说明：  1.单机自发自收串行通信。接收键入字符，从8251A的发送端发送，与同一个8251A的接收端接收，然后在屏幕上显示出来。 2.双机串行通信，在一台PC机键入字符，从8251A的发送端发送给另一台PC机，另一台PC机的 8251A的接收端接收，然后在屏幕上显示出来。
(1. Since the resumption of spontaneous stand-alone serial communication. Type the characters receive from the sending end to send the 8251A, 8251A with the receiving end of a receiver, and then displayed on the screen. 2. Dual serial communication, in a PC-type characters, from the sending end 8251A sent to another PC, another PC-8251A to receive the receiving end, and then displayed on the screen.)