www.sensirion.com
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.
Table 23
: persist_settings I
2
C sequence description
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).
Table 24
: get_serial_number I
2
C sequence description
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
