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Version 3.3 – November 2024

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After the reset command the sensor is in the same state as after a power-up cycle. Reset takes a maximum of

12ms. During this time the sensor will not acknowledge its address nor accept commands.

3.3.12 Sensor state retention

The sensor stores settings like the gas model or reference values of FRC and ASC in volatile memory. These are

not retained when the sensor loses power and must be stored externally to be sent to the sensor after each

power cycle.

To store the state of the sensor externally use the following two commands

1. Prepare read state

2. Read state

Check the CRC of the state and store the 30 bytes. After each power cycle return the state to the sensor by

using the two commands

1. Write state

2. Apply state

The sensor state contains the following information:

•

Selected binary gas index (see 3.3.2)

•

ON or OFF flag and offset value to apply to the sensor’s output for the ASC (automatic self-calibration,

see 3.3.8)

•

Offset value to apply to the sensor’s output used in FRC and ASC (forced recalibration, see 3.3.7)

•

Compensation inputs: last supplied values of temperature (see 3.3.4), humidity (see 3.3.3) and pressure

(see 3.3.5)

Remark on what is not part of the sensor state:

•

If CRC disabling is desired, it needs to be disabled after each wake-up

•

The noise filter (see section 3.3.9) is not saved in the sensor state and therefore, this filtering cannot

be used in combination with sleep mode.

Command

Command code

(hex)

Consecutive read

Description

Prepare read state

0x3752

NA

The sensor will prepare its current state

to be read out. Please wait 2 ms before

sending the next command.

Read state

0xE133

30 bytes (10 times

16-bit word + CRC)

Read out the sensor state. The 30 bytes

must be stored on the microcontroller

to be written back to the sensor after

exiting sleep mode

Command

Command code

(hex)

Argument

Description

Write state

0xE133

30 bytes (10 times

16-bit word + CRC)

Write the sensor state as read out

earlier with the “Read state” (0xE133)

command.

Apply state

0x3650

NA

The sensor will apply the written state

data. Please wait 2 ms before sending

the next command.

It is important to check that no corrupted state is applied to the sensor. Therefore, abort the process as soon

as a NACK is received during the Read state or Write state commands. Example procedures of sensor state

retention can be found in the Design Guide.