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SI7005-B-FM

DIGITAL I2C HUMIDITY AND TEMPERATURE SENSOR

Silicon Laboratories 

Si7005

5. Host Interface

5.1. I2C Interface

The Si7005 has an I2C serial interface with a 7-bit address of 0x40. The Si7005 is a slave device supporting data

transfer rates up to 400 kHz. Table 24 shows the register summary of the Si7005.

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)

3. Read the upper and lower bytes of the RH value from DATAh and DATAl (registers 0x01 and 0x02),

respectively. Table 14 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 and/or linearization as discussed elsewhere in this data sheet

Table 15 shows the 12-bit values that correspond to various measured RH levels.

Table 14. 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

0

0

0

0

Table 15. Typical %RH Measurement Codes for 0 to 100% RH Range

%RH

0

10

20

30

40

50

60

70

80

90

100

12 Bit Code

Dec

Hex

384

180

544

220

704

2C0

864

360

1024

400

1184

4A0

1344

540

1504

5E0

1664

680

1824

720

1984

7C0

The above sequence assumes normal mode, i.e., tCONV = 35 ms (typical). Conversions may be performed in fast

mode. See section “5.1.3. Fast Conversion Mode”.

Rev. 1.3

19

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