User Manual

ams Datasheet Page 21
[v1-06] 2019-Feb-07 Document Feedback
CCS811 − Application Register Overview
ENV_DATA (Environment Data) Register (0x05)
A multi-byte register that can be written with the current
Humidity and Temperature values if known.
Relative Humidity
Figure 19:
Relative Humidity Fields and Byte Order
Humidity is stored as an unsigned 16 bits in 1/512%RH. The
default value is 50% = 0x64, 0x00. As an example 48.5%
humidity would be 0x61, 0x00.
Temperature
Figure 20:
Temperature Fields and Byte Order
Temperature is stored as an unsigned 16 bits integer in 1/512
degrees; there is an offset: 0 maps to -25°C. The default value is
25°C = 0x64, 0x00. As an example 23.5% temperature would be
0x61, 0x00.
The internal algorithm uses ENV_DATA values (or default values
if not set by the application) to compensate for changes in
relative humidity and ambient temperature.
For temperatures below-25°C the 7-bit temperature field in
Byte 2 above should be set to all zeros.
Byte 0 Byte 1
Humidity High Byte Humidity Low Byte
7654321076543 2 1 0
64 32 1684211/21/41/81/161/321/641/1281/2561/512
Humidity % Humidity % Fraction
Byte 2 Byte 3
Temperature High Byte Temperature Low Byte
76543210 7 6 5 4 3 2 1 0
64 32 16 8 4 2 1 1/2 1/4 1/8 1/16 1/32 1/64 1/128 1/256 1/512
Temperature 25°C Temperature 25°C Fraction