说明：  数字秒表的VHDL代码。当设计文件加载到目标器件后，设计的数字秒表从00-00-00开始计秒。，直到按下停止按键（按键开关S2）。数码管停止计秒。按下开始按键（按键开关S1），数码管继续进行计秒。按下复位按键（核心板上复位键）秒表从00-00-00重新开始计秒。
(The VHDL code for digital stopwatch. When the design document loaded into the target device, the designed digital stopwatch count the seconds from the 00-00-00. Until you press stop key (key switch S2). Nixie tube stop count seconds. Press the start button (key switch S1), the digital control continue to count seconds. Press the reset button (core panel reset button) to restart the stopwatch count seconds from the 00-00-00.)