用FPGA实现高频高精度的外部频率检测，并用1602液晶屏显示频率，用Cyclone II EP2C35F672C8N 型号的FPGA 可实现检测高达1.5M HZ的输入频率，对应的精度只有百分之0.5。-Using FPGA to realize external　frequency detection with high frequency and high precision,and use 1602 LCD screen display frequency, using the Cyclone II EP2C35F672C8N models of FPGA to realize detection of up to 1.5 M HZ input frequency and the corresponding accuracy is only zero point five percent.