用vhdl语言写的频率计，可以实现1khz到1Mhz，当低于1Khz时可实现测周期单位为ms，测量精度达到99 ，用数码管动态显示-Vhdl language written with the frequency meter can be achieved 1khz to 1Mhz, when less than 1Khz cycle when unit for detecting ms, 99 accuracy, dynamic display with digital control