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 ..
DS1825U+ ,Programmable Resolution 1-Wire Digital Thermometer With 4-Bit IDAPPLICATIONS Thermostatic Controls Industrial Systems 1-Wire is a registered trademark of Dallas ..
DS1830 ,Reset Sequence PushbuttonPIN DESCRIPTION- Pushbutton Reset Input1 PBRST2 TD - Time Delay Select Input3 TOL - V Tolerance Sel ..
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
DS1822+ -DS1822Z-DS1822Z+
Econo 1-Wire Digital Thermometer
BENEFITS AND FEATURES • Unique 1-Wire® Interface Requires Only One
Port Pin for Communications Can Be Powered from Data Line Power-Supply Range is 3.0V to 5.5V • Reduced Component Count with Integrated
Temperature Sensor and Interface Requires No External Components Measures temperatures from -55°C to
+125°C (-67°F to +257°F) ±2.0°C Accuracy from -10°C to +85°C Thermometer Resolution is User-Selectable from 9 to 12 Bits Converts Temperature to 12-Bit Digital Word in 750ms (max) • Simplifies Distributed Temperature Sensing
with Multidrop Capability Each Device Has a Unique 64-Bit Serial Code Stored in an On-Board Device Flexible, User-Definable Nonvolatile (NV) Alarm Settings with Alarm Search Command Identifies Devices with Temperatures Outside Programmed Limits Software compatible with the DS18B20 • Applications Include Thermostatic Controls,
Industrial Systems, Consumer Products,
Thermometers, or Any Thermally Sensitive
System
PIN ASSIGNMENT
PIN DESCRIPTION GND - Ground
DQ - Data In/Out
VDD - Power Supply Voltage
NC - No Connect
DESCRIPTION The DS1822 digital thermometer provides 9- to 12-bit centigrade temperature measurements and has an
alarm function with NV user-programmable upper and lower trigger points. The DS1822 communicates
over a 1-Wire bus that by definition requires only one data line (and ground) for communication with a
central microprocessor. It has an operating temperature range of –55°C to +125°C and is accurate to ±2.0°C over the range of –10°C to +85°C. In addition, the DS1822 can derive power directly from the
data line (“parasite power”), eliminating the need for an external power supply.
Each DS1822 has a unique 64-bit serial code, which allows multiple DS1822s to function on the 1-Wire
bus; thus, it is simple to use one microprocessor to control many DS1822s distributed over a large area.
Applications that can benefit from this feature include HVAC environmental controls, temperature
monitoring systems inside buildings, equipment or machinery, and process monitoring and control
1
(BOTTOM VIEW)
2 3
DS1822
Econo 1-Wire Digital
Thermometer 8-Pin 150mil SO
(DS1822Z)
TO-92
(DS1822)
DALLAS
1822 3
NC
NC
NC
NC
GND DQ
VDD
NC
182
DS1822
ORDER INFORMATION
ORDERING
NUMBER
PACKAGE
MARKING
DESCRIPTION DS1822 1822 DS1822 in 3-pin TO92
DS1822/T&R 1822 DS1822 in 3-pin TO92, 2000 Piece Tape-and-Reel
DS1822+ 1822 (See Note) DS1822 in Lead-Free 3-pin TO92
DS1822+T&R 1822 (See Note) DS1822 in Lead-Free 3-pin TO92, 2000 Piece Tape-and-
Reel
DS1822Z DS1822 DS1822 in 150 mil 8-pin SO
DS1822Z/T&R DS1822 DS1822 in 150 mil 8-pin SO, 2500 Piece Tape-and-Reel
DS1822Z+ DS1822 (See Note) DS1822 in Lead-Free 150 mil 8-pin SO
DS1822Z+T&R DS1822 (See Note) DS1822 in Lead-Free 150 mil 8-pin SO, 2500 Piece
Tape-and-Reel
Note: A “+” symbol will also be marked on the package.
DETAILED PIN DESCRIPTIONS Table 1
8-PIN SO* TO-92 SYMBOL DESCRIPTION 1 GND
Ground. 2 DQ
Data Input/Output pin. Open-drain 1-Wire interface pin. Also provides power to the device when used in parasite power mode
(see “Parasite Power” section). 3 VDD
Optional VDD pin. VDD must be grounded for operation in parasite power mode.
*All pins not specified in this table are “No Connect” pins.
OVERVIEW Figure 1 shows a block diagram of the DS1822, and pin descriptions are given in Table 1. The 64-bit
ROM stores the device’s unique serial code. The scratchpad memory contains the 2-byte temperature
register that stores the digital output from the temperature sensor. In addition, the scratchpad provides
access to the 1-byte upper and lower alarm trigger registers (TH and TL), and the 1-byte configuration
register. The configuration register allows the user to set the resolution of the temperature-to-digital
conversion to 9, 10, 11, or 12 bits. The TH, TL and configuration registers are NV (EEPROM), so they will
retain data when the device is powered down.
The DS1822 uses Dallas’ exclusive 1-Wire bus protocol that implements bus communication using one
control signal. The control line requires a weak pullup resistor since all devices are linked to the bus via a
3-state or open-drain port (the DQ pin in the case of the DS1822). In this bus system, the microprocessor
(the master device) identifies and addresses devices on the bus using each device’s unique 64-bit code.
Because each device has a unique code, the number of devices that can be addressed on one bus is
virtually unlimited. The 1-Wire bus protocol, including detailed explanations of the commands and “time
slots,” is covered in the 1-WIRE BUS SYSTEM section of this data sheet.
Another feature of the DS1822 is the ability to operate without an external power supply. Power is instead
supplied through the 1-Wire pullup resistor via the DQ pin when the bus is high. The high bus signal also
charges an internal capacitor (CPP), which then supplies power to the device when the bus is low. This
method of deriving power from the 1-Wire bus is referred to as “parasite power.” As an alternative, the
DS1822 may also be powered by an external supply on VDD.
DS1822
DS1822 BLOCK DIAGRAM Figure 1 VPU
4.7K
POWER
SUPPLY
SENSE
64-BIT ROM
AND
1-wire PORT
DQ
VDD
INTERNAL VDD
CPP
PARASITE POWER
CIRCUIT
MEMORY CONTROL
LOGIC
SCRATCHPAD
8-BIT CRC GENERATOR
TEMPERATURE SENSOR
ALARM HIGH TRIGGER (TH)
REGISTER (EEPROM)
ALARM LOW TRIGGER (TL)
REGISTER (EEPROM)
CONFIGURATION REGISTER
(EEPROM)
GND
DS1822
DS1822
OPERATION—MEASURING TEMPERATURE The core functionality of the DS1822 is its direct-to-digital temperature sensor. The resolution of the
temperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C,
0.25°C, 0.125°C, and 0.0625°C, respectively. The default resolution at power-up is 12 bit. The DS1822
powers-up in a low-power idle state; to initiate a temperature measurement and A-to-D conversion, the
master must issue a Convert T [44h] command. Following the conversion, the resulting thermal data is
stored in the 2-byte temperature register in the scratchpad memory and the DS1822 returns to its idle
state. If the DS1822 is powered by an external supply, the master can issue “read-time slots” (see the 1-
WIRE BUS SYSTEM section) after the Convert T command and the DS1822 will respond by
transmitting 0 while the temperature conversion is in progress and 1 when the conversion is done. If the
DS1822 is powered with parasite power, this notification technique cannot be used since the bus must be
pulled high by a strong pullup during the entire temperature conversion. The bus requirements for parasite
power are explained in detail in the POWERING THE DS1822 section of this data sheet.
The DS1822 output temperature data is calibrated in degrees centigrade; for Fahrenheit applications, a
lookup table or conversion routine must be used. The temperature data is stored as a 16-bit sign-extended
two’s complement number in the temperature register (see Figure 2). The sign bits (S) indicate if the
temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the
DS1822 is configured for 12-bit resolution, all bits in the temperature register will contain valid data. For
11-bit resolution, bit 0 is undefined. For 10-bit resolution, bits 1 and 0 are undefined, and for 9-bit
resolution bits 2, 1 and 0 are undefined. Table 2 gives examples of digital output data and the
corresponding temperature reading for 12-bit resolution conversions.
TEMPERATURE REGISTER FORMAT Figure 2 bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
LS Byte 23 22 21 20 2-1 2-2 2-3 2-4 bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8
MS Byte S S S S S 26 25 24
TEMPERATURE/DATA RELATIONSHIP Table 2
TEMPERATURE DIGITAL OUTPUT
(Binary)
DIGITAL OUTPUT
(Hex) +125°C 0000 0111 1101 0000 07D0h
+85°C* 0000 0101 0101 0000 0550h
+25.0625°C 0000 0001 1001 0001 0191h
+10.125°C 0000 0000 1010 0010 00A2h
+0.5°C 0000 0000 0000 1000 0008h
0°C 0000 0000 0000 0000 0000h
-0.5°C 1111 1111 1111 1000 FFF8h
-10.125°C 1111 1111 0101 1110 FF5Eh
-25.0625°C 1111 1110 0110 1111 FE6Fh
-55°C 1111 1100 1001 0000 FC90h
DS1822
OPERATION—ALARM SIGNALING After the DS1822 performs a temperature conversion, the temperature value is compared to the user-
defined two’s complement alarm trigger values stored in the 1-byte TH and TL registers (see Figure 3).
The sign bit (S) indicates if the value is positive or negative: for positive numbers S = 0 and for negative
numbers S = 1. The TH and TL registers are NV (EEPROM) so they will retain data when the device is
powered down. TH and TL can be accessed through bytes 2 and 3 of the scratchpad as explained in the
MEMORY section of this data sheet.
TH AND TL REGISTER FORMAT Figure 3 bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 26 25 24 23 22 21 20
Only bits 11 through 4 of the temperature register are used in the TH and TL comparison since TH and TL
are 8-bit registers. If the measured temperature is lower than or equal to TL or higher than or equal to TH,
an alarm condition exists and an alarm flag is set inside the DS1822. This flag is updated after every
temperature measurement; therefore, if the alarm condition goes away, the flag will be turned off after the
next temperature conversion.
The master device can check the alarm flag status of all DS1822s on the bus by issuing an Alarm Search
[ECh] command. Any DS1822s with a set alarm flag will respond to the command, so the master can
determine exactly which DS1822s have experienced an alarm condition. If an alarm condition exists and
the TH or TL settings have changed, another temperature conversion should be done to validate the alarm
condition.
POWERING THE DS1822 The DS1822 can be powered by an external supply on the VDD pin, or it can operate in “parasite power”
mode, which allows the DS1822 to function without a local external supply. Parasite power is very useful
for applications that require remote temperature sensing or that are very space constrained. Figure 1
shows the DS1822’s parasite-power control circuitry, which “steals” power from the 1-Wire bus via the
DQ pin when the bus is high. The stolen charge powers the DS1822 while the bus is high, and some of
the charge is stored on the parasite power capacitor (CPP) to provide power when the bus is low. When the
DS1822 is used in parasite power mode, the VDD pin must be connected to ground.
In parasite power mode, the 1-Wire bus and CPP can provide sufficient current to the DS1822 for most
operations as long as the specified timing and voltage requirements are met (refer to the DC
ELECTRICAL CHARACTERISTICS and the AC ELECTRICAL CHARACTERISTICS sections of this
data sheet). However, when the DS1822 is performing temperature conversions or copying data from the
scratchpad memory to EEPROM, the operating current can be as high as 1.5mA. This current can cause
an unacceptable voltage drop across the weak 1-Wire pullup resistor and is more current than can be
supplied by CPP. To assure that the DS1822 has sufficient supply current, it is necessary to provide a
strong pullup on the 1-Wire bus whenever temperature conversions are taking place or data is being
copied from the scratchpad to EEPROM. This can be accomplished by using a MOSFET to pull the bus
directly to the rail as shown in Figure 4. The 1-Wire bus must be switched to the strong pullup within
10µs (max) after a Convert T [44h] or Copy Scratchpad [48h] command is issued, and the bus must be
held high by the pullup for the duration of the conversion (tconv) or data transfer (twr = 10ms). No other
activity can take place on the 1-Wire bus while the pullup is enabled.
The DS1822 can also be powered by the conventional method of connecting an external power supply to
DS1822
The use of parasite power is not recommended for temperatures above 100°C since the DS1822 may not
be able to sustain communications due to the higher leakage currents that can exist at these temperatures.
For applications in which such temperatures are likely, it is strongly recommended that the DS1822 be
powered by an external power supply.
In some situations the bus master may not know whether the DS1822s on the bus are parasite powered or
powered by external supplies. The master needs this information to determine if the strong bus pullup
should be used during temperature conversions. To get this information, the master can issue a Skip ROM
[CCh] command followed by a Read Power Supply [B4h] command followed
During the read time slot, parasite powered DS1822s will pull the bus low, and externally powered
DS1822s will let the bus remain high. If the bus is pulled low, the master knows that it must supply the
strong pullup on the 1-Wire bus during temperature conversions.
SUPPLYING THE PARASITE-POWERED DS1822 DURING TEMPERATURE
CONVERSIONS Figure 4
POWERING THE DS1822 WITH AN EXTERNAL SUPPLY Figure 5
64-BIT LASERED ROM CODE Each DS1822 contains a unique 64–bit code (see Figure 6) stored in ROM. The least significant 8 bits of
the ROM code contain the DS1822’s 1-Wire family code: 22h. The next 48 bits contain a unique serial
number. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is calculated from
the first 56 bits of the ROM code. A detailed explanation of the CRC bits is provided in the CRC
GENERATION section. The 64-bit ROM code and associated ROM function control logic allow the
DS1822 to operate as a 1-Wire device using the protocol detailed in the 1-WIRE BUS SYSTEM section
of this data sheet.
64-BIT LASERED ROM CODE Figure 6
VDD (External Supply) DS1822 GND VDD DQ
VPU
4.7k
To Other
1-Wire Devices 1-Wire Bus
Micro-
processor
VPU
VPU
4.7k
1-Wire Bus
Micro-
processor
DS1822 GND VDD DQ
To Other
1-Wire Devices
DS1822
MEMORY The DS1822’s memory is organized as shown in Figure 7. The memory consists of an SRAM scratchpad
with NV EEPROM storage for the high and low alarm trigger registers (TH and TL) and configuration
register. Note that if the DS1822 alarm function is not used, the TH and TL registers can serve as general-
purpose memory. All memory commands are described in detail in the DS1822 FUNCTION
COMMANDS section.
Byte 0 and byte 1 of the scratchpad contain the LSB and the MSB of the temperature register,
respectively. These bytes are read-only. Bytes 2 and 3 provide access to TH and TL registers. Byte 4
contains the configuration register data, which is explained in detail in the CONFIGURATION
REGISTER section of this data sheet. Bytes 5, 6, and 7 are reserved for internal use by the device and
cannot be overwritten.
Byte 8 of the scratchpad is read-only and contains the cyclic redundancy check (CRC) code for bytes 0
through 7 of the scratchpad. The DS1822 generates this CRC using the method described in the CRC
GENERATION section.
Data is written to bytes 2, 3, and 4 of the scratchpad using the Write Scratchpad [4Eh] command; the data
must be transmitted to the DS1822 starting with the least significant bit of byte 2. To verify data integrity,
the scratchpad can be read (using the Read Scratchpad [BEh] command) after the data is written. When
reading the scratchpad, data is transferred over the 1-Wire bus starting with the least significant bit of
byte 0. To transfer the TH, TL and configuration data from the scratchpad to EEPROM, the master must
issue the Copy Scratchpad [48h] command.
Data in the EEPROM registers is retained when the device is powered down; at power-up the EEPROM
data is reloaded into the corresponding scratchpad locations. Data can also be reloaded from EEPROM to
the scratchpad at any time using the Recall E2 [B8h] command. The master can issue read time slots
following the Recall E2 command and the DS1822 will indicate the status of the recall by transmitting 0
while the recall is in progress and 1 when the recall is done.
DS1822 MEMORY MAP Figure 7 SCRATCHPAD (Power-up State) byte 0 Temperature LSB (50h)
byte 1 Temperature MSB (05h)
EEPROM byte 2 TH Register or User Byte 1* TH Register or User Byte 1
byte 3 TL Register or User Byte 2* TL Register or User Byte 2
byte 4 Configuration Register* Configuration Register
byte 5 Reserved (FFh)
byte 6 Reserved
byte 7 Reserved (10h)
byte 8 CRC*
*Power-up state depends on value(s) stored
in EEPROM
(85°C)
DS1822
CONFIGURATION REGISTER
Byte 4 of the scratchpad memory contains the configuration register, which is organized as
illustrated in Figure 8. The user can set the conversion resolution of the DS1822 using the R0 and R1 bits in this register as shown in Table 3. The power-up default of these bits is R0 = 1 and R1 = 1 (12-bit
resolution). Note that there is a direct tradeoff between resolution and conversion time. Bit 7 and bits 0–4
in the configuration register are reserved for internal use by the device and cannot be overwritten.
CONFIGURATION REGISTER Figure 8 bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 R1 R0 1 1 1 1 1
THERMOMETER RESOLUTION CONFIGURATION Table 3
R1 R0 Resolution Max Conversion Time 0 9-bit 93.75ms (tCONV/8) 1 10-bit 187.5ms (tCONV/4) 0 11-bit 375ms (tCONV/2) 1 12-bit 750ms (tCONV)
CRC GENERATION CRC bytes are provided as part of the DS1822’s 64-bit ROM code and in the 9th byte of the scratchpad
memory. The ROM code CRC is calculated from the first 56 bits of the ROM code and is contained in the
most significant byte of the ROM. The scratchpad CRC is calculated from the data stored in the
scratchpad, and therefore it changes when the data in the scratchpad changes. The CRCs provide the bus
master with a method of data validation when data is read from the DS1822. To verify that data has been
read correctly, the bus master must recalculate the CRC from the received data and then compare this
value to either the ROM code CRC (for ROM reads) or to the scratchpad CRC (for scratchpad reads). If
the calculated CRC matches the read CRC, the data has been received error free. The comparison of CRC
values and the decision to continue with an operation are determined entirely by the bus master. There is
no circuitry inside the DS1822 that prevents a command sequence from proceeding if the DS1822 CRC
(ROM or scratchpad) does not match the value generated by the bus master.
The equivalent polynomial function of the CRC (ROM or scratchpad) is:
CRC = X8 + X5 + X4 + 1
The bus master can recalculate the CRC and compare it to the CRC values from the DS1822 using the
polynomial generator shown in Figure 9. This circuit consists of a shift register and XOR gates, and the
shift register bits are initialized to 0. Starting with the least significant bit of the ROM code or the least
significant bit of byte 0 in the scratchpad, one bit at a time should shifted into the shift register. After
shifting in the 56th bit from the ROM or the most significant bit of byte 7 from the scratchpad, the
polynomial generator will contain the recalculated CRC. Next, the 8-bit ROM code or scratchpad CRC
DS1822
is available in Application Note 27 entitled Understanding and Using Cyclic Redundancy Checks with
Dallas Semiconductor Touch Memory Products.
CRC GENERATOR Figure 9
1-WIRE BUS SYSTEM The 1-Wire bus system uses a single bus master to control one or more slave devices. The DS1822 is
always a slave. When there is only one slave on the bus, the system is referred to as a “single-drop”
system; the system is “multidrop” if there are multiple slaves 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: hardware
configuration, transaction sequence, and 1-Wire signaling (signal types and timing).
HARDWARE CONFIGURATION The 1-Wire bus has by definition only a single data line. Each device (master or slave) 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 the bus is available for use by another device. The 1-Wire port of the
DS1822 (the DQ pin) is open drain with an internal circuit equivalent to that shown in Figure 10.
The 1-Wire bus requires an external pullup resistor of approximately 5 kΩ; 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 480µs,
all components on the bus will be reset.
HARDWARE CONFIGURATION Figure 10 (MSB) (LSB)
XOR XOR XOR
INPUT
VPU
4.7k
5μA
Typ.
RX
TX
DS1822 1-WIRE PORT
100Ω
MOSFET
TX
RX
RX = RECEIVE
TX = TRANSMIT
1-wire Bus
DQ
Pin
DS1822
TRANSACTION SEQUENCE The transaction sequence for accessing the DS1822 is as follows:
Step 1. Initialization
Step 2. ROM Command (followed by any required data exchange)
Step 3. DS1822 Function Command (followed by any required data exchange)
It is very important to follow this sequence every time the DS1822 is accessed, as the DS1822 will not
respond if any steps in the sequence are missing or out of order. Exceptions to this rule are the Search
ROM [F0h] and Alarm Search [ECh] commands. After issuing either of these ROM commands, the
master must return to Step 1 in the sequence.
INITIALIZATION All 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 presence pulse(s) transmitted by the
slave(s). The presence pulse lets the bus master know that slave devices (such as the DS1822) are on the
bus and are ready to operate. Timing for the reset and presence pulses is detailed in the
1-WIRE SIGNALING section.
ROM COMMANDS After the bus master has detected a presence pulse, it can issue a ROM command. These commands
operate on the unique 64–bit ROM codes of each slave device and allow the master to single out a
specific device if many are present on the 1-Wire bus. These commands also allow the master to
determine how many and what types of devices are present on the bus or if any device has experienced an
alarm condition. There are five ROM commands, and each command is 8 bits long. The master device
must issue an appropriate ROM command before issuing a DS1822 function command. A flowchart for
operation of the ROM commands is shown in Figure 11.
SEARCH ROM [F0h] When a system is initially powered up, the master must identify the ROM codes of all slave devices on
the bus, which allows the master to determine the number of slaves and their device types. The master
learns the ROM codes through a process of elimination that requires the master to perform a Search ROM
cycle (i.e., Search ROM command followed by data exchange) as many times as necessary to identify all
of the slave devices. If there is only one slave on the bus, the simpler Read ROM command (see below)
can be used in place of the Search ROM process. For a detailed explanation of the Search ROM
procedure, refer to the iButton Book of Standards at www.ibutton.com/ibuttons/standard.pdf. After every
Search ROM cycle, the bus master must return to Step 1 (Initialization) in the transaction sequence.
READ ROM [33h] This command can only be used when there is one slave on the bus. It allows the bus master to read the
slave’s 64-bit ROM code without using the Search ROM procedure. If this command is used when there
is more than one slave present on the bus, a data collision will occur when all the slaves attempt to
respond at the same time.
MATCH ROM [55h] The match ROM command followed by a 64-bit ROM code sequence allows the bus master to address a
specific slave device on a multidrop or single-drop bus. Only the slave that exactly matches the 64-bit
ROM code sequence will respond to the function command issued by the master; all other slaves on the
bus will wait for a reset pulse.
DS1822
SKIP ROM [CCh] The master can use this command to address all devices on the bus simultaneously without sending out
any ROM code information. For example, the master can make all DS1822s on the bus perform
simultaneous temperature conversions by issuing a Skip ROM command followed by a Convert T [44h]
command.
Note that the Read Scratchpad [BEh] command can follow the Skip ROM command only if there is a
single slave device on the bus. In this case time is saved by allowing the master to read from the slave
without sending the device’s 64-bit ROM code. A Skip ROM command followed by a Read Scratchpad
command will cause a data collision on the bus if there is more than one slave since multiple devices will
attempt to transmit data simultaneously.
ALARM SEARCH [ECh] The operation of this command is identical to the operation of the Search ROM command except that
only slaves with a set alarm flag will respond. This command allows the master device to determine if
any DS1822s experienced an alarm condition during the most recent temperature conversion. After every
Alarm Search cycle (i.e., Alarm Search command followed by data exchange), the bus master must return
to Step 1 (Initialization) in the transaction sequence. Refer to the OPERATION—ALARM SIGNALING
section for an explanation of alarm flag operation.
DS1822 FUNCTION COMMANDS After the bus master has used a ROM command to address the DS1822 with which it wishes to
communicate, the master can issue one of the DS1822 function commands. These commands allow the
master to write to and read from the DS1822’s scratchpad memory, initiate temperature conversions and
determine the power supply mode. The DS1822 function commands, which are described below, are
summarized in Table 4 and illustrated by the flowchart in Figure 12.
CONVERT T [44h] This command initiates a single temperature conversion. Following the conversion, the resulting thermal
data is stored in the 2-byte temperature register in the scratchpad memory and the DS1822 returns to its
low-power idle state. If the device is being used in parasite power mode, within 10µs (max) after this
command is issued the master must enable a strong pullup on the 1-Wire bus for the duration of the
conversion (tconv) as described in the POWERING THE DS1822 section. If the DS1822 is powered by an
external supply, the master can issue read time slots after the Convert T command and the DS1822 will
respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion is
done. In parasite power mode this notification technique cannot be used since the bus is pulled high by
the strong pullup during the conversion.
WRITE SCRATCHPAD [4Eh] This command allows the master to write three bytes of data to the DS1822’s scratchpad. The first data
byte is written into the TH register (byte 2 of the scratchpad), the second byte is written into the TL
register (byte 3), and the third byte is written into the configuration register (byte 4). Data must be
transmitted least significant bit first. All three bytes MUST be written before the master issues a reset, or
the data may be corrupted.
READ SCRATCHPAD [BEh] This command allows the master to read the contents of the scratchpad. The data transfer starts with the
least significant bit of byte 0 and continues through the scratchpad until the 9th byte (byte 8–CRC) is read.
The master may issue a reset to terminate reading at any time if only part of the scratchpad data is needed.
COPY SCRATCHPAD [48h]
