DS1775 Datasheet, PDF (6/14 Pages) Dallas Semiconductor – SOT23-5 Digital Thermometer and Thermostat

DS1775
temperature register. The pointer address must always precede data in writing to a register, regardless of
which address is currently selected. See 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 the 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 in Table 4. 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 powers up in the default state.
Table 4. Configuration/Status Register
0
R1
R0
F1
MSb
F0
POL
TM
SD
LSb
SD = Shutdown bit. If SD is 0, the DS1775 continuously performs temperature conversions and stores
the last completed result in the thermometer register. If SD is changed to 1, the conversion in progress is
completed and stored; then the device reverts to a low-power standby mode. The O.S. output is cleared if
the device is in the interrupt mode and remains 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 the 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 is 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 5 defines the four settings. The DS1775 powers up
with F0 = F1 = 0, such that a single occurrence triggers a fault.
Table 5. Fault Tolerance Configuration
F1
F0
CONSECUTIVE CONVERSIONS BEYOND LIMITS
TO GENERATE FAULT
00
1
01
2
10
4
11
6
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