SHT35 datasheet(10/20 Pages) ETC2

10 / 20 page

Datasheet SHT3x-DIS

www.sensirion.com

August 2016 - Version 3

10/20

Condition

Hex. code

Repeatability

Clock

stretching

MSB

LSB

High

enabled

0x2C

Medium

Low

High

disabled

0x24

Medium

Low

e.g. 0x2C06: high repeatability measurement with clock

stretching enabled

Table 8 Measurement commands in single shot mode (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 firstand then

the relative humidity value. After having received the

checksum for the humidity value a NACK and stop

condition should be sent(see Table 8).

The I2C master can abortthe 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

measurementresult,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 commandwith clock stretchinghas 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 measurementis complete.As soon

as the measurement is complete, the sensor releases

the SCL line and sends the measurementresults.

4.5

Measurement Commands for Periodic

Data Acquisition Mode

In this mode one issued measurementcommand yields

a stream of data pairs. Each data pair consists ofone 16

bit temperature and one 16 bit humidity value (in this

order).

In periodic mode differentmeasurementcommands can

be selected. The corresponding 16 bit commands are

shown in Table 9.Theydiffer with respectto repeatability

(low, medium and high) and data acquisition frequency

(0.5, 1,2, 4 & 10 measurements per second,mps).Clock

stretching cannotbe 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

break command the sensor will finish the ongoing

measurement and enter the single shot mode.

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