SCD40-D-R2 datasheet(7/22 Pages) SENSIRION

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3 Digital Interface Description

All SCD4x commands and data are mapped to a 16-bit address space.

SCD4x

Hex. Code

I2C address

0x62

Table 8 I2C device address.

3.1 Power-Up and Communication Start

The sensor starts powering-up after reaching the power-up threshold voltage VDD,Min = 2.25 V. After reaching this threshold

voltage, the sensor needs 1000 ms to enter the idle state. Once the idle state is entered it is ready to receive commands from

the master.

Each transmission sequence begins with a START condition (S) and ends with a STOP condition (P) as described in the I2C-

bus specification.

3.2 Data type & length

Data sent to and received from the sensor consists of a sequence of 16-bit commands and/or 16-bit words (each to be interpreted

as unsigned integer, most significant byte transmitted first). Each data word is immediately succeeded by an 8-bit CRC. In write

direction it is mandatory to transmit the checksum. In read direction it is up to the master to decide if it wants to process the

checksum (see chapter 3.11).

3.3 Command Sequence Types

The SCD4x features four different I2C command sequence types: “read I2C sequences”, “write I2C sequences”,“send I2C

command” and “send command and fetch result” sequences. Figure 2 illustrates how the I2C communication for the different

sequence types is built-up.

Figure 2: Command Sequence types: “write” sequence, “send command” sequence, “read”

sequence, and “send command and fetch result” sequence.

For “read”” or “send command and fetch results” sequences, after writing the address and/or data to the sensor and sending the

ACK bit, the sensor needs the execution time (see Table 9) to respond to the I2C read header with an ACK bit. Hence, it is

required to wait the command execution time before issuing the read header. Commands must not be sent while a previous

command is being processed.

SCD40-D-R2 数据表(PDF) 7 Page - Sensirion AG Switzerland