SI7015-A20 Datasheet, PDF (18/39 Pages) Silicon Laboratories – DIGITAL IC HUMIDITY AND TEMPERATURE SENSOR

Si7015-A20
5. Host Interface
5.1. I²C Interface
The Si7015 has an I²C serial interface with a 7-bit address of 0x40. The Si7015 is a slave device supporting data
transfer rates up to 400 kHz. Table 20 shows the register summary of the Si7015.
5.1.1. Performing a Relative Humidity Measurement
The following steps should be performed in sequence to take a relative humidity measurement:
1. Set START (D0) in CONFIG to begin a new conversion.
2. Poll RDY (D0) in STATUS (register 0) until it is low (= 0). (This must be done at least once prior to reading
results even if the host waits longer than t_CONV.)
3. Read the upper and lower bytes of the RH value from DATAh and DATAl (registers 0x01 and 0x02),
respectively. Table 11 shows the format of the 12-bit relative humidity result.
4. Convert the RH value to %RH using the following equation:
%RH
=


R_{--1---6H---}
– 24
where RH is the measured value returned in DATAh:DATAI.
5. Apply temperature compensation as discussed elsewhere in this data sheet.
Due to normal variations in RH accuracy of the device as described in Table 4, it is possible for the measured value
of %RH to be slightly less than 0 when the actual RH level is close to or equal to 0. Similarly, the measured value
of %RH may be slightly greater than 100 when the actual RH level is close to or equal to 100. This is expected
behavior, and it is acceptable to limit the range of RH results to 0 to 100%RH in the host software by truncating
values that are slightly outside of this range.
Table 12 shows the 12-bit values that correspond to various measured RH levels.
Table 11. 12-Bit Relative Humidity Result Available in Registers 1 and 2
DATAh
DATAI
D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
12-Bit Relative Humidity Code
18
Rev. 1.0