SENSIRION SCD4 Series, Manual, Page: 19 / 24

www.sensirion.com Version 1.3 – September 2022 19/24
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 32 . 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 32 I
2
C CRC properties.