using System;

using System.Globalization;

​

public class Program

{

    public static void Main()

    {

        //suman first convert to byte[]

        byte[] bb = ConvertHexadecimalStringToByteArray("030100AA1902");

        byte b = calculateCheckSum(bb);

            //myByte.ToString("X2")

        Console.WriteLine("returned checksum  byte= "+b);

        Console.WriteLine("returned checksum in Hexadecimal format= "+b.ToString("X2"));

    }

​

    //Following converts the hex to a byte[]

    public static byte[] ConvertHexadecimalStringToByteArray(string hexadecimalString)

    {

        if (hexadecimalString.Length % 2 != 0)

        {

            throw new ArgumentException(String.Format(CultureInfo.InvariantCulture, "HexaDecimal cannot have an odd number of digits: {0}", hexadecimalString));

        }

​

        byte[] hexByteArray = new byte[hexadecimalString.Length / 2];

        for (int index = 0; index < hexByteArray.Length; index++)

        {

            string byteValue = hexadecimalString.Substring(index * 2, 2);

            hexByteArray[index] = byte.Parse(byteValue, NumberStyles.HexNumber, CultureInfo.InvariantCulture);

        }

​

        return hexByteArray;

    }

    //calculates the checksum from the byte[] 

    private static byte calculateCheckSum(byte[] byteData)

    {

        Byte chkSumByte = 0x00;

        for (int i = 0; i < byteData.Length; i++)

            chkSumByte ^= byteData[i];

        return chkSumByte;

    }

}