基于微机的串行通信口扩展，用8251A实现串行口异步方式单机通信，查询方式发送，中断方式接收，平时处在查询键盘，等待中断接收状态-Based on the serial communication port expansion microcomputer with 8251A serial port asynchronous communication mode single query sent, interrupt receiving, usually in the query keyboard interrupt reception wait state