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Version 1.1 – April 2021

15/22

3.9 Advanced Features

3.9.1

persist_settings

Description: Configuration settings such as the temperature offset, sensor altitude and the ASC enabled/disabled parameter

are by default stored in the volatile memory (RAM) only and will be lost after a power-cycle. The persist_settings command

stores the current configuration in the EEPROM of the SCD4x, making them persistent across power-cycling. To avoid

unnecessary wear of the EEPROM, the persist_settings command should only be sent when persistence is required and if actual

changes to the configuration have been made. The EEPROM is guaranteed to endure at least 2000 write cycles before failure.

Note that field calibration history (i.e. FRC and ASC, see chapter 3.7) is automatically stored in a separate EEPROM

dimensioned for the specified sensor lifetime.

Write

(hexadecimal)

Input parameter: -

Response parameter: -

Max. command

duration [ms]

length [bytes]

signal conversion

length [bytes]

signal conversion

0x3615

-

-

-

-

800

Example: persist settings

Write

0x3615

(hexadecimal)

Command

3.9.2

get_serial_number

Description: Reading out the serial number can be used to identify the chip and to verify the presence of the sensor.

The get serial number command returns 3 words, and every word is followed by an 8-bit CRC checksum. Together, the 3 words

constitute a unique serial number with a length of 48 bits (big endian format).

Write

(hexadecimal)

Input parameter: -

Response parameter: serial number

Max. command

duration [ms]

length [bytes]

signal conversion

length [bytes]

signal conversion

0x3682

-

-

9

Serial number = word[0] <<

32 | word[1] << 16 | word[2]

1

Example: serial number is 273’325’796’834’238

Write

0x3682

(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0xf896

0x31

0x9f07

0xc2

0x3bbe

0x89

(hexadecimal)

word[0]

CRC of 0xf896

word[1]

CRC of 0x9f07

word[2]

CRC of 0x3bbe