HTU20P 查看數據表（PDF） - Unspecified

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HTU20P

Digital Relative Humidity sensor with Temperature output

Unspecified 

HTU21D(F) Sensor

Digital Relative Humidity sensor with Temperature output

Command

Trigger Temperature Measurement

Trigger Humidity Measurement

Trigger Temperature Measurement

Trigger Humidity Measurement

Write user register

Read user register

Soft Reset

Code

0xE3

0xE5

0xF3

0xF5

0xE6

0xE7

0xFE

Comment

Hold master

Hold master

No Hold master

No Hold master

 Hold/No Hold master modes

There are two different operation modes to communicate with the HTU21D(F) sensor: Hold Master mode and

No Hold Master mode.

In the first case, the SCK line is blocked (controlled by HTU21D(F) sensor) during measurement process while

in the second case the SCK line remain open for other communication while the sensor is processing the

measurement.

No Hold Master mode allows for processing other I²C communication tasks on a bus while the HTU21D(F)

sensor is measuring. A communication sequence of the two modes is available below.

In the Hold Master mode, the HTU21D(F) pulls down the SCK line while measuring to force the master into a

wait state. By releasing the SCK line, the HTU21D(F) sensor indicates that internal processing is completed and

that transmission may be continued.

In the No Hold Master mode, the MCU has to poll for the termination of the internal processing of the

HTU21D(F) sensor. This is done by sending a start condition followed by the I²C header (‘1’ for Read access:

0x81) as shown below. If the internal processing is finished, the HTU21D(F) sensor acknowledges the poll of the

MCU and data can be read by the MCU. If the measurement processing is not finished, the HTU21D(F) sensor

answers no ACK bit and start condition must be issued once more.

For both modes, since the maximum resolution of the measurement is 14 bits, the two last least significant bits

(LSBs, bits 43 and 44) are used for transmitting status information. Bit 1 of the two LSBs indicates the

measurement type (‘0’: temperature, ‘1’: humidity). Bit 0 is currently not assigned.

12345678

9 10 11 12 13 14 15 16 17 18

S 1 0 0 0 0 0 0 0 ACK 1 1 1 0 0 1 0 1 ACK

I²C address + write

Command (see table p.9)

19 20 21 22 23 24 25 26 27

S 1 0 0 0 0 0 0 1 ACK

Measurement

I²C address + read

Hold during measurement

28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

0 1 1 1 1 1 0 0 ACK 1 0 0 0 0 0 1 0 ACK

Data (MSB)

Data (LSB)

Status

46 47 48 49 50 51 52 53 54

1 0 0 1 0 1 1 1 NACK P

Checksum

Hold Master communication sequence

HPC199_3 HTU21D(F) Sensor Datasheet

www.meas-spec.com

11/21

October 2013

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