mode. The SD bit in the
configuration register controls shutdown mode. When SD is changed to 1, the conversion in progress
will be completed and the result stored in the temperature register after which the DS75 will go into a
low-power standby state. The O.S. output will be cleared if the thermostat is operating in interrupt mode
and O.S will remain unchanged in comparator mode. The 2-wire interface remains operational in
shutdown mode, and writing a 0 to the SD bit returns the DS75 to normal operation.
OPERATION–THERMOSTAT
The DS75 thermostat has two operating modes, comparator mode and interrupt mode, which activate and
deactivate the open-drain thermostat output (O.S.) based on user-programmable trip-points (T_OS and
T_HYST). The DS75 powers up with the thermostat in comparator mode with active-low O.S. polarity and
with the over-temperature trip-point (T_OS) register set to 80°C and the hysteresis trip-point (T_HYST)
register set to 75°C. If these power-up settings are compatible with the application, the DS75 can be used
as a standalone thermostat (i.e., no 2–wire communication required). If interrupt mode operation, active-
high O.S. polarity or different T_OS and T_HYST values are desired, they must be programmed after power-
up, so standalone operation is not possible.
In both operating modes, the user can program the thermostat fault tolerance, which sets how many
consecutive temperature readings (1, 2, 4, or 6) must fall outside of the thermostat limits before the
thermostat output is triggered. The fault tolerance is set by the F1 and F0 bits in the configuration and at
power-up the fault tolerance is 1.
The data format of the T_OS and T_HYST registers is identical to that of the temperature register (see Figure
3), i.e., a two-byte two’s complement representation of the trip-point temperature in degrees centigrade
with bits 3 through 0 hardwired to 0. After every temperature conversion, the measured temperature is
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