www.sensirion.com / D1

Version 2

– July 2021

10/17

4.4 Command Overview

Command

(hex)

Response length

incl. CRC (bytes)

Description

[return values]

0xFD

6

measure T & RH with high precision (high repeatability)

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

0xF6

6

measure T & RH with medium precision (medium repeatability)

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

0xE0

6

measure T & RH with lowest precision (low repeatability)

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

0x89

6

read serial number

[2 * 8-bit data; 8-bit CRC; 2 * 8-bit data; 8-bit CRC]

0x94

-

soft reset

[ACK]

0x39

6

activate heater with 200mW for 1s, including a high precision

measurement just before deactivation

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

0x32

6

activate heater with 200mW for 0.1s including a high precision

measurement just before deactivation

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

0x2F

6

activate heater with 110mW for 1s including a high precision

measurement just before deactivation

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

0x24

6

activate heater with 110mW for 0.1s including a high precision

measurement just before deactivation

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

0x1E

6

activate heater with 20mW for 1s including a high precision

measurement just before deactivation

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

0x15

6

activate heater with 20mW for 0.1s including a high precision

measurement just before deactivation

[2 * 8-bit T-data; 8-bit CRC; 2 * 8-bit RH-data; 8-bit CRC]

Table 7 Overview of I2C commands. If the sensor is not ready to process a command, e.g. because it is still

measuring, it will response with NACK to the I2C read header. Given heater power values are typical and

valid for VDD=3.3V.

4.5 Conversion of Signal Output

The digital sensor signals correspond to following humidity and temperature values:

������������ = (−6 + 125 ∙

������������������

216 − 1

) %RH

( 1 )

������ = (−45 + 175 ∙

������������

216 − 1

) °C

( 2 )

������ = (−49 + 315 ∙

������������

216 − 1

) °F

( 3 )

N.B.: The RH conversion formula (1) allows values to be reported which are outside of the range

of 0

%RH … 100 %RH. Relative humidity values which are smaller than 0 %RH and larger than

100 %RH are non-physical, how

ever these “uncropped” values might be found beneficial in some

cases (e.g. when the distribution of the sensors at the measurement boundaries are of interest).

For all users who do not want to engage in evaluation of these non-physical values, cropping of

the RH signal to the range of 0

%RH … 100 %RH is advised.