说明：  Atmel Mega128的BootLoader，Xmodem协议，可使用任意串口下载程序，长按‘Z’进入下载，无500ms没有接收到进入下载的信号则跳转至主程序执行
(Atmel Mega128 the BootLoader, Xmodem protocol, you can use any serial download programs, long press ' Z' into the download, no 500ms did not receive access to download the main program signal is to jump to the implementation of the)