8251A 自收自发。采用查询方式：将内存制定区域内存放的一批数据通过8251A的TXD发送出去，然后从RXD接收回来，并在屏幕上或数码管上显示出来。-8251A since spontaneous resumption. Query: memory development of regional and storing a number of data sent through the 8251A' s TXD, and then receive back from RXD, and displayed on the screen or digital tube.