Posted on January 04, 2017 at 15:39Hi everyone,
in our application I have to communicate with a M24SR02-Y over IIC.
I have tried 2 versions to generate the CRC:
Version 2
#define PRESET_VALUE 0x6363
#define MASK 0x8408
#define NUMBER_OF_BYTES 6
unsigned char array_of_databytes[6] = { 0x03, 0x00, 0xB0, 0x00, 0x00, 0x02 };
void CRC() {
current_crc_value = PRESET_VALUE;
for (i = 0; i < NUMBER_OF_BYTES; i++) {
DATA = array_of_databytes[i];
current_crc_value ^= (uint)DATA;
for (j = 0; j < 8; j++) {
if ((current_crc_value & 0x0001) > 0) {
current_crc_value >>= 1;
current_crc_value ^= MASK;
}
else {
current_crc_value >>= 1;
}
}
}
Version 2
#define PRESET_VALUE 0x6363
#define NUMBER_OF_BYTES 6
unsigned char array_of_databytes[6] = { 0x03, 0x00, 0xB0, 0x00, 0x00, 0x02 };
void CRC() {
current_crc_value = PRESET_VALUE;
for (i = 0; i < NUMBER_OF_BYTES; i++) {
DATA = array_of_databytes[i];
DATA ^= (uchar)(current_crc_value & 0x00FF);
DATA ^= (DATA<<4);
current_crc_value >>= 8;
current_crc_value ^= (uint)DATA << 8;
current_crc_value ^= (uint)DATA << 3;
current_crc_value ^= (uint)DATA >> 4;
}
}
Version 2 based on AN4420 page 20.
Both version generate a CRC 0x7940.
But according to AN4433 'Storing data into the NDEF memory of M24SR' on page 20 the CRC has to be 0x7D6B.
The databyte array
{ 0x03, 0x00, 0xB0, 0x00, 0x00, 0x02 }
contains PCB and command of the 'Read NDEF message length' command.
What could have gone wrong?
Thanks,
Jörg
