SI7021-A20 Datasheet, PDF (23/36 Pages) Silicon Laboratories – IC HUMIDITY AND TEMPERATURE SENSOR

Si7021-A20
5.2. Reading and Writing User Registers
There is one user register on the Si7021 that allows the user to set the configuration of the Si7021. The procedure
for accessing that register is described below.
The checksum byte is not supported after reading a user register.
Sequence to read a register
Slave
Read Reg
S
W
A
A
Address
Cmd
Slave
Sr
R
Address
A
Read Data NA P
Sequence to write a register
S
Slave Address
W
A
Write Reg Cmd
A
Write Data
A
P
5.3. Electronic Serial Number
The Si7021 provides a serial number individualized for each device that can be read via the I²C serial interface.
Two I²C commands are required to access the device memory and retrieve the complete serial number. The
command sequence, and format of the serial number response is described in the figure below:
First access:
Master
Slave
S
S
2nd access:
S
S
Slave Address W
Slave Address R
SNA_3
ACK
SNA_1
ACK
Slave Address W
Slave Address R
SNB_3
ACK
SNB_1
ACK
ACK
ACK
CRC
CRC
ACK
ACK
SNB_2
SNB_0
0xFA
ACK
ACK
0xFC
ACK
ACK
ACK 0X0F
SNA_2 ACK
SNA_0 ACK
ACK 0XC9
CRC
ACK
CRC NACK
ACK
CRC ACK
CRC NACK P
ACK
P
Rev. 1.1
23