Datasheet

DS1775
7 of 14
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)
MAX CONVERSION TIME
(SECONDS)
0
0
9
0.1875
0
1
10
0.375
1
0
11
0.75
1
1
12
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
2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSB
MSb
(UNIT = °C)
LSb
2
-1
2
-2
2
-3
2
-4
0
0
0
0
LSB
TEMPERATURE
(°C)
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
+80
0101 0000 0000 0000
5000h
+75
0100 1011 0000 0000
4B00h
+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
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.