private static string AddChecksum(string s)
Console.WriteLine(chksum);
s = "$" + s + "*" + chksum.ToString("X2") + ((char)13).ToString() + ((char)10).ToString();
public static void Main()
string stcMsg = "SNSTC,-100,1";
string rdrMsg = "SNRSA,-4, A,-4, A";
Console.WriteLine(AddChecksum(rdrMsg));