说明：  no intro
( Signal definition: clk: standard clock signal, in this case, the frequency of 4Hz clk_1k: generating an alarm sound, the sound of the chime of the clock signal, in this case a frequency of 1024Hz mode: function control signal to 0: timing functions 1: alarm clock function 2: Manual calibration function turn: take the keys, function in the manual when school choice is to adjust the hours, or minutes if long press the button, but also to second signal cleared for precise time-setting change: access key, manually adjust the time, every time you press, the counter is incremented if long press, then in quick succession by 1, when used to quickly tune and timing hour, min, sec: The three signals are output and display hours, minutes, seconds signal using BCD code are counted separately driven six digital tube display time alert: a signal output to the speaker for generating an alarm tone chime tone alarm tone sustained 20 seconds of rapid " Didi tick" sound, if the hol)