#### AliBahar

##### Member level 2

Hi friends

for DNP3 protocol crc code is generated by the following algorithm:

• Start with user data block M of k bits (k = 64 for header, 8–128 for blocks in body)

• Multiply by 65536 (ie append 16 zeros to end to form k + 16-bit number)

• Divide by generator polynomial P to obtain quotient Q and remainder R modulo-2 division is used)

• Discard Q, keep R

• Invert R to obtain R′

• Append R′ to M forming message T′ to be transmitted

Where generator polynomial:

P = x16 + x13 + x12 + x10 + x8 + x5 + x2 + 1

This forms a 17-bit number which is 13D65 (in hex)

now I have created the following C code for crc generation. but the result is not correct:

for DNP3 protocol crc code is generated by the following algorithm:

• Start with user data block M of k bits (k = 64 for header, 8–128 for blocks in body)

• Multiply by 65536 (ie append 16 zeros to end to form k + 16-bit number)

• Divide by generator polynomial P to obtain quotient Q and remainder R modulo-2 division is used)

• Discard Q, keep R

• Invert R to obtain R′

• Append R′ to M forming message T′ to be transmitted

Where generator polynomial:

P = x16 + x13 + x12 + x10 + x8 + x5 + x2 + 1

This forms a 17-bit number which is 13D65 (in hex)

now I have created the following C code for crc generation. but the result is not correct:

Code C - [expand] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 #include "stdio.h" typedef unsigned int uint; typedef unsigned char uchar; typedef unsigned long int UL; #define WIDTH (8 * sizeof(UL)) #define TOPBIT (1 << (WIDTH - 1)) UL POLYNOMIAL=0x3D650000; uint remainder = 0; uint crcGener(uint *message, uchar nSize) { uchar ff, bit; UL Rem; Rem=message[0]<<16; for (ff = 1; ff < nSize; ff++){ Rem ^=message[ff]; //printf("%x\n",Rem); for (bit = 0; bit <16; ++bit) { if (Rem & TOPBIT) { Rem = (Rem << 1) ^ POLYNOMIAL; } else { Rem = (Rem << 1); } } } /* * The final remainder is the CRC result. */ return (Rem>>16); } void main(void){ uint Msg[5]={0x0564,0x0DC4,0x0500,0x1A00,0x0000}; remainder=crcGener(Msg, 5); //printf("%x\n",remainder); getchar(); }

Last edited: