2．　　用8251A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、中断方式接收。从键盘输入字符串（字符个数≤255）存入发送缓冲区并显示，启动发送键由实验者自己定义，自收结果显示于屏幕。按Esc返回DOS。（定义回车键为启动发送键）-2. With the 8251A Serial port asynchronous communication, spontaneous self-income, the baud rate 1200bps. Using query mode to send, receive interrupt. From the keyboard input string (character count ≤ 255) into send buffer and displays, start sending keys defined by the experimenters themselves, since the close results showed on the screen. Press Esc to return DOS. (Defined as the Enter key to start the send button)