8位16进制频率计的设计，其中包括测评控制电路的设计，32位锁存器的设计，32位计数器的设计和频率计顶层文件-Eight 16-band frequency of the design, including the design of the evaluation of the control circuit, 32-bit latch design, the design of 32-bit counter and frequency meter top-level document

设计一个计数器，输入计数脉冲和清零信号，输出2位16进制计数值。计数器的计数规律如下:清零信号有效时输出0，计数脉冲上升沿时，输出由0递增到ff，再递减到1，然后在递增到fe，再递减到2，再递增，按如此规律反复计数。(A counter is designed, the count pulse and the zero signal are input, and the 2 - bit 16 - digit number is output. The counting rule of the c