VRS/Modbus.cpp

#include "Modbus.h"


void InvertUint8(unsigned char *dBuf, unsigned char *srcBuf)
{
    int i;
    unsigned char tmp[4];
    tmp[0] = 0;
    for(i = 0; i < 8; i++)
    {
        if(srcBuf[0] & (1 << i))
            tmp[0] |= 1 << (7 - i);
    }
    dBuf[0] = tmp[0];
}

void InvertUint16(unsigned short *dBuf, unsigned short *srcBuf)
{
    int i;
    unsigned short tmp[4];
    tmp[0] = 0;
    for (i = 0; i < 16; i++)
    {
        if(srcBuf[0] & (1 << i))
            tmp[0] |= 1 << (15 - i);
    }
    dBuf[0] = tmp[0];
}
unsigned short CRC16_MODBUS(unsigned char *puchMsg, unsigned int usDataLen)
{
    int i;
      unsigned short temp;
      unsigned short temp1;
    unsigned short wCRCin = 0xFFFF;
    unsigned short wCPoly = 0x8005;
    unsigned char wChar = 0;
    while(usDataLen--)
    {
        wChar = *(puchMsg++);
        InvertUint8(&wChar, &wChar);
        wCRCin ^= (wChar << 8);
        for(i = 0; i < 8; i++)
        {
            if(wCRCin & 0x8000)
                wCRCin = (wCRCin << 1)^wCPoly;
            else
                wCRCin = wCRCin << 1;
        }
    }
    InvertUint16(&wCRCin, &wCRCin);
        temp1=wCRCin>>8&0x00ff;
        temp=(temp1)+(wCRCin<<8);
    return(temp);
}