设计一个具有时、分、秒计时的电子钟，按24小时计时。要求：
（1）数字钟的时间用六位数码管分别显示时、分、秒；
（2）用两个控制键，对数字钟分别进行分、时校正；
（3）具有仿广播电台整点报时的功能。即每逢59分51秒、53秒、55秒及57秒时，发出4声500Hz低音，在59分59秒时发出一声1kHz高音，它们的持续时间均为1秒。最后一声高音结束的时刻恰好为正点时刻。
（4）具有定时闹钟功能，且最长闹铃时间为1分钟。要求可以任意设置闹钟的时、分；闹铃信号为500Hz和1kHz的方波信号，两种频率的信号交替输出，且均持续1秒。设置一个停止闹铃控制键，可以停止输出闹铃信号。
（5）输入时钟脉冲的频率为50MHz。(Design an electronic clock with time, minutes and seconds, and time by 24 hours. Requirements:
(1) the time of digital clock is shown with six digital tubes, respectively, minutes and seconds;
(2) two control keys are used to divide and adjust the digital clock respectively.
(3) it has the function of imitating radio station. That means that at 59 minutes, 51 seconds, 53 seconds, 55 seconds and 57 seconds, a 4 500Hz bass is emitted. A 1kHz note is emitted at 59 minutes 59 seconds, and their duration is 1 second. The end of the last treble is exactly the moment of truth.
(4) it has a timer function and the longest alarm time is 1 minute. Ask to set the alarm clock at any time. The alarm signal is a square wave signal of 500Hz and 1kHz. The signals of both frequencies alternate and output for one second. Set a stop alarm button to stop the output alarm signal.
(5) the frequency of input clock pulse is 50MHz.)