本代码在fpga中实现了dds，程序有三个按键：一个控制产生的波形（正弦波或方波），另两个控制频率增加或降低。程序附有注释，并在signaltap中仿真成功。-The code is implemented in fpga a dds, program has three buttons: a control generated waveform (sine or square wave), the other two control the frequency increase or decr