DS75 Datasheet, PDF (7/13 Pages) Dallas Semiconductor – 2.Wire Thermal Watchdog

DS75
Thermometer Resolution Configuration
Table 5
R1 R0 Thermometer Max Conversion
Resolution
Time
00
9–bit
0.15s
01
10–bit
0.3s
10
11–bit
0.6s
11
12–bit
1.2s
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 DS75 data pointer to the 03h location, and that for the T_HYST setting is 02h.
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 correspond to the thermometer resolution mode chosen. If the 9–bit
mode is chosen, for example, the 3 least significant bits of T_OS and T_HYST will be ignored by the
thermostat comparator. The format for both T_OS and T_HYST is shown below in Table 6. The power–up
default of T_OS is 80°C and that for T_HYST is 75°C.
Thermostat Setpoint (TOS/THYST) Format
Table 6
S
2⁶
2⁵
2⁴
2³
2²
2¹
2⁰ MSB
MSb
(UNIT = °C)
2^–1
2^–2
2^–3
2^–4
0
0
LSb
0
0 LSB
TEMPERATURE/DATA RELATIONSHIPS
DIGITAL
DIGITAL OUTPUT OUTPUT
TEMP
(Binary)
(Hex)
+80°C
0101 0000 0000 0000
5000h
+75°C
0100 1011 0000 0000
4B00h
+10.125°C 0000 1010 0010 0000
0A20h
+0.5°C
00000000 1000 0000
0080h
+0°C
00000000 0000 0000
0000h
–0.5°C
1111 1111 1000 0000
FF80h
–10.125°C 1111 0101 1110 0000
E5E0h
–25.0625°C 1110 0110 1111 0000
E6F0h
–55°C
1100 1001 0000 0000
C900h
If the user does not wish to take advantage of the thermostat capabilities of the DS75, the 24 bits can be
used for general storage of system data that need not be maintained following a power loss. The O.S.
output should be left floating if this is done.
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