说明：  利用AT89S51 单片机的T0、T1的定时计数器功能，来完成对输入的信号进行频率计数， 计数的频率结果通过8位动态数码管显示出来。要求能够对0－250KHZ 的信号频率进行准确计数，计数误差不超过±1HZ。
(AT89S51 MCU using T0, T1 timing counter function, to complete the input signal frequency counting, counting the frequency of 8 resulted in the adoption of dynamic digital tube display. Request to the 0-250KHZ signal frequency accurately count, counting error of less than ± 1HZ.)