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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 11. 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

influence 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 5), it is recommended to issue a break

command first (see section 4.8). Upon reception of the break command the sensor abort the

ongoing measurement and enter the single shot mode.

Condition

Hex. code

Repeatability

mps

MSB

LSB

High

0.5

0x20

32

Medium

24

Low

2F

High

1

0x21

30

Medium

26

Low

2D

High

2

0x22

36

Medium

20

Low

2B

High

4

0x23

34

Medium

22

Low

29

High

10

0x27

37

Medium

21

Low

2A

e.g. 0x2130: 1 high repeatability mps - measurement per second

Table 11. Measurement commands for periodic data acquisition mode (Clear blocks are controlled by the

microcontroller, grey blocks by the sensor). N.B.: At the highest mps setting self-heating of the sensor might

occur.

4.6 Readout of Measurement Results for Periodic Mode

Transmission of the measurement data can be initiated through the fetch data command shown in

Table 12. If no measurement data is present the I2C read header is responded with a NACK (Bit

9 in Table 12) and the communication stops. After the read-out command fetch data has been

issued, the data memory is cleared, i.e. no measurement data is present.

S

W

I2C Address

1

2

3

4

5

6

7

8

9

Command MSB

1

2

3

4

5

6

7

8

9

Command LSB

10 11 12 13 14 15 16 17 18

16-bit command

I2C write header