8521实现串行通信，从键盘输入一个字符，将其ASCLL码加1后发送出去，再接收回来在屏幕上加1后的字符显示出来，实现自发自收。

-8521 serial communication, a character from the keyboard, plus one of its ASCLL code sent out, and then receive back on the screen after adding a character displayed, to achieve spontaneous self-closing.