DS1775 Datasheet, PDF (6/13 Pages) Dallas Semiconductor – SOT23-5 Digital Thermometer and Thermostat

DS1775
The only exception is at power–up, in which case the pointer will always be set to 00h, the temperature
register. The pointer address must always proceed data in writing to a register, regardless of which
address is currently selected. Please refer to the “2–Wire Serial Data Bus” section for details of the 2–
wire bus protocol.
Configuration Register Programming
The configuration register is accessed if the DS1775 pointer is currently set to the 01h location. Writing
to or reading from the register is determined by the R/W bit of the 2–wire control byte (See “2–wire
Serial Data Bus” section). Data is read from or written to the configuration register MSb first. The format
of the register is illustrated below in Figure 3. The effect each bit has on DS1775 functionality is
described below along with the power–up state of the bit. The user has read/write access to all bits in the
configuration register. The entire register is volatile, and thus it will power–up in the default state.
Configuration/Status Register Figure 3
0
R1
R0
F1
F0
POL
TM
SD
MSb
LSb
SD = Shutdown bit. If SD is “0”, the DS1775 will continuously perform temperature conversions and
store the last completed result in the thermometer register. If SD is changed to “1”, the conversion in
progress will be completed and stored; then the device will revert to a low–power standby mode. The
O.S. output will be cleared if the device is in the interrupt mode and remain unchanged in the comparator
mode. The 2–wire port remains active. The power–up default state is “0” (continuous conversion mode).
TM = Thermostat mode. If TM=“0”, the DS1775 is in the comparator mode. TM=“1” sets the device to
the interrupt mode. See “OPERATION–Thermostat Control” section for a description of the difference
between the two modes. The power–up default state of the TM bit is “0” (comparator mode).
POL = O.S. Polarity Bit. If POL = “1”, the active state of the O.S. output will be high. A “0” stored in
this location sets the thermostat output to an active low state. The user has read/write access to the POL
bit, and the power–up default state is “0” (active low).
F0, F1 = O.S. Fault Tolerance bits. The fault tolerance defines the number of consecutive conversions
returning a temperature beyond limits is required to set the O.S. output in an active state. This may be
necessary to add margin in noisy environments. Table 4 below defines the four settings. The DS1775 will
power up with F0=F1=“0”, such that a single occurrence will trigger a fault.
Fault Tolerance Configuration Table 4
F1 F0 Consecutive conversions beyond limits to generate fault
00
1
01
2
10
4
11
6
R0, R1 = Thermometer resolution bits. Table 5 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
depicted in the AC Electrical Characteristics. The default state is R0="0" and R1="0" (9–bit conversions).
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