计算累加和

　　　　　/// <summary>
        /// 累加和
        /// </summary>
        /// <param name="cmd"></param>
        /// <returns></returns>
        public static byte[] SUM(byte[] cmd)
        {
            byte res = 0;
            for (int i = 0; i < cmd.Length - 1; i++)
            {
                res += cmd[i];
            }
            cmd[cmd.Length - 1] = res;
            return cmd;
        }

 1.2 求byte累加加

byte sum = (byte)0;
for (int n = 0; n < 255; n++)
{
     sum += sendBuf[n];
}