通过实验台按钮控制8251A发送数据:

连接实验台按钮SP到8255的PB0，连接8255片选CS到译码输出070；

初始化8255的PB端口为方式0；

初始化8251A：

方式命令字=异步16分频/8位/无校验/1个停止位:4EH

工作命令字=允许接收/允许发送/DTR=1/RTS=1/清除错误:37H

通过读取8255的PB的0位，检测按钮按下动作；

当按钮按下，控制8251A发送0-9的ASCII码共10个字节 ；

当程序在实验台运行，强行退出PC端DVCC软件，运行串行接口调试软件，观察确认接收数据。-Button control 8251A by test-bed to send data: SP button connected to the 8255 test-bed of PB0, connected to the decoder 8255 output of 070 CS election　initialization 8255 of the PB port mode 0　initialize the 8251A: mode command word = asynchronous divide 16/8 bit/no parity/1 stop bit: 4EH word = work order to allow the reception/allowed to send/DTR = 1/RTS = 1/Clear the error: 37H PB-8255 by reading bit 0 Press the test button action　when the button is pressed, the control 8251A 0-9 ASCII code sent a total of 10 bytes　when the program runs in the test bed, forced to exit PC-DVCC software, run the serial interface debugging software, observation confirmed receiving data.