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ds18b20资料有英文有中文
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ds18b20资料有英文有中文~~~~~~~~~~~~~~~~~~~··
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中英文资料
DS18B20
Programmable Resolution
1-Wire Digital Thermometer
FEATURES
_Unique 1-WireTM interface requires only oneport
pin for communication
_.Multidrop capability simplifies distributedtemperature
sensing applications
_ Requires no external components
_ Can be powered from data line. Power supply
range is 3.0V to 5.5V
_ Zero standby power required
_ Measures temperatures from -55°C to
+125°C. Fahrenheit equivalent is -67°F to
+257°F
_ 0.5C accuracy from -10°C to +85°C
_ Thermometer resolution is programmable
from 9 to 12 bits
_ Converts 12-bit temperature to digital word in
750 ms (max.)
_ User-definable, nonvolatile temperature alarm
settings
_ Alarm search command identifies and
addresses devices whose temperature is
outside of programmed limits (temperature
alarm condition)
_ Applications include thermostatic controls,
industrial systems, consumer products,
thermometers, or any thermally sensitive
system
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 (configurable) temperature readings
which
indicate the temperature of the device.
Information is sent to/from the DS18B20 over a 1-Wire interface, so that only one wire (and
ground)
needs to be connected from a central microprocessor to a DS18B20. Power for reading,
writing, and
performing temperature conversions can be derived from the data line itself with no need for an
external
power source.
Because each DS18B20 contains a unique silicon serial number, multiple DS18B20s can exist
on the
same 1-Wire bus. This allows for placing temperature sensors in many different places.
Applications
where this feature is useful include HVAC environmental controls, sensing temperatures inside
buildings,
equipment or machinery, and process monitoring and control.
DETAILED PIN DESCRIPTION Table 1
DS18B20Z (8-pin SOIC) and DS18P20P (TSOC): All pins not specified in this table are not to
be
connected.
OVERVIEW
The block diagram of Figure 1 shows the major components of the DS18B20. The DS18B20
has four
main data components: 1) 64-bit lasered ROM, 2) temperature sensor, 3) nonvolatile
temperature alarm
triggers TH and TL, and 4) a configuration register. The device derives its power from the 1-
Wire
communication line by storing energy on an internal capacitor during periods of time when the
signal line
is high and continues to operate off this power source during the low times of the 1-Wire line
until it
returns high to replenish the parasite (capacitor) supply. As an alternative, the DS18B20 may
also be
powered from an external 3V - 5.5V supply.
Communication to the DS18B20 is via a 1-Wire port. With the 1-Wire port, the memory and
control
functions will not be available before the ROM function protocol has been established. The
master must
first provide one of five ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search
ROM, 4)
Skip ROM, or 5) Alarm Search. These commands operate on the 64-bit lasered ROM portion
of each
device and can single out a specific device if many are present on the 1-Wire line as well as
indicate to
the bus master how many and what types of devices are present. After a ROM function
sequence has been
successfully executed, the memory and control functions are accessible and the master may
then provide
any one of the six memory and control function commands.
One control function command instructs the DS18B20 to perform a temperature measurement.
The result
of this measurement will be placed in the DS18B20’s scratch-pad memory, and may be read by
issuing a
memory function command which reads the contents of the scratchpad memory. The
temperature alarm
triggers TH and TL consist of 1 byte EEPROM each. If the alarm search command is not
applied to the
DS18B20, these registers may be used as general purpose user memory. The scratchpad also
contains a
configuration byte to set the desired resolution of the temperature to digital conversion. Writing
TH, TL,
and the configuration byte is done using a memory function command. Read access to these
registers is
through the scratchpad. All data is read and written least significant bit first.
DS18B20
3 of 26
DS18B20 BLOCK DIAGRAM Figure 1
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals”
power
whenever the DQ or VDD pins are high. DQ will provide sufficient power as long as the
specified timing
and voltage requirements are met (see the section titled “1-Wire Bus System”). The advantages
of
parasite power are twofold: 1) by parasiting off this pin, no local power source is needed for
remote
sensing of temperature, and 2) the ROM may be read in absence of normal power.
In order for the DS18B20 to be able to perform accurate temperature conversions, sufficient
power must
be provided over the DQ line when a temperature conversion is taking place. Since the
operating current
of the DS18B20 is up to 1.5 mA, the DQ line will not have sufficient drive due to the 5k pullup
resistor.
This problem is particularly acute if several DS18B20s are on the same DQ and attempting to
convert
simultaneously.
There are two ways to assure that the DS18B20 has sufficient supply current during its active
conversion
cycle. The first is to provide a strong pullup on the DQ line whenever temperature conversions
or copies
to the E2
memory are taking place. This may be accomplished by using a MOSFET to pull the DQ line
directly to the power supply as shown in Figure 2. The DQ line must be switched over to the
strong pullup
within 10 s maximum after issuing any protocol that involves copying to the E2 memory or
initiates
temperature conversions.
This allows other data traffic on the 1-Wire bus during the conversion time. In addition, any
number of
DS18B20s may be placed on the 1-Wire bus, and if they all use external power, they may all
simultaneously perform temperature conversions by issuing the Skip ROM command and then
issuing the
Convert T command. Note that as long as the external power supply is active, the GND pin
may not be
floating.
The use of parasite power is not recommended above 100C, since it may not be able to sustain
communications given the higher leakage currents the DS18B20 exhibits at these temperatures.
For
applications in which such temperatures are likely, it is strongly recommended that VDD be
applied to the
DS18B20.
For situations where the bus master does not know whether the DS18B20s on the bus are
parasite
powered or supplied with external VDD, a provision is made in the DS18B20 to signal the
power supply
scheme used. The bus master can determine if any DS18B20s are on the bus which require the
strong
pullup by sending a Skip ROM protocol, then issuing the read power supply command. After
this
command is issued, the master then issues read time slots. The DS18B20 will send back “0” on
the 1-
Wire bus if it is parasite powered; it will send back a “1” if it is powered from the VDD pin. If
the master
receives a “0,” it knows that it must supply the strong pullup on the DQ line during
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