www.sensirion.com / D1

Version 1

– December 2022

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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 10.

Measurement commands in single shot mode. The first “SCL free” block indicates a minimal waiting

time of 1 ms. (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 10).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.