DS1775 Datasheet, PDF (7/14 Pages) Dallas Semiconductor – SOT23-5 Digital Thermometer and Thermostat

DS1775
R0, R1 = Thermometer resolution bits. Table 6 defines the resolution of the digital thermometer, based
on the settings of these two bits. There is a direct trade-off between resolution and conversion time, as
shown in the AC Electrical Characteristics. The default state is R0 = 0 and R1 = 0 (9-bit conversions).
Table 6. Thermometer Resolution Configuration
R1
R0
THERMOMETER RESOLUTION
(BITS)
0
0
9
0
1
10
1
0
11
1
1
12
MAX CONVERSION TIME
(SECONDS)
0.1875
0.375
0.75
1.5
Thermostat Setpoints Programming
The thermostat registers (T_OS and T_HYST) can be programmed or read via the 2-wire interface. T_OS is
accessed by setting the DS1775 data pointer to the 03h location, and to the 02h location for T_HYST.
The format of the T_OS and T_HYST registers is identical to that of the Thermometer register; that is, 12-bit
2’s complement representation of the temperature in °C. The user can program the number of bits (9, 10,
11, or 12) for each T_OS and T_HYST that corresponds to the thermometer resolution mode chosen. For
example, if the 9-bit mode is chosen the three least significant bits of T_OS and T_HYST are ignored by the
thermostat comparator. Table 7 shows the format for both T_OS and T_HYST. The power-up default for T_OS is
+80°C and for T_HYST is +75°C.
Table 7. Thermostat Setpoint (T_OS/T_HYST) Format
S
2⁶
2⁵
2⁴
2³
2²
MSb
(UNIT = °C)
2^-1
2^-2
2^-3
2^-4
0
0
2¹
2⁰
MSB
LSb
0
0
LSB
TEMPERATURE
(°C)
+80
+75
+10.125
+0.5
0
-0.5
-10.125
-25.0625
-55
DIGITAL OUTPUT
(BINARY)
0101 0000 0000 0000
0100 1011 0000 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)
5000h
4B00h
0A20h
0080h
0000h
FF80h
F5E0h
E6F0h
C900h
If the user does not wish to take advantage of the thermostat capabilities of the DS1775, the 24 bits can be
used for general storage of system data that need not be maintained following a power loss.
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