2019-06-04 C# Modbus RTU CRC

We need calcuate the crc of Modbus RTU in C#

There is a tool to validate the crc value

My test code

...
        static byte[] var_ComData = new byte[256];
        static int var_ComDataLength = 0;
        static byte[] var_ComDataCRC = new byte[2];
...
...
        private void CalculateCRC()
        {
            ushort CRCFull = 0xFFFF; // CRC 的初值設成 0xFFFF
            byte CRCHigh = 0xFF, CRCLow = 0xFF; // CRC 的 High byte 和 Low byte
            char CRCLSB; // CRC Least signficant bit

            for (int i=0; i < var_ComDataLength; i++)
            {
                CRCFull = (ushort)(CRCFull ^ var_ComData[i]); // exclusive or 
                for (int j = 0; j < 8; j++)
                {
                    CRCLSB = (char)(CRCFull & 0x0001); // 取得 Least signficant bit
                    CRCFull = (ushort)((CRCFull >> 1) & 0x7FFF); // 移去 Least signficant bit，前補0

                    if (CRCLSB == 1) // 如果 Least signficant bit 為 1
                        CRCFull = (ushort)(CRCFull ^ 0xA001);
                }
            }
            var_ComDataCRC[1] = CRCHigh = (byte)((CRCFull >> 8) & 0xFF); // CRC high byte 在 後
            var_ComDataCRC[0] = CRCLow = (byte)(CRCFull & 0xFF); // CRC low byte 在前
        }
   ...

In this page https://home.gamer.com.tw/creationDetail.php?sn=3659934

There is a tool can calculate the CRC

Download Link

In this site

There is a on line calculator for CRC calculate

374 person(s) visited this page until now.

Back