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USING THE SENSOR
This temperature sensor provides a digital output signal to
allow easy interfacing to a microcontroller or a micropro-
cessor using the 1-Wire® communication protocol. Since
communication with the sensor is digital, it can be placed
at a distance from the controller circuit without worrying
about disturbances and interference from the surrounding
environment.
The thermal sensor board uses three connections: Vcc
(5V power), GND and a bidirectional data line (DQ). The
DS18B20's temperature measurements range between
-55°C and +125° C and are expressed in 9 to 12 bit reso-
lution (user definable) with ±0.5°C accuracy in the -10°C
to 85°C range. Resolution is set through the configuration
register.
Red wire
Black wire
5V positive
GND negative
power supply
power supply
The DS18B20 is capable of expressing temperatures with decimal values. Looking at Fig. 1, you will see that the
first four least significant bit values are less than 1. The first one 0.0625, the second one is 0.125, that the third
one is 0.25 and that the fourth one is 0.5.
Fig. The structure of the two bits successively emitted by the MM101, each time it is queried: the LS byte is
the one weighing less, while the MSB byte is the more significate one. This structure is referred to as an 11-bit
representation, plus sign.
USER MANUAL
MM101
Yellow wire
Temperature output/
data request
To begin temperature measurement and A/D
conversion the "Convert T" (code: 44h) command
is issued. The sensor transmits a 0 during the
conversion and returns a 1 when the operation is
complete. The resulting two bytes are available
in the sensor's scratchpad memory and corre-
spond to the measured temperature, expressed
in Celsius. The "Read ScratchPad" (code: BEh)
command is used to access the measurement
from memory. The 2-byte register (for an 11-bit
sampling) is structured as shown in Fig. 1. The
structure of the 2 bytes returned in 11-bit mode
are as follows: the first 11 bits (including all of the
least significate byte and the first three bits from
the most significate byte) express the temperature
value, the last five express the sign and are all 0's
if the temperate is positive (above zero) and all 1's
if the temperature is negative (below zero).
2
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