modbus crc c#

Modbus协议支持两种传输方式，命令结构:

ASCII模式
    : 地址 功能代码 数据数量 数据1 ... 数据n LRC高字节 LRC低字节 回车 换行

RTU模式
    地址 功能代码 数据数量 数据1 ... 数据n CRC高字节 CRC低字节

ASCII为LRC效验方式，C#代码如下：

public string getLRC(string str)
        {
            int d_lrc = 0;
            string h_lrc = "";
            int k = str.Length;
            for (int i = 0; i < k; i = i + 2)
            {
                string i_data = str.Substring(i, 2);
                d_lrc = d_lrc + Convert.ToInt32(i_data);
            }
            if (d_lrc >= 16)
                d_lrc = d_lrc % 16;
            h_lrc = Convert.ToInt32(~d_lrc + 1).ToString("X");
            if (h_lrc.Length > 2)
                h_lrc = h_lrc.Substring(h_lrc.Length - 2, 2);
            return h_lrc;
        }

RTU为CRC效验方式，C#代码如下：

private static void CalculateCRC(byte[] pByte, int nNumberOfBytes, out byte hi, out byte lo)
        {
            ushort sum;
            CalculateCRC(pByte, nNumberOfBytes, out sum);
            lo = (byte)(sum & 0xFF);
            hi = (byte)((sum & 0xFF00) >> 8);
        }

private static void CalculateCRC(byte[] pByte, int nNumberOfBytes, out ushort pChecksum)
        {
            int nBit;
            ushort nShiftedBit;
            pChecksum = 0xFFFF;

            for (int nByte = 0; nByte < nNumberOfBytes; nByte++)
            {
                pChecksum ^= pByte[nByte];
                for (nBit = 0; nBit < 8; nBit++)
                {
                    if ((pChecksum & 0x1) == 1)
                    {
                        nShiftedBit = 1;
                    }
                    else
                    {
                        nShiftedBit = 0;
                    }
                    pChecksum >>= 1;
                    if (nShiftedBit != 0)
                    {
                        pChecksum ^= 0xA001;
                    }
                }
            }
        }