DS18S20-PAR Datasheet PDF - Dallas Semiconductor
| Part Number | DS18S20-PAR | |
| Description | Parasite-Power Digital Thermometer | |
| Manufacturers | Dallas Semiconductor | |
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FEATURES
• Unique 1-wire interface requires only one
port pin for communication
• Derives power from data line (“parasite
power”)—does not need a local power supply
• Multi-drop capability simplifies distributed
temperature sensing applications
• Requires no external components
• ±0.5°C accuracy from –10°C to +85°C
• Measures temperatures from –55°C to
+100°C (–67°F to +212°F)
• 9-bit thermometer resolution
• Converts temperature in 750 ms (max.)
• User–definable non-volatile temperature
alarm settings
• Alarm search command identifies and
addresses devices whose temperature is
outside of programmed limits (temperature
alarm condition)
• Ideal for use in remote sensing applications
(e.g., temperature probes) that do not have a
local power source
DS18S20-PAR
1-Wire® Parasite-Power
Digital Thermometer
PIN ASSIGNMENT
DALLAS
18S20P
123
123
(BOTTOM VIEW)
TO-92
(DS18S20-PAR)
PIN DESCRIPTION
GND - Ground
DQ - Data In/Out
NC - No Connect
DESCRIPTION
The DS18S20-PAR digital thermometer provides 9–bit centigrade temperature measurements and has an
alarm function with nonvolatile user-programmable upper and lower trigger points. The DS18S20-PAR
does not need an external power supply because it derives power directly from the data line (“parasite
power”). The DS18S20-PAR communicates over a 1-wire bus, which 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 +100°C and is accurate to ±0.5°C over a range of –10°C to +85°C.
Each DS18S20-PAR has a unique 64-bit identification code, which allows multiple DS18S20-PARs to
function on the same 1–wire bus; thus, it is simple to use one microprocessor to control many
DS18S20-PARs 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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DS18S20-PAR
The master device can check the alarm flag status of all DS DS18S20-PARs on the bus by issuing an
Alarm Search [ECh] command. Any DS18S20-PARs with a set alarm flag will respond to the command,
so the master can determine exactly which DS18S20-PARs 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.
64-BIT LASERED ROM CODE
Each DS18S20-PAR contains a unique 64–bit code (see Figure 5) stored in ROM. The least significant 8
bits of the ROM code contain the DS18S20-PAR’s 1–wire family code: 10h. 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 DS18S20-PAR to operate as a 1–wire device using the protocol detailed in the 1-WIRE BUS
SYSTEM section of this datasheet.
64-BIT LASERED ROM CODE Figure 5
8-BIT CRC
48-BIT SERIAL NUMBER
8-BIT FAMILY CODE (10h)
MSB
LSB MSB
LSB MSB
LSB
MEMORY
The DS18S20-PAR’s memory is organized as shown in Figure 6. The memory consists of an SRAM
scratchpad with nonvolatile EEPROM storage for the high and low alarm trigger registers (TH and TL).
Note that if the DS18S20-PAR 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 DS18S20-PAR 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. Bytes 4
and 5 are reserved for internal use by the device and cannot be overwritten; these bytes will return all 1s
when read. Bytes 6 and 7 contain the COUNT REMAIN and COUNT PER ºC registers, which can be
used to calculate extended resolution results as explained in the OPERATION – MEASURING
TEMPERATURE section. 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 DS18S20-PAR generates this CRC using
the method described in the CRC GENERATION section.
Data is written to bytes 2 and 3 of the scratchpad using the Write Scratchpad [4Eh] command; the data
must be transmitted to the DS18S20-PAR 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 and TL 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”
(see the 1-WIRE BUS SYSTEM section) following the Recall E2 command and the DS18S20-PAR will
indicate the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is
done.
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