Rainbow Electronics DS1822 User Manual
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C
C
8
5
DS1822
FEATURES
• Unique 1-wire interface requires only one
port pin for communication
• Each device has a unique 64-bit serial code
stored in an on-board ROM
• Multi-drop capability simplifies distributed
temperature sensing applications
• Requires no external components
• Can be powered from data line. Power supply
range is 3.0V to 5.5V
• 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
750 ms (max.)
• User-definable nonvolatile alarm settings
• Alarm search command identifies and
addresses devices whose temperature is
outside of programmed limits (temperature
alarm condition)
• Software compatible with the DS18B20
• Applications include thermostatic controls,
industrial systems, consumer products,
thermometers, or any thermally sensitive
system
Econo 1-Wire®Digital Thermomete
PIN ASSIGNMENT
DALLAS
1822
1
2 3
N
N
V
DD
DQ
8-pin 150-mil SOIC
DQ
GND
DD
V
1
2 3
BOTTOM VIEW
TO-92
DS1822
PIN DESCRIPTION
GND - Ground
DQ - Data In/Out
V
- Power Supply Voltage
DD
NC - No Connect
1
DS1822
2
3
4
(DS1822Z)
NC
NC
7
NC
6
GND
DESCRIPTION
The DS1822 Digital Thermometer provides 9 to 12–bit centigrade temperature measurements and has an
alarm function with nonvolatile 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 op eratin g tempera ture ran ge 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 same 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
systems.
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DETAILED PIN DESCRIPTIONS Table 1
V
8-PIN SOIC* TO-92 SYMBOL DESCRIPTION
DS1822
5 1 GND
Ground.
4 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 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 scratchp ad 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 nonvolatile (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 devic es 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 datasheet.
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 c apacitor (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 V
DD
.
DS1822 BLOCK DIAGRAM Figure 1
V
PU
4.7K
DQ
GND
DD
PARASITE POWER
CPP
CIRCUIT
INTERNAL VDD
POWER
SUPPLY
SENSE
64-BIT ROM
AND
1-wire PORT
MEMORY CONTROL
LOGIC
SCRATCHPAD
DS1822
TEMPERATURE SENSOR
ALARM HIGH TRIGGER (T
REGISTER (EEPROM)
ALARM LOW TRIGGER (TL)
REGISTER (EEPROM)
CONFIGURATION REGISTER
(EEPROM)
8-BIT CRC GENERATOR
H
)
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DS1822
OPERATION – MEASUR ING TEMPE RAT URE
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 temperatu re measurement and A-to-D conversion, the
master must issue a Convert T [44h] command. Following the conversion, the resultin g 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” (se e the 1WIRE 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 th e 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 datasheet.
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
LS Byte
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
23 2
2
2
1
2
0
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 2
TEMPERATURE/DATA RELATIONSHIP Table 2
TEMPERATURE DIGITAL OUTPUT
(Binary)
+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
*The power on reset value of the temperature register is +85°C
DIGITAL OUTPUT
(Hex)
5
2
4
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DS1822
OPERATION – ALARM SIG NALING
After the DS1822 performs a temperature conversion, the temperature value is compared to the userdefined 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 nonvolatile (EEPROM) so they will retain data when the
device is powered down. T
and TL can be accessed through b ytes 2 and 3 of the scratchpad as ex plained
H
in the MEMORY section of this datasheet.
TH AND TL REGISTER FORMAT Figure 3
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 b it 0
S 26 2
5
2
5
2
5
2
2
2
1
2
0
Only bits 11 through 4 of the temperature register are used in t he TH and TL comparison since TH and T
L
are 8-bit registers. If the result of a temperature measurement is higher than TH or lower than TL, 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 so me of
the charge is stored on the parasi te 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 1.5 mA. 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 accompl ished 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 10
µs (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 (t
) or data transfer (t
conv
= 10 ms). No other
wr
activity can take place on the 1-wire bus while the pullup is enabled.
The DS1822 can also be powered b y the conventional method of conn ecting an ex ternal power suppl y to
the VDD pin, as shown in Figure 5. The advantage of this method is that the MOSFET pullup is not
required, and the 1–wire bus is free to carry other traffic during the temperature conversion time.
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DS1822
The use of parasite power is not recommended fo r temperatures above 10 0°C since the DS1822 may not
be able to sustain communications due to the hi gher leakage current s that can ex ist at these t emperatures.
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 powe red 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 by a “read time
slot”. 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
Micro-
processor
VPU
4.7K
VPU
1-Wire Bus
DS1822
GND
V
DQ
DD
To Other
1-Wire Devices
POWERING THE DS1822 WITH AN EXTERNAL SUPPLY Figure 5
Micro-
processor
VPU
4.7K
1-Wire Bus
DS1822
GND
V
VDD (External Supply)
DQ
DD
To Other
1-Wire Devices
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 nex t 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-W IRE BUS SYSTEM section
of this datasheet.
64-BIT LASERED ROM CODE Figure 6
8-BIT CRC 48-BIT SERIAL NUMBER 8-BIT FAMILY CODE (22h)
MSB MSB LSB LSB LSBMSB
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DS1822
MEMORY
The DS1822’s memory is organized as shown in Figure 7. The memory consists of an SRAM scratchpad
with nonvolatile 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-onl y. 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 datasheet. Bytes 5, 6 and 7 ar e reserved for internal use by the device and
cannot be overwritten; these bytes will return all 1s when read.
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 cбЦмкЙ=T
SCRATCHPAD (Power-up State)
byte 0 Temperature LSB (50h)
(85°C)
byte 1 Temperature MSB (05h)
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 (0Ch)
byte 7 Reserved (10h)
byte 8 CRC*
*Power-up state depends on value(s) stored
in EEPROM
EEPROM
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