采用PC系统机中的8254作为中断源产生的日时钟中断，每间隔1秒在PC机屏幕上显示一行字符串“HELLO!”，按下PC机键盘的任意键退出程序。-Using the PC system in 8254 as an interrupt source generated clock interrupt every 1 second interval on the PC screen to display a line string " HELLO!" , The PC keyboard is pressed any key to exit the program.