SHTW2 datasheet(7/14 Pages) ETC2

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Version 2 – August 2016

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be sent to SHTW2 according to Figure 8. This triggers the

sensor to reset all internal state machines and reload

calibration data from the memory.

Command

Hex. Code

Bin. Code

Software reset

0x805D

1000’0000’0101’1101

Table 10 Soft reset command.

5.7 Read-out of ID Register

The SHTW2 has an ID register which contains an SHTW2-

specific product code. The read-out of the ID register can

be used to verify the presence of the sensor and proper

communication. The command to read the ID register is

shown in Table 11.

Command

Hex. Code

Bin. Code

Read ID register

0xEFC8

1110’1111’1100’1000

Table 11 Read-out command of ID register.

It needs to be sent to the SHTW2 after an I2C write

header. After the SHTW2 has acknowledged the proper

reception of the command, the master can send an I2C

read header and the SHTW2 will submit the 16-bit ID

followed by 8 bits of CRC. The structure of the ID is

described in Table 12.

16-bit ID

xxxx'xxxx’xx 00’0111

bits 5 to 0: SHTW2-specific product code

bits 15 to 6: unspecified information

Table 12 Structure of the 16-bit ID. Bits 15:6 of the ID contain

unspecified information (marked as “x”), which may vary from

sensor to sensor, while bits 5:0 contain the SHTW2-specific

product code.

5.8 Checksum Calculation

The 8-bit CRC checksum transmitted after each data word

is generated by a CRC algorithm with the properties

displayed in Table 13. The CRC covers the contents of the

two previously transmitted data bytes.

Property

Value

Name

CRC-8

Width

8 bits

Polynomial

0x31 (x8 + x5 + x4 + 1)

Initialization

0xFF

Reflect input

False

Reflect output

False

Final XOR

0x00

Examples

CRC (0x00) = 0xAC

CRC (0xBEEF) = 0x92

Table 13 SHTW2

I2C CRC properties.

5.9 Conversion of Signal Output

Measurement data is always transferred as 16-bit values.

These values are already linearized and temperature

compensated by the SHTW2. Humidity and temperature

values can be calculated with the formulas in given below.

Relative humidity conversion formula (result in %RH):

100





Temperature conversion formula (result in °C):

175









SRH and ST denote the raw sensor output (as decimal

values) for humidity and temperature, respectively.

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