MODBUS RTU CRC16 Berechnung

Question

Ich kodiere einen MODBUS CRC16 Rechner in C. Was ich vorher habe ist ein Python, der das macht, ich wollte es in C umwandeln. Ich habe einige Codes online gefunden, aber es gibt mir nicht die richtige Antwort .

Für meine Python-Code, ich habe dies als meine CRC16.py

#!/usr/bin/env python 

def calc(data): 
     crc_table=[0x0000,0xC0C1,0xC181,0x0140,0xC301,0x03C0,0x0280,0xC241,0xC601,0x06C0,0x0780,0xC741,0x0500,0xC5C1,0xC481,0x0440,0xCC01,0x0CC0,0x0D80,0xCD41,0x0F00,0xCFC1,0xCE81,0x0E40,0x0A00,0xCAC1,0xCB81,0x0B40,0xC901,0x09C0,0x0880,0xC841,0xD801,0x18C0,0x1980,0xD941,0x1B00,0xDBC1,0xDA81,0x1A40,0x1E00,0xDEC1,0xDF81,0x1F40,0xDD01,0x1DC0,0x1C80,0xDC41,0x1400,0xD4C1,0xD581,0x1540,0xD701,0x17C0,0x1680,0xD641,0xD201,0x12C0,0x1380,0xD341,0x1100,0xD1C1,0xD081,0x1040,0xF001,0x30C0,0x3180,0xF141,0x3300,0xF3C1,0xF281,0x3240,0x3600,0xF6C1,0xF781,0x3740,0xF501,0x35C0,0x3480,0xF441,0x3C00,0xFCC1,0xFD81,0x3D40,0xFF01,0x3FC0,0x3E80,0xFE41,0xFA01,0x3AC0,0x3B80,0xFB41,0x3900,0xF9C1,0xF881,0x3840,0x2800,0xE8C1,0xE981,0x2940,0xEB01,0x2BC0,0x2A80,0xEA41,0xEE01,0x2EC0,0x2F80,0xEF41,0x2D00,0xEDC1,0xEC81,0x2C40,0xE401,0x24C0,0x2580,0xE541,0x2700,0xE7C1,0xE681,0x2640,0x2200,0xE2C1,0xE381,0x2340,0xE101,0x21C0,0x2080,0xE041,0xA001,0x60C0,0x6180,0xA141,0x6300,0xA3C1,0xA281,0x6240,0x6600,0xA6C1,0xA781,0x6740,0xA501,0x65C0,0x6480,0xA441,0x6C00,0xACC1,0xAD81,0x6D40,0xAF01,0x6FC0,0x6E80,0xAE41,0xAA01,0x6AC0,0x6B80,0xAB41,0x6900,0xA9C1,0xA881,0x6840,0x7800,0xB8C1,0xB981,0x7940,0xBB01,0x7BC0,0x7A80,0xBA41,0xBE01,0x7EC0,0x7F80,0xBF41,0x7D00,0xBDC1,0xBC81,0x7C40,0xB401,0x74C0,0x7580,0xB541,0x7700,0xB7C1,0xB681,0x7640,0x7200,0xB2C1,0xB381,0x7340,0xB101,0x71C0,0x7080,0xB041,0x5000,0x90C1,0x9181,0x5140,0x9301,0x53C0,0x5280,0x9241,0x9601,0x56C0,0x5780,0x9741,0x5500,0x95C1,0x9481,0x5440,0x9C01,0x5CC0,0x5D80,0x9D41,0x5F00,0x9FC1,0x9E81,0x5E40,0x5A00,0x9AC1,0x9B81,0x5B40,0x9901,0x59C0,0x5880,0x9841,0x8801,0x48C0,0x4980,0x8941,0x4B00,0x8BC1,0x8A81,0x4A40,0x4E00,0x8EC1,0x8F81,0x4F40,0x8D01,0x4DC0,0x4C80,0x8C41,0x4400,0x84C1,0x8581,0x4540,0x8701,0x47C0,0x4680,0x8641,0x8201,0x42C0,0x4380,0x8341,0x4100,0x81C1,0x8081,0x4040] 

     crc_hi=0xFF 
     crc_lo=0xFF 

     for w in data: 
       index=crc_lo^ord(w) 
       crc_val=crc_table[index] 
       crc_temp=crc_val/256 
       crc_val_low=crc_val-(crc_temp*256) 
       crc_lo=crc_val_low^crc_hi 
       crc_hi=crc_temp 

     crc=crc_hi*256 +crc_lo 
     return crc 

Als nächstes ich ein Skript zur Eingabe verwenden werden meine Variablen:

import math 
import subprocess 
import serial 
import time 
from time import sleep 
import struct 
import CRC16 
import sys 

address = chr(0x01) 
function_code = chr(0x04) 
start_at_reg = chr(0x10) + chr(0x06) 
num_of_reg = chr(0x00) + chr(0x02) 



read_device = address + function_code + start_at_reg + num_of_reg 
crc = CRC16.calc(read_device) 
crc_hi = crc/256 
crc_lo = crc & 0xFF 
print "meter add: " +str(ord(address)) 
print "crc_lo: " +str(hex(crc_lo)) 
print "crc_hi: " +str(hex(crc_hi)) 

Das wird mir geben:

>> 
meter add: 1 
crc_lo: 0x95 
crc_hi: 0xa 

Nun fand ich diese C-Code online, die CRC16 zu berechnen:

WORD CRC16 (const BYTE *nData, WORD wLength) 
{ 
static const WORD wCRCTable[] = {0x0000,0xC0C1,0xC181,0x0140,0xC301,0x03C0,0x0280,0xC241,0xC601,0x06C0,0x0780,0xC741,0x0500,0xC5C1,0xC481,0x0440,0xCC01,0x0CC0,0x0D80,0xCD41,0x0F00,0xCFC1,0xCE81,0x0E40,0x0A00,0xCAC1,0xCB81,0x0B40,0xC901,0x09C0,0x0880,0xC841,0xD801,0x18C0,0x1980,0xD941,0x1B00,0xDBC1,0xDA81,0x1A40,0x1E00,0xDEC1,0xDF81,0x1F40,0xDD01,0x1DC0,0x1C80,0xDC41,0x1400,0xD4C1,0xD581,0x1540,0xD701,0x17C0,0x1680,0xD641,0xD201,0x12C0,0x1380,0xD341,0x1100,0xD1C1,0xD081,0x1040,0xF001,0x30C0,0x3180,0xF141,0x3300,0xF3C1,0xF281,0x3240,0x3600,0xF6C1,0xF781,0x3740,0xF501,0x35C0,0x3480,0xF441,0x3C00,0xFCC1,0xFD81,0x3D40,0xFF01,0x3FC0,0x3E80,0xFE41,0xFA01,0x3AC0,0x3B80,0xFB41,0x3900,0xF9C1,0xF881,0x3840,0x2800,0xE8C1,0xE981,0x2940,0xEB01,0x2BC0,0x2A80,0xEA41,0xEE01,0x2EC0,0x2F80,0xEF41,0x2D00,0xEDC1,0xEC81,0x2C40,0xE401,0x24C0,0x2580,0xE541,0x2700,0xE7C1,0xE681,0x2640,0x2200,0xE2C1,0xE381,0x2340,0xE101,0x21C0,0x2080,0xE041,0xA001,0x60C0,0x6180,0xA141,0x6300,0xA3C1,0xA281,0x6240,0x6600,0xA6C1,0xA781,0x6740,0xA501,0x65C0,0x6480,0xA441,0x6C00,0xACC1,0xAD81,0x6D40,0xAF01,0x6FC0,0x6E80,0xAE41,0xAA01,0x6AC0,0x6B80,0xAB41,0x6900,0xA9C1,0xA881,0x6840,0x7800,0xB8C1,0xB981,0x7940,0xBB01,0x7BC0,0x7A80,0xBA41,0xBE01,0x7EC0,0x7F80,0xBF41,0x7D00,0xBDC1,0xBC81,0x7C40,0xB401,0x74C0,0x7580,0xB541,0x7700,0xB7C1,0xB681,0x7640,0x7200,0xB2C1,0xB381,0x7340,0xB101,0x71C0,0x7080,0xB041,0x5000,0x90C1,0x9181,0x5140,0x9301,0x53C0,0x5280,0x9241,0x9601,0x56C0,0x5780,0x9741,0x5500,0x95C1,0x9481,0x5440,0x9C01,0x5CC0,0x5D80,0x9D41,0x5F00,0x9FC1,0x9E81,0x5E40,0x5A00,0x9AC1,0x9B81,0x5B40,0x9901,0x59C0,0x5880,0x9841,0x8801,0x48C0,0x4980,0x8941,0x4B00,0x8BC1,0x8A81,0x4A40,0x4E00,0x8EC1,0x8F81,0x4F40,0x8D01,0x4DC0,0x4C80,0x8C41,0x4400,0x84C1,0x8581,0x4540,0x8701,0x47C0,0x4680,0x8641,0x8201,0x42C0,0x4380,0x8341,0x4100,0x81C1,0x8081,0x4040}; 

BYTE nTemp; 
WORD wCRCWord = 0xFFFF; 

    while (wLength--) 
    { 
     nTemp = *nData++^wCRCWord; 
     wCRCWord >>= 8; 
     wCRCWord ^= wCRCTable[nTemp]; 
    } 
    return wCRCWord; 

} 

Ich speicherte diesen Code als Header-Datei, "CRC.h". So kann ich die Daten eingeben, die ich habe:

#include <stdio.h> 
#include <string.h> 
#include <unistd.h> 
#include <fcntl.h> 
#include <errno.h> 
#include <termios.h> 
#include <stdint.h> 
#include <inttypes.h> 
#include <stdlib.h> 
#ifdef WIN32 
/*windows stuff*/ 
#else 
    typedef unsigned long WORD; 
    typedef unsigned char BYTE; 
#endif 
#include "CRC.h" 

int main(){ 
    char query_m[6]; 
    char add = 0x01; 
    char fnc_code = 0x04; 
    char reg_hi = 0x10; 
    char reg_lo = 0x06; 
    char num_hi = 0x00; 
    char num_lo = 0x02; 
    query_m[0] = add; 
    query_m[1] = fnc_code; 
    query_m[2] = reg_hi; 
    query_m[3] = reg_lo; 
    query_m[4] = num_hi; 
    query_m [5] = num_lo; 
    int i; 
    for(i=0;i<7; i++){ 
     printf("this is query_m[%d]: %d\n", i, query_m[i]); 

    } 
    int size_m = 7; 
    char crc_data; 

    crc_data = CRC16(query_m, sizeof(query_m)); 
    printf("this is CRC: %d\n", crc_data); 
    return 0; 
} 

Das gibt mir einen Wert von -107. Ich bin relativ neu in C, und ich mache immer noch einige Experimente zu diesem

Vielen Dank.

Answer 1

• WORD sollte unsigned short (2 Bytes), nicht unsigned long (4 oder 8 Bytes auf der Plattform abhing)

  typedef unsigned short WORD; 
  

• @paddy Wie gesagt, loop 0-6 in der for-Schleife:

  for (i=0; i<6; i++) { 
      ... 
  } 
  

• crc_data sollte WORD vom Typ sein, nicht char

  WORD crc_data; 
  

• Verwendung %04x in letzter printf()

  printf("this is CRC: %04x\n", crc_data);