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PDF 18B20 Data sheet ( Hoja de datos )
| Número de pieza | 18B20 | |
| Descripción | DS18B20 | |
| Fabricantes | Dallas Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de 18B20 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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• 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)
• ±0.5°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 DS1822
• Applications include thermostatic controls,
industrial systems, consumer products,
thermometers, or any thermally sensitive
system
DS18B20
Programmable Resolution
1-Wire® Digital Thermometer
PIN ASSIGNMENT
DALLAS
18B20
123
NC 1
8 NC
NC 2
7 NC
VDD
3
6 NC
DQ 4
5 GND
8-pin 150-mil SOIC
(DS18B20Z)
12 3
(BOTTOM VIEW)
TO-92
(DS18B20)
PIN DESCRIPTION
GND - Ground
DQ - Data In/Out
VDD - Power Supply Voltage
NC - No Connect
DESCRIPTION
The DS18B20 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 DS18B20
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 ±0.5°C over the range of –10°C to +85°C. In addition, the DS18B20 can derive power
directly from the data line (“parasite power”), eliminating the need for an external power supply.
Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same
1–wire bus; thus, it is simple to use one microprocessor to control many DS18B20s 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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043001
1 page  
DS18B20
The use of parasite power is not recommended for temperatures above 100°C since the DS18B20 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 DS18B20 be
powered by an external power supply.
In some situations the bus master may not know whether the DS18B20s on the bus are parasite powered
or powered by external supplies. The master needs this information to determine if the strong bus pullup
wwws.hdaotuaslhdeebt4eu.cuosmed 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 DS18B20s will pull the bus low, and externally
powered DS18B20s 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 DS18B20 DURING TEMPERATURE
CONVERSIONS Figure 4
VPU
Micro-
processor
VPU
4.7K
DS18B20
GND DQ VDD
1-Wire Bus
To Other
1-Wire Devices
POWERING THE DS18B20 WITH AN EXTERNAL SUPPLY Figure 5
Micro-
processor
VPU
4.7K
1-Wire Bus
DS18B20
GND DQ VDD
VDD (External Supply)
To Other
1-Wire Devices
64-BIT LASERED ROM CODE
Each DS18B20 contains a unique 64–bit code (see Figure 6) stored in ROM. The least significant 8 bits
of the ROM code contain the DS18B20’s 1–wire family code: 28h. 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 DS18B20 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 6
8-BIT CRC
48-BIT SERIAL NUMBER
8-BIT FAMILY CODE (28h)
MSB
LSB MSB
LSB MSB
LSB
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5 Page 
DS18B20
is issued the master must enable a strong pullup on the 1-wire bus for at least 10 ms as described in the
POWERING THE DS18B20 section.
RECALL E2 [B8h]
This command recalls the alarm trigger values (TH and TL) and configuration data from EEPROM and
places the data in bytes 2, 3, and 4, respectively, in the scratchpad memory. The master device can issue
read time slots following the Recall E2 command and the DS18B20 will indicate the status of the recall by
wwwt.rdaantassmheiettt4iun.gcom0 while the recall is in progress and 1 when the recall is done. The recall operation happens
automatically at power-up, so valid data is available in the scratchpad as soon as power is applied to the
device.
READ POWER SUPPLY [B4h]
The master device issues this command followed by a read time slot to determine if any DS18B20s on the
bus are using parasite power. During the read time slot, parasite powered DS18B20s will pull the bus
low, and externally powered DS18B20s will let the bus remain high. Refer to the POWERING THE
DS18B20 section for usage information for this command.
DS18B20 FUNCTION COMMAND SET Table 4
1-Wire Bus Activity
Command
Description
Protocol After Command is Issued
TEMPERATURE CONVERSION COMMANDS
Convert T
Initiates temperature
44h DS18B20 transmits conversion
conversion.
status to master (not applicable
for parasite-powered
DS18B20s).
MEMORY COMMANDS
Read Scratchpad Reads the entire scratchpad BEh DS18B20 transmits up to 9 data
including the CRC byte.
bytes to master.
Write Scratchpad Writes data into scratchpad
4Eh Master transmits 3 data bytes to
bytes 2, 3, and 4 (TH, TL,
and configuration registers).
DS18B20.
Copy Scratchpad Copies TH, TL, and
configuration register data
48h None
from the scratchpad to
Recall E2
EEPROM.
Recalls TH, TL, and
configuration register data
B8h DS18B20 transmits recall status
to master.
from EEPROM to the
scratchpad.
Read Power
Signals DS18B20 power
B4h DS18B20 transmits supply status
Supply
supply mode to the master.
to master.
Notes
1
2
3
1
NOTES:
1. For parasite-powered DS18B20s, the master must enable a strong pullup on the 1-wire bus during
temperature conversions and copies from the scratchpad to EEPROM. No other bus activity may take
place during this time.
2. The master can interrupt the transmission of data at any time by issuing a reset.
3. All three bytes must be written before a reset is issued.
11 of 20
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