Calculation error with CRC-16

Projects Programming
1

Hi. I am trying to implement the CRC-16 algorithm with Arduino, for this I have a string as input, which I convert into a hex array, I apply uppercase and after I try to apply the CRC-16/xmodem calculation algorithm, but the the result I get is 0x9568, when it should be 0x08E2.

Apparently the algorithm is correct because when I directly apply a hex array as input, the correct value is obtained as a result.

Here is my code:

char stringArray[] = "Hello Word!";
char HexStringArray[sizeof(stringArray) * 2 + 1];
byte myData[sizeof(stringArray) * 2 + 1];

static const unsigned short crc16tab[256]= {
	0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
	0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,
	0x1231,0x0210,0x3273,0x2252,0x52b5,0x4294,0x72f7,0x62d6,
	0x9339,0x8318,0xb37b,0xa35a,0xd3bd,0xc39c,0xf3ff,0xe3de,
	0x2462,0x3443,0x0420,0x1401,0x64e6,0x74c7,0x44a4,0x5485,
	0xa56a,0xb54b,0x8528,0x9509,0xe5ee,0xf5cf,0xc5ac,0xd58d,
	0x3653,0x2672,0x1611,0x0630,0x76d7,0x66f6,0x5695,0x46b4,
	0xb75b,0xa77a,0x9719,0x8738,0xf7df,0xe7fe,0xd79d,0xc7bc,
	0x48c4,0x58e5,0x6886,0x78a7,0x0840,0x1861,0x2802,0x3823,
	0xc9cc,0xd9ed,0xe98e,0xf9af,0x8948,0x9969,0xa90a,0xb92b,
	0x5af5,0x4ad4,0x7ab7,0x6a96,0x1a71,0x0a50,0x3a33,0x2a12,
	0xdbfd,0xcbdc,0xfbbf,0xeb9e,0x9b79,0x8b58,0xbb3b,0xab1a,
	0x6ca6,0x7c87,0x4ce4,0x5cc5,0x2c22,0x3c03,0x0c60,0x1c41,
	0xedae,0xfd8f,0xcdec,0xddcd,0xad2a,0xbd0b,0x8d68,0x9d49,
	0x7e97,0x6eb6,0x5ed5,0x4ef4,0x3e13,0x2e32,0x1e51,0x0e70,
	0xff9f,0xefbe,0xdfdd,0xcffc,0xbf1b,0xaf3a,0x9f59,0x8f78,
	0x9188,0x81a9,0xb1ca,0xa1eb,0xd10c,0xc12d,0xf14e,0xe16f,
	0x1080,0x00a1,0x30c2,0x20e3,0x5004,0x4025,0x7046,0x6067,
	0x83b9,0x9398,0xa3fb,0xb3da,0xc33d,0xd31c,0xe37f,0xf35e,
	0x02b1,0x1290,0x22f3,0x32d2,0x4235,0x5214,0x6277,0x7256,
	0xb5ea,0xa5cb,0x95a8,0x8589,0xf56e,0xe54f,0xd52c,0xc50d,
	0x34e2,0x24c3,0x14a0,0x0481,0x7466,0x6447,0x5424,0x4405,
	0xa7db,0xb7fa,0x8799,0x97b8,0xe75f,0xf77e,0xc71d,0xd73c,
	0x26d3,0x36f2,0x0691,0x16b0,0x6657,0x7676,0x4615,0x5634,
	0xd94c,0xc96d,0xf90e,0xe92f,0x99c8,0x89e9,0xb98a,0xa9ab,
	0x5844,0x4865,0x7806,0x6827,0x18c0,0x08e1,0x3882,0x28a3,
	0xcb7d,0xdb5c,0xeb3f,0xfb1e,0x8bf9,0x9bd8,0xabbb,0xbb9a,
	0x4a75,0x5a54,0x6a37,0x7a16,0x0af1,0x1ad0,0x2ab3,0x3a92,
	0xfd2e,0xed0f,0xdd6c,0xcd4d,0xbdaa,0xad8b,0x9de8,0x8dc9,
	0x7c26,0x6c07,0x5c64,0x4c45,0x3ca2,0x2c83,0x1ce0,0x0cc1,
	0xef1f,0xff3e,0xcf5d,0xdf7c,0xaf9b,0xbfba,0x8fd9,0x9ff8,
	0x6e17,0x7e36,0x4e55,0x5e74,0x2e93,0x3eb2,0x0ed1,0x1ef0
};
  
unsigned short crc16_ccitt(const void *buf, int len){
	register int counter;
	register unsigned short crc = 0;
	for( counter = 0; counter < len; counter++)
		crc = (crc<<8) ^ crc16tab[((crc>>8) ^ *(char *)buf++)&0x00FF];
	return crc;
}
void setup(){
  Serial.begin(115200);
  for (int i = 0; i < strlen(stringArray); i++)  {
    sprintf(&HexStringArray[i * 2], "%02x", stringArray[i]);
  }
	for (uint8_t cnt = 0; cnt <= strlen(HexStringArray); cnt++) {
    HexStringArray[cnt] = toupper(HexStringArray[cnt]);
  }
   Serial.println(HexStringArray);
   Serial.println(crc16_ccitt(HexStringArray,strlen(HexStringArray)), HEX);
}
void loop(){}
2

Why do you make that weird conversion array to hex? It is absolutely wrong way.

You should calculate CRC from initial data.
Try just this:

3

why are you directly referencing crctab inside this function instead of "buf" which is presumably the argument it should operate on?

and is the function operating on a byte, short or void* size array?

4

I would not know what to answer you, this is not my code, I took it from here here

5

To get the 0x08E2 answer have to do the CRC calculation on the ASCII "Hello Word!", not on the ASCII of the hexadecimal of the ASCII.

6

no, the buf argument is for input data array, for example for "Hello Word!"

7

@medusa
Can you explain, why do you convert your initial array to "hexadecimal ASCII" ?

I just tested - If I apply the CRC calculation function to the original data "Hello Word!", as I wrote in post#2, it returns exactly 0x08E2.

8

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