SI7020-A20 Datasheet, PDF (24/36 Pages) Silicon Laboratories – IC HUMIDITY AND TEMPERATURE SENSOR

Si7020-A20
5.2. Reading and Writing User Registers
There is one user register on the Si7020 that allows the user to set the configuration of the Si7020. 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 Si7020 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 Slave Address W
ACK
0xFA
ACK
0X0F
S Slave Address R
ACK
SNA_3
ACK CRC
ACK SNA_2 ACK
2nd access:
SNA_1
ACK CRC
ACK SNA_0 ACK
S Slave Address W
ACK
0xFC
ACK
0XC9
S Slave Address R
ACK
SNB_3
ACK SNB_2 ACK
CRC
ACK
SNB_1
ACK SNB_0 ACK
CRC NACK
ACK
CRC ACK
CRC NACK P
ACK
P
The format of the complete serial number is 64-bits in length, divided into 8 data bytes. The complete serial number
sequence is shown below:
SNA_3
SNA_2
SNA_1
SNA_0
SNB_3
SNB_2
SNB_1
SNB_0
The SNB3 field contains the device identification to distinguish between the different Silicon Labs relative humidity
and temperature devices. The value of this field maps to the following devices according to this table:
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Rev. 1.1