说明： 本程序是用汇编语言实现数字时钟功能的.通过修改8259中断控制器的中断屏蔽寄存器(21H号端口) 打开时间中断, 实时中断, 键盘中断 (this procedure is used assembly language digital clock function. By amending the 8259 interrupt controller interrupt masking registers (21H, port) to open the interruption time, real-time interrupt and keyboard interrupts)
