I'm working on a RFID project and it's stopped by a strange problem. When I'm trying to read a block of data, 16 byte along with 2 byte CRC is received. Then I try to calculate data CRC and compare these two, but they are not equal!

Data bytes are correct. I checked with NFC tools (Android). CRC worked fine with SAK, but not this. I wonder what the problem could be.

For details: 16 bytes are all 0x0000 and tag CRC is 0x4F68, module CRC is 0x4937

I have tried for days and found no fix for this yet.

Previous levels such as request, anti collision, select tag and authenticate were fine.

Here is the code:

unsigned short RC522::CalculateCRC(unsigned char * Data, unsigned char Dlen)
{
    CommandWrite(CMD_Idle);
    CRC_InterruptStatus();// Clear CRC interrupt and return it
    FIFO_Flush();

    for (unsigned char i = 0; i < Dlen; i++)
        FIFO_Write(Data[i]);

    CommandWrite(CMD_CalcCRC);

    for (unsigned short c = 100; c > 0; c--)
    {
        if (CRC_InterruptStatus())
            break;

        delay.Mili(1);
    }

    unsigned short Result = CRC_ResultRead();

    CommandWrite(CMD_Idle);

    return Result;
}

unsigned char RC522::ReadBlock(unsigned char Block, unsigned char * Data)
{
    unsigned char CMD[4] = {PICC_READ, Block, 0, 0};
    unsigned int Rlen;
    unsigned char Buf[18];

    unsigned short crc = CalculateCRC(CMD, 2);
    CMD[2] = crc & 0xFF;
    CMD[3] = (crc >> 8) & 0xFF;

    TX_LastBitsWrite(0);

    unsigned char Status = ToCard(CMD_Tranceive, CMD, 4, Buf, &Rlen);

    if ((Status == CARD_FOUND) && (Rlen == 144))
    {
        unsigned short crcr = (Buf[17] << 8) | Buf[16];

        crc = CalculateCRC(Buf, 16);

        if (crcr == crc) // Mismatch here !!!
        {
            for (unsigned char ptr = 0; ptr < 16; ptr++)
                Data[ptr] = Buf[ptr];

            return CARD_FOUND;
        }
    }

    return ERROR;
}