SHT3X-DIS datasheet(8/18 Pages) ETC2

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Datasheet SHT3x-DIS

www.sensirion.com

October 2015 - Version 1

8/18

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 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 8).

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 9. 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 0 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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