电子时钟课程设计，用汇编语言编写,键盘的扫描需要用两个输入输出端口控制，数码管的显示需要两个输出端口控制，所以可以用8255的A口和B口控制键盘-Electronic clock curriculum design, with the compilation of languages, the keyboard scanning needs with two input and output port control, LED display to control two output port