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PDF DS1821 Data sheet ( Hoja de datos )

Número de pieza DS1821
Descripción Programmable Digital Thermostat
Fabricantes Dallas 
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DS1821
Programmable Digital Thermostat
FEATURES
Requires no external components
Measures temperatures from -55°C to +125°C
in 1°C increments. Fahrenheit equivalent is -
67°F to +257°F in 1.8°F increments DS1821
Converts temperature to digital word in 1
second (max.)
Thermostatic settings are user definable and
nonvolatile
Available in 3-pin PR35, TO-220, and 8-pin
SOIC packages
Applications include thermostatic controls,
industrial systems, consumer products,
thermometers, or any thermally sensitive
system
PIN ASSIGNMENT
DS1821
PR35 PACKAGE
See Mech. Drawing
Section
DS1821T
TO-220 PACKAGE
See Mech. Drawing
Section
DQ 1
8 VDD
GND
2
7 NC
NC 3
6 NC
DNC
4
5 DNC
DS1821S 8-Pin SOIC (208-mil)
See Mech Drawings Section
PIN DESCRIPTION
GND
- Ground
DQ - Data In/Out
VDD - Power Supply Voltage +5V
NC - No Connect
DNC
- Do Not Connect
DESCRIPTION
The DS1821 Programmable Digital Thermostat provides a thermal alarm logic output when the
temperature of the device exceeds a user-defined temperature TH. The output remains active until the
temperature drops below user defined temperature TL, allowing for any hysteresis necessary.
User-defined temperature settings are stored in nonvolatile memory, so parts can be programmed prior to
insertion in a system. Communication to/from the DS1821 is accomplished through the DQ pin in a
programming mode; this same pin is used in operation as the thermostat output.
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DS1821 pdf
DS1821
A status register is also present, indicating the status of the thermostatic control, and allowing
configuration of the output polarity as either active high or active low, and establishes the power-up state
of the device.
The status register is defined as follows:
where,
DONE 1
NVB THF TLF T/R POL 1SHOT
DONE = Conversion Done bit. 1 = Conversion complete, 0 = conversion in progress.
THF = Temperature High Flag. This bit will normally be 0, but will be set to 1 when the temperature
exceeds the value of TH. It will remain 1 until reset by writing 0 into this location. This feature provides a
method of determining if the DS1821 has ever been subjected to temperatures above TH. This bit is
nonvolatile, and is stored in E2 memory.
TLF = Temperature Low Flag. This bit will normally be 0, but will be set to 1 when the temperature
is lower than the value of TL. It will remain 1 until reset by writing 0 into this location. This feature
provides a method of determining if the DS1821 has ever been subjected to temperatures below TL. This
bit is nonvolatile, and is stored in E2 memory.
NVB = Nonvolatile memory busy flag. 1 = Write to an E2 memory cell in progress, 0 = nonvolatile
memory is not busy. A write to E2 may take up to 10 ms.
T/R* = Power-up mode bit. If set to a 1, the DS1821 will power up in a thermostat mode. If set to a
0, the device will power up in 1-Wire “read” mode. This bit is nonvolatile.
POL = Output Polarity Bit. 1 = active high, 0 = active low. This bit is nonvolatile.
1SHOT = One-Shot Mode. If 1SHOT is 1, the DS1821 will perform one temperature conversion upon
reception of the Start Convert T protocol. If 1SHOT is 0, the DS1821 will continuously perform
temperature conversions. Note that the One-Shot mode is available only when the device is in 1-Wire
mode. In thermostat mode, the device continuously performs temperature conversions. This bit is
nonvolatile.
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DS1821 arduino
READ/WRITE TIMING DIAGRAM Figure 6
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