SCD40-D-R2 datasheet(18/22 Pages) SENSIRION

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3.11 Checksum Calculation

The 8-bit CRC checksum transmitted after each data word is generated by a CRC algorithm. Its properties are displayed in

Table 30. The CRC covers the contents of the two previously transmitted data bytes. To calculate the checksum only these two

previously transmitted data bytes are used. Note that command words are not followed by CRC.

Property

Value

Example code (C/C++)

Name

CRC-8

#define CRC8_POLYNOMIAL 0x31

#define CRC8_INIT 0xFF

uint8_t sensirion_common_generate_crc(const uint8_t* data, uint16_t count) {

uint16_t current_byte;

uint8_t crc = CRC8_INIT;

uint8_t crc_bit;

/* calculates 8-Bit checksum with given polynomial */

for (current_byte = 0; current_byte < count; ++current_byte) {

crc ^= (data[current_byte]);

for (crc_bit = 8; crc_bit > 0; --crc_bit) {

if (crc & 0x80)

crc = (crc << 1) ^ CRC8_POLYNOMIAL;

else

crc = (crc << 1);

}

return crc;

}

Width

8 bit

Protected Data

read and/or write data

Polynomial

0x31 (x8 + x5 + x4 + 1)

Initialization

0xFF

Reflect input

False

Reflect output

False

Final XOR

0x00

Examples

CRC (0xBEEF) = 0x92

Table 30 I2C CRC properties.

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