SI7005EVB-UDP データシートの表示（PDF） - Silicon Laboratories

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SI7005EVB-UDP

DIGITAL I2C HUMIDITY AND TEMPERATURE SENSOR

Silicon Laboratories 

Si7005

5.2. I2C Operation

The Si7005 uses a digital I2C interface. If the Si7005 shares an I2C bus with other slave devices, it should be

powered down when the master controller is communicating with the other slave devices. The Si7005 can be

powered down either by setting the CS signal to logic high or setting the VDD pin to 0 V. A method of achieving this

by powering the Si7005 from an MCU GPIO is shown in Figure 5.

The format of the address byte is shown in Table 20.

Table 20. I2C Slave Address Byte

A6

A5

A4

A3

A2

A1

A0

R/W

1

0

0

0

0

0

0

1/0

5.2.1. I2C Write Operation

To write to a register on the Si7005, the master should issue a start command (S) followed by the slave address,

0x40. The slave address is followed by a 0 to indicate that the operation is a write. Upon recognizing its slave

address, the Si7005 issues an acknowledge (A) by pulling the SDA line low for the high duration of the ninth SCL

cycle. The next byte the master places on the bus is the register address pointer, selecting the register on the

Si7005 to which the data should be transferred. After the Si7005 acknowledges this byte, the master places a data

byte on the bus. This byte will be written to the register selected by the address pointer. The Si7005 will

acknowledge the data byte, after which the master issues a Stop command (P). See Table 21.

Master Slave

Table 21. I2C Write Sequence

Sequence to Write to a Register

S Slave Address W A Address Pointer A Register Data A P

Sequence to Start a Relative Humidity Conversion

S

0x40

0A

0x03

A

0x01

AP

Sequence to Start a Temperature Conversion

S

0x40

0A

0x03

A

0x11

AP

Rev. 1.3

23

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