实现PWM 输出控制LED 显示。通过这个实验，掌握采用Verilog HDL 语言 编程实现PWM 输出控制LED 的显示方法以及PWM 控制的工作原理。-PWM output to control LED display. Through this experiment, master PWM output to control LED display as well as the works of the PWM control using Verilog HDL language p