Datasheet

Operation—Thermostat Function
The thermostat output (T
OUT
) is updated after every
temperature conversion, based on a comparison between
the measured digital temperature and user-defined upper
and lower thermostat trip points. T
OUT
remains at the
updated value until the next conversion completes. When
the measured temperature meets or exceeds the value
stored in the upper trip-point register (T
H
), T
OUT
becomes
active and remains active until the measured temperature
falls below the value stored in the lower trip-point register
(T
L
) (see Figure 5). This allows the user to program any
amount of hysteresis into the output response. The active
state of T
OUT
is user-programmable through the polarity
bit (POL) in the configuration register.
The user-defined values in the T
H
and T
L
registers (see
Figure 4) must be in two’s complement format with the
MSb (bit 15) containing the sign bit (S). The T
H
and T
L
resolution is determined by the R0 and R1 bits in the
configuration register (see Table 6), so the T
H
and T
L
resolution matches the output temperature resolution. For
example, for 10-bit resolution bits 5 through 0 of the T
H
and T
L
registers read out as 0 (even if 1s are written to
these bits), and the converted temperature is compared
to the 10 MSbs of T
H
and T
L
.
The T
H
and T
L
registers are stored in EEPROM; there-
fore, they are NV and can be programmed prior to device
installation. Writing to and reading from the T
H
and T
L
registers is achieved using the Access T
H
and Access
T
L
commands. When making changes to the T
H
and T
L
registers, conversions should first be stopped using the
Stop Convert T command if the device is in continuous
conversion mode. Note that if the thermostat function is
not used, the T
H
and T
L
registers can be used as general-
purpose NV memory.
Another thermostat feature is the temperature high and
low flags (THF and TLF) in the configuration register.
These bits provide a record of whether the temperature
has been greater than T
H
or less than T
L
at anytime since
the device was powered up. These bits power up as 0s,
and if the temperature ever exceeds the T
H
register value,
the THF bit is set to 1, or if the temperature ever falls
below the T
L
value, the TLF bit is set to 1. Once THF and/
or TLF has been set, it remains set until overwritten with a
0 by the user or until the power is cycled.
Ds1631A Stand-Alone
Thermostat Operation
Since the DS1631A automatically begins taking tem-
perature measurements at power-up, it can function as
a standalone thermostat (i.e., it can provide thermostatic
operation without microcontroller communication). For
standalone operation, the NV T
H
and T
L
registers and the
POL and 1SHOT bits in the configuration register should
be programmed to the desired values prior to installation.
Since the default conversion resolution at power-up is 12
bits (R1 = 1 and R0 = 1 in the configuration register), the
conversion resolution is always 12 bits during standalone
thermostat operation.
Conguration Register
The configuration register allows the user to program
various DS1631 options such as conversion resolution,
TOUT polarity, and operating mode. It also provides infor-
mation to the user about conversion status, EEPROM
activity, and thermostat activity. The configuration register
is arranged as shown in Figure 6 and detailed descrip-
tions of each bit are provided in Table 5. This register
can be read from and written to using the Access Config
command. When writing to the configuration register, con-
versions should first be stopped using the Stop Convert T
command if the device is in continuous conversion mode.
Note that the POL and 1SHOT bits are stored in EEPROM
so they can be programmed prior to installation is desired.
All other configuration register bits are SRAM and power
up in the state shown in Table 5.
Figure 5. Thermostat Output Operation
Figure 6. Configuration Register
T
L
TEMP
T
OUT
POL = 1 (T
OUT
IS ACTIVE HIGH)
T
H
LOGIC 1
LOGIC 0
MSB BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 LSB
DONE THF TLF NVB R1 R0 POL* 1SHOT*
*NV (EEPROM)
DS1631/DS1631A/
DS1731
High-Precision Digital
Thermometer and Thermostat
www.maximintegrated.com
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