设计一数字 频率计，其技术要求如下： (1)　　测量频率范围：1Hz~100kHz。 (2)　　准确度Dfx/fx£ ± 2%。 (3)　　测量信号：方波，峰峰值为3V~5V。-design a figure frequency meter, the technical requirements are as follows : (a) measuring frequency range : 1Hz - 100kHz. (2) the accuracy Dfx / fxpound 2%. (3) Measurement of signal : square wave peak to peak for 3V to 5V.