DS1821S ,Programmable Digital Thermostatpin descriptions are given in Table 1. The DS1821can operate as a standalone thermostat with user- ..
DS1822 ,Econo 1-Wire Digital Thermometerpin descriptions are given in Table 1. The 64-bit ROM stores the device’s unique serial code. The s ..
DS1822+ ,Econo 1-Wire Digital ThermometerApplications that can benefit from this feature include HVAC environmental controls, temperature mo ..
DS1822Z ,Econo 1-Wire Digital Thermometerpin descriptions are given in Table 1. The 64-bit ROM stores the device’s unique serial code. The s ..
DS1822Z+ ,Econo 1-Wire Digital ThermometerApplications Include Thermostatic Controls, DQ - Data In/Out Industrial Systems, Consumer Products, ..
DS1825 ,Programmable Resolution 1-Wire Digital Thermometer With 4-Bit IDELECTRICAL CHARACTERISTICS (-55°C to +125°C; V = 3.0V to 3.7V) DDPARAMETER SYMBOL CONDITION M ..
DZ23C10 ,Zener DiodesDZ23C2V7–DZ23C51Vishay Telefunken300 mW Dual Surface Mount Zener Diodes
DZ23C15-7-F , 300mW DUAL SURFACE MOUNT ZENER DIODE
DZ23C16-7-F , 300mW DUAL SURFACE MOUNT ZENER DIODE
DZ23C18 ,Zener DiodesAbsolute Maximum RatingsT = 25
DS1821S
Programmable Digital Thermostat and Thermometer
FEATURESRequires no external componentsUnique 1-Wire® interface requires only one
port pin for communicationOperates over a -55°C to +125°C (67°F to
+257°F) temperature rangeFunctions as a standalone thermostat with
user-definable trip-pointsProvides 8-bit (1°C resolution) centigradetemperature measurementsAccuracy is �1�C over 0°C to +85°C rangeConverts temperature to a digital word in 1
second (max)Available in 3-pin PR35 and 8-pin SOICpackagesApplications include thermostatic controls,
industrial systems, consumer products,
thermometers, or any thermally sensitivesystem
PIN ASSIGNMENT
PIN DESCRIPTIONGND- Ground- Data In/Out and Thermostat Output
VDD- Power Supply Voltage- No Connect
DESCRIPTIONThe DS1821 can function as a standalone thermostat with user-programmable trip-points or as 8-bittemperature sensor with a 1-wire digital interface. The thermostat trip-points are stored in nonvolatilememory, so DS1821 units can be programmed prior to system insertion for true standalone operation.The DS1821 has an operating temperature range of –55°C to +125°C and is accurate to �1�C over a rangeof 0°C to +85°C. Communication with the DS1821 is accomplished through the open-drain DQ pin; thispin also serves as the thermostat output.
DS1821Programmable Digital Thermostat and8-pin 208-mil SOIC
PR35
(DS1821)
VDD
DS1821
DETAILED PIN DESCRIPTIONS Table 1*All pins not specified in this table are “No Connect” pins.
OVERVIEWFigure 1 shows a block diagram of the DS1821 and pin descriptions are given in Table 1. The DS1821
can operate as a standalone thermostat with user-programmable trip-points or as 8-bit temperature sensor
with a 1-wire digital interface. The open-drain DQ pin functions as the thermostat output for thermostat
operation and as the data I/O pin for 1-wire communications. The 1-wire interface provides user access to
the nonvolatile (EEPROM) thermostat trip-point registers (TH and TL), the status/configuration register,
and the temperature register.
When configured as standalone thermostat, temperature conversions start immediately at power-up. In
this mode, the DQ pin becomes active when the temperature of the DS1821 exceeds the limit
programmed into the TH register, and remains active until the temperature drops below the limit
programmed into the TL register.
The DS1821 uses Dallas’ exclusive 1-wire bus protocol that implements bus communication with one
control signal. This system is explained in detail in the 1-WIRE BUS SYSTEM section of this datasheet.
DS1821 BLOCK DIAGRAM Figure 1
TEMPERATURE SENSOR FUNCTIONALITYThe core functionality of the DS1821 is its proprietary direct-to-digital temperature sensor, which
provides 8-bit (1°C increment) centigrade temperature readings over the range of -55°C to +125°C.
VDD
4.7K
GND
DS1821
counter is preset with a base count that corresponds to –55�C. If the counter reaches 0 before the gate
period is over, the temperature register, which is preset to –55�C, is incremented by one degree, and the
counter is again preset with a starting value determined by the slope accumulator circuitry. The presetcounter value is unique for every temperature increment and compensates for the parabolic behavior of
the oscillators over temperature.
At this time, the counter is clocked again until it reaches 0. If the gate period is not over when the counter
reaches 0, the temperature register is incremented again. This process of presetting the counter, counting
down to zero, and incrementing the temperature register is repeated until the counter takes less time toreach zero than the duration of the gate period of the high temp-co oscillator. When this iterative process
is complete, the value in the temperature register will indicate the centigrade temperature of the device.
TEMPERATURE MEASURING CIRCUITRY Figure 2
OPERATING MODESThe DS1821 has two operating modes: 1-wire mode and thermostat mode. The power-up operating mode
is determined by the user-programmable T/R･ bit in the status/configuration register: if T/R･ = 0 the device
powers-up in 1-wire mode, and if T/R･ = 1 the device powers-up in thermostat mode. The T/R･ bit is
stored in nonvolatile memory (EEPROM), so it will retain its value when the device is powered down.
1-WIRE MODE
DS1821
the 1-WIRE BUS SYSTEM section of this datasheet. These communications can include reading and
writing the high and low thermostat trip-point registers (TH and TL) and the configuration register, and
reading the temperature, counter, and slope accumulator registers. Also in this mode, the microprocessor
can initiate and stop temperature measurements as described in the OPERATION – MEASURINGTEMPERATURE section of this datasheet.
The TH and TL registers and certain bits (THF, TLF, T/R･, POL and 1SHOT) in the status/configuration
register are stored in nonvolatile EEPROM memory, so they will retain data when the device is powered
down. This allows these registers to be pre-programmed when the DS1821 is to be used as a standalone
thermostat. Writes to these nonvolatile registers can take up to 10ms. To avoid data corruption, nowrites to nonvolatile memory should be initiated while a write to nonvolatile memory is in progress.
Nonvolatile write status can be monitored by reading the NVB bit in the status/configuration register:
NVB = 0 – a write to EEPROM memory is in progress, NVB = 0 – nonvolatile memory is idle.
THERMOSTAT MODEIn thermostat mode (T/R･ = 1), the DS1821 can operate as a standalone thermostat that triggers according
to the TH and TL trip-points programmed while the device was in 1-wire mode. In thermostat mode theDS1821 powers-up performing continuous temperature conversions, and the DQ pin acts as the
thermostat output. Detailed operation of the thermostat output is provided in the OPERATION –
STANDALONE THERMOSTAT section of this datasheet.
Communications can be re-establish with the DS1821 while it is in thermostat mode by pulling VDD to 0V
while the DQ line is held high, and then toggling the DQ line low 16 times as shown in Figure 12. This
temporarily places the DS1821 in 1-wire mode, allowing microprocessor communication with the
DS1821 via the DQ pin. At this time any I/O function can be performed, such as reading/writing the TH,
TL or configuration registers or reading the temperature register. To return to thermostat mode, the same
procedure can be performed (pulling VDD to 0V while the DQ line is held high, and then clocking the DQ
line 16 times) or the power can be cycled. Note that temporarily putting the DS1821 into 1-wire mode
does not change the power-up mode of the device; this can only be changed by rewriting the T/R･ bit in
the status/configuration register. Also note that holding both VDD and DQ low for more than
approximately 10 seconds will cause the DS1821 to be powered down.
OPERATION – MEASURING TEMPERATUREDS1821 output temperature data is calibrated in degrees centigrade and is stored in two’s complement
format in the 1-byte (8-bit) temperature register (see Figure 3), which the user can access when theDS1821 is in 1-wire mode (T/R･ = 0 in the status/configuration register). The sign bit (S) indicates if the
temperature is positive or negative; for positive numbers S = 0 and for negative numbers S = 1. Table 2
gives examples of digital output data and the corresponding temperature reading. For Fahrenheit
measurements, a lookup table or conversion routine must be used.
The DS1821 can be configured by the user to take continuous temperature measurements (continuousconversion mode) or single measurements (one-shot mode). The desired configuration can be achieved
by setting the nonvolatile1SHOT bit in the status/configuration register: 1SHOT = 0 – continuous
conversion mode, 1SHOT = 1 – one-shot mode. Note that the 1SHOT setting only controls the operation
of the device in 1-wire mode; in thermostat mode, continuous temperature conversions are started
automatically at power-up.
In continuous conversion mode, the Start Convert T [EEh] command initiates continuous temperatureconversions, which can be stopped using the Stop Convert T [22h] command. In one-shot mode the Start
DS1821
configuration register to determine when the conversion status: DONE = 0 ― conversion in progress,
DONE = 1 ― conversion complete. The DONE bit does not provide conversion status in continuous
conversion mode since measurements are constantly in progress (i.e., DONE will always be 0).
TEMPERATURE, TH and TL REGISTER FORMAT Figure 3bit 7bit 6bit 5bit 4bit 3bit 2bit 1bit 0
TEMPERATURE/DATA RELATIONSHIP Table 2
HIGH-RESOLUTION TEMPERATURE READINGSThe user can calculate temperature values with higher than 8-bit resolution using the data remaining inthe counter and slope accumulator when the temperature conversion is complete. To do this the user must
first read the temperature from the 8-bit temperature register. This value is called TEMP_READ in the
high-resolution equation (see Eq. 1). The 9-bit counter value must then be obtained by issuing the Read
Counter [A0h] command. This value is the count remaining in the counter at the end of the gate period
and is called COUNT_REMAIN in Eq. 1. Next the Load Counter [41h] command must be issued, whichloads the 9-bit slope accumulator value into the counter register. The slope accumulator value (called
COUNT_PER_C in Eq. 1) can then be read from the counter by again issuing the Read Counter [A0h]
command. The slope accumulator value is called “COUNT_PER_C” because it represents the number of
counts needed for an accurate measurement at a given temperature (i.e., the counts per degree C). The
high-resolution temperature can then be calculated using Eq. 1:
Eq. 1)TEMPERATURE = TEMP_READ � 0.5 + CPERCOUNT_
Additional information about high-resolution temperature calculations can be found in Application Note
105: “High Resolution Temperature Measurement with Dallas Direct-to-Digital Temperature Sensors”.
DS1821
OPERATION – THERMOSTATWhen the DS1821 is in thermostat mode (T/R･ = 1 in the status/configuration register), temperature
conversions are performed continuously beginning at power-up (regardless of the value of the 1SHOT
bit), and the DQ pin serves as the thermostat output. The DQ output will become active when the
temperature of the DS1821 exceeds the user-defined limit in the TH register, and will remain active until
the temperature drops below the user-defined limit in the TL register as illustrated in Figure 4. Thus, the
user can select TH and TL to provide the desired amount of thermostat output hysteresis.
The user-defined 8-bit centigrade trip-point values (TH and TL) must be stored in two’s complement
format as shown in Figure 3. The sign bit (S) indicates if the temperature is positive or negative; for
positive numbers S = 0 and for negative numbers S = 1. The non-volatile TH and TL registers must be
programmed when the DS1821 is in 1-wire mode as explained in the OPERATING MODES section of
this datasheet. The DS1821 can be temporarily switched from thermostat mode to 1-wire mode to changethe TH and TL values as also explained in the OPERATING MODES section.
The polarity (i.e., the active state) of the DQ output is user-selectable with the nonvolatile POL bit in the
status/configuration register. DQ is active-high when POL = 1, and DQ is active-low when POL = 0.
Two bits in the status/configuration register, THF and TLF, provide additional thermostatic information.
The value of these bits is normally 0. The THF (temperature high flag) bit will be set to 1 if the measuredtemperature is ever greater than the value in the TH register and will remain a 1 until the user rewrites the
bit with a 0. The THL (temperature low flag) bit will be set to 1 if the temperature is ever lower than the
value in the TL register and will remain a 1 until the user rewrites the bit with a 0. These bits provide a
record of the device temperature relative to the thermostat trip-points over a period of time. They are
stored in nonvolatile memory, so the data stored in THF and TLF can be analyzed after any number ofpower cycles. The THF and THL bits function in both 1-wire and thermostat mode.
DQ OPERATION IN THERMOSTATE MODE Figure 4
STATUS/CONFIGURATION REGISTERThe status/configuration register provides information to the user about conversion status, EEPROM
activity and thermostat activity. It also allows the user to program various DS1821 options such as
power-up operating mode, thermostat output polarity and conversion mode. The status/configuration
register is arranged as shown in Figure 5 and detailed descriptions of each bit are provided in Table 3.
Note that the THF, THL T/R･, POL and 1SHOT bits are stored in nonvolatile memory (EEPROM).
CONFIGURATION REGISTER Figure 5bit 7bit 6bit 5bit 4bit 3bit 2bit 1bit 0THTemp (°C)
Operating Mode = Thermostat
DS1821
CONFIGURATION REGISTER BIT DESCRIPTIONS Table 3*Stored in EEPROM
DS1821
1-WIRE BUS SYSTEMThe 1-wire bus system uses a single bus master (i.e., a microprocessor) to control slave devices. The
DS1821 functions as a slave device when it is used in 1-wire mode; however, since the DS1821 is not
addressable or multi-droppable, a single 1-wire-mode DS1821 must be the only slave device on the bus.
All data and commands are transmitted least significant bit first over the 1-wire bus.
The following discussion of the 1-wire bus system is broken down into three topics: hardwareconfiguration, transaction sequence, and 1-wire signaling (signal types and timing).
HARDWARE CONFIGURATIONThe 1-wire bus has by definition only a single data line. Each device (in this case, the master and one
DS1821) interfaces to the data line via an open drain or 3–state port. This allows each device to “release”
the data line when the device is not transmitting data so that the bus is available for use by the other
device. The 1-wire port of the DS1821 (the DQ pin) is open drain with an internal circuit equivalent tothat shown in Figure 6.
The 1-wire bus requires an external pullup resistor of approximately 5 k�; thus, the idle state for the 1-
wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be left in the idle
state if the transaction is to resume. Infinite recovery time can occur between bits so long as the 1-wire
bus is in the inactive (high) state during the recovery period. If the bus is held low for more than 480 �s,
the DS1821 will be reset.
HARDWARE CONFIGURATION Figure 6
TRANSACTION SEQUENCEThe transaction sequence for accessing the DS1821 via the 1-wire port is as follows:InitializationDS1821 Function Command
DS1821
INITIALIZATIONAll transactions on the 1-wire bus begin with an initialization sequence. The initialization sequence
consists of a reset pulse transmitted by the bus master followed by a presence pulse transmitted by the
DS1821. The presence pulse lets the bus master know that the DS1821 is on the bus and ready to
operate. Timing for the reset and presence pulses is detailed in the 1-WIRE SIGNALING section.
DS1821 FUNCTION COMMANDSThe DS1821 function commands in this section allow the master to communicate with and configure theDS1821. The DS1821 function commands are summarized in Table 4.
READ TEMPERATURE [AAh]Provides read access to the 1-byte temperature register.
START CONVERT T [EEh]Initiates temperature conversions. If the part is in one-shot mode (1SHOT = 1), only one conversion will
be performed. If it is in continuous mode (1SHOT = 0), continuous conversions will be performed until a
Stop Convert T command is received.
STOP CONVERT T [22h]Stops temperature conversions when the device is in continuous conversion mode (1SHOT = 0). This
opcode has no function if the device is in one-shot mode (1SHOT = 1).
WRITE TH [01h]WRITE TL [02h]Provides write access to the 8-bit TH and TL registers, respectively.
READ TH [A1h]
READ TL [A2h]Provides read access to the 8-bit TH and TL registers, respectively.
WRITE STATUS [0Ch]Provides write access to the 8-bit status/configuration register.
READ STATUS [ACh]Provides read access to the 8-bit status/configuration register.
READ COUNTER [A0h]Provides read access to data in the 9-bit counter register for use in high-resolution temperature
calculations. This is explained in detail in the HIGH-RESOLUTION TEMPERATURE READINGS
section.
LOAD COUNTER [41h]Loads the 9-bit data from the slope accumulator register into the counter register so that it can be accessed
using the Read Counter [A0h] command. Use of the Load Counter command is explained in detail in the
HIGH-RESOLUTION TEMPERATURE READINGS section.
