清除串口冗余。当下位机偶然有乱码出现时，在新的通讯开始先清除缓冲区冗余信号，然后开始通讯，可以保证通讯更稳健-Clear serial redundancy. Current-bit machines have occasionally garbled when, in the new communications start to clear the buffer zone redundant signal, and then began to communications, to ensure more robust communication