SHT35 datasheet(13/20 Pages) ETC2

13 / 20 page

Datasheet SHT3x-DIS

www.sensirion.com

August 2016 - Version 3

13/20

Command

Hex code

Read Out of status register

0xF32D

Table 16 Command to read out the status register (Clear

blocks are controlled by the microcontroller, grey blocks by

the sensor).

Bit Field description

Default

value

Alert pending status

'0': no pending alerts

'1': at least one pending alert

‘1’

Reserved

‘0’

Heater status

‘0’ : Heater OFF

‘1’ : Heater ON

‘0’

Reserved

‘0’

RH tracking alert

‘0’ : no alert

‘1’ . alert

‘0

T tracking alert

‘0’ : no alert

‘1’ . alert

‘0’

9:5 Reserved

‘xxxxx’

System reset detected

'0': no reset detected since last ‘clear

status register’ command

'1': reset detected (hard reset, soft reset

command or supply fail)

‘1’

3:2

Reserved

‘00’

Command status

'0': last command executed successfully

'1': last command not processed. It was

either invalid, failed the integrated

command checksum

‘0’

Write data checksum status

'0': checksum of last write transfer was

correct

'1': checksum of last write transfer failed

‘0’

Table 17 Description of the status register.

Clear Status Register

All flags (Bit 15, 11, 10, 4) in the status register can be

cleared (set to zero) by sending the command shown in

Table 18.

Command

Hex Code

Clear status register

0x 30 41

Table 18 Command to clear the status register (Clear

blocks are controlled by the microcontroller, grey blocks by

the sensor).

4.12 Checksum Calculation

The 8-bit CRC checksum transmitted after each data

word is generated by a CRC algorithm.Its properties are

displayed in Table 19. The CRC covers the contents of

the two previously transmitted data bytes. To calculate

the checksum onlythese two previouslytransmitted data

bytes are used.

Property

Value

Name

CRC-8

Width

8 bit

Protected data

read and/or write data

Polynomial

0x31 (x8 + x5 + x4 + 1)

Initialization

0xFF

Reflect input

False

Reflect output

False

Final XOR

0x00

Examples

CRC (0xBEEF) = 0x92

Table 19 I2C CRC properties.

4.13 Conversion of Signal Output

Measurementdata is always transferred as 16-bitvalues

(unsigned integer). These values are already linearized

and compensated for temperature and supply voltage

effects. Converting those raw values into a physical

scale can be achieved using the following formulas.

Relative humidityconversion formula (resultin %RH):







100

Temperature conversion formula (resultin °C & °F):

 

























315

175

SRH and ST denote the raw sensor output for humidity

and temperature, respectively. The formulas work only

correctly when SRH and ST are used in decimal

representation.

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