当外加时钟信号的频率为1HZ,要求秒表能精确到1秒.该秒表具有异步清零(CLK)功能和计数使能控制信号(EN).高电平有效,输出结果显示在数码管上.

 框图如下:

                     译码显示                      译码显示  
                         i                           i
                         i                           i
                         i                           i
                         i                           i
   1HZ  ---------    秒钟个位  ----------------   秒钟十位
                     (十进制计数器)            (六进制计数器)