编写程序，使8255的A口作为LED灯的输出，实现8位数据灯的相对循环显示。 （思考：用B口的一位作为输入，控制LED灯的循环方向。）-Written procedures so that the A port 8255 as the LED light output, 8 bits of data relative to cycle through the lamp. (Think: one with B as input port to control the direction of LED lights cycle.)