用8251实现串行口异步通信，自发自收，波特率1200bps。采用查询方式发送与接收。从键盘输入发送字符。发送与接收的字符均在屏幕上显示。按esc键返回dos-Achieved with the 8251 serial asynchronous communication, spontaneous self-income, the baud rate 1200bps. Way to send and receive using queries. To send characters from the keyboard. Send and receive characters are displayed on the screen. Press esc key to return to dos