Data Sheet

Datasheet SHT3x-DIS
www.sensirion.com May 2018- Version 5 10/22
In single shot mode different measurement commands
can be selected. The 16 bit commands are shown in
Table 9. They differ with respect to repeatability (low,
medium and high) and clock stretching (enabled or
disabled).
The repeatability setting influences the measurement
duration and thus the overall energy consumption of the
sensor. This is explained in section 2.
Condition
Hex. code
Repeatability
Clock
stretching
MSB
LSB
High
enabled
0x2C
06
Medium
0D
Low
10
High
disabled
0x24
00
Medium
0B
Low
16
e.g. 0x2C06: high repeatability measurement with clock
stretching enabled
Table 9 Measurement commands in single shot mode. The
first “SCL free” block indicates a minimal waiting time of 1ms.
(Clear blocks are controlled by the microcontroller, grey
blocks by the sensor).
4.4 Readout of Measurement Results for
Single Shot Mode
After the sensor has completed the measurement, the
master can read the measurement results (pair of RH&
T) by sending a START condition followed by an I2C
read header. The sensor will acknowledge the reception
of the read header and send two bytes of data
(temperature) followed by one byte CRC checksum and
another two bytes of data (relative humidity) followed by
one byte CRC checksum. Each byte must be
acknowledged by the microcontroller with an ACK
condition for the sensor to continue sending data. If the
sensor does not receive an ACK from the master after
any byte of data, it will not continue sending data.
The sensor will send the temperature value first and then
the relative humidity value. After having received the
checksum for the humidity value a NACK and stop
condition should be sent (see Table 9).
The I2C master can abort the read transfer with a NACK
condition after any data byte if it is not interested in
subsequent data, e.g. the CRC byte or the second
measurement result, in order to save time.
In case the user needs humidity and temperature data
but does not want to process CRC data, it is
recommended to read the two temperature bytes of data
with the CRC byte (without processing the CRC data);
after having read the two humidity bytes, the read
transfer can be aborted with a with a NACK.
No Clock Stretching
When a command without clock stretching has been
issued, the sensor responds to a read header with a not
acknowledge (NACK), if no data is present.
Clock Stretching
When a command with clock stretching has been issued,
the sensor responds to a read header with an ACK and
subsequently pulls down the SCL line. The SCL line is
pulled down until the measurement is complete. As soon
as the measurement is complete, the sensor releases
the SCL line and sends the measurement results.
4.5 Measurement Commands for Periodic
Data Acquisition Mode
In this mode one issued measurement command yields
a stream of data pairs. Each data pair consists of one 16
bit temperature and one 16 bit humidity value (in this
order).
In periodic mode different measurement commands can
be selected. The corresponding 16 bit commands are
shown in Table 10. They differ with respect to
repeatability (low, medium and high) and data
acquisition frequency (0.5, 1, 2, 4 & 10 measurements
per second, mps). Clock stretching cannot be selected in
this mode.
The data acquisition frequency and the repeatability
setting influences the measurement duration and the
current consumption of the sensor. This is explained in
section 2 of this datasheet.
If a measurement command is issued, while the sensor
is busy with a measurement (measurement durations
see Table 4), it is recommended to issue a break
command first (see section 4.8). Upon reception of the