做一个基于STC89C52RC的简易的单片机数字钟。该数字钟有8个共阴极的七段数码管，通过切换可以分别显示时间，日期以及闹钟设置。-Do a STC89C52RC based on the simple single-chip digital clock. The digital clock has eight of the cathode tube seven segment digital, through the switch can respectively show the time, date and set the alarm clock.