m24lr16e-r STMicroelectronics, m24lr16e-r Datasheet - Page 139

• Manufacturer Part Number: m24lr16e-r
• Description: 16 Kbit Eeprom With Password Protection, Dual Interface & Energy Harvesting 400 Khz I²c Bus & Iso 15693 Rf Protocol At 13.56 Mhz
• Manufacturer: STMicroelectronics

M24LR16E
Appendix B
B.1
B.2
CRC error detection method
The cyclic redundancy check (CRC) is calculated on all data contained in a message, from
the start of the flags through to the end of Data. The CRC is used from VCD to M24LR16E-
R and from M24LR16E-R to VCD.
Table 131. CRC definition
To add extra protection against shifting errors, a further transformation on the calculated
CRC is made. The one’s complement of the calculated CRC is the value attached to the
message for transmission.
To check received messages, the two CRC bytes are often also included in the re-
calculation, for ease of use. In this case, the expected value for the generated CRC is the
residue F0B8h.
CRC calculation example
This example in C language illustrates one method of calculating the CRC on a given set of
bytes comprising a message.
C-example to calculate or check the CRC16 according to ISO/IEC 13239
#define
#define
#define
#define
#define
#define
void main()
{
4, 0x91, 0x39};
// calculate_or_check_crc = CHECK_CRC;// This could be an other
example
ISO/IEC 13239
unsigned char array_of_databytes[NUMBER_OF_BYTES + 2] = {1, 2, 3,
unsigned int
int
int
int
calculate_or_check_crc = CALC_CRC;
if (calculate_or_check_crc == CALC_CRC)
{
CRC type
POLYNOMIAL0x8408//
PRESET_VALUE0xFFFF
CHECK_VALUE0xF0B8
NUMBER_OF_BYTES4// Example: 4 data bytes
CALC_CRC1
CHECK_CRC0
CRC (informative)
Length
16 bits
current_crc_value;
number_of_databytes = NUMBER_OF_BYTES;
calculate_or_check_crc;
i, j;
X
Doc ID 018932 Rev 7
16
+ X
12
Polynomial
+ X
CRC definition
x^16 + x^12 + x^5 + 1
5
+ 1 = 8408h
Direction
Backward
Preset
FFFFh
CRC (informative)
Residue
F0B8h
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