通过PWM定时器延迟一秒，实现一个LED灯的明灭。实验中观察I/O口的值对LED灯的明灭的控制，学习I/O口的输入输出方式和设置，了解PWM的配置方式-Through the PWM timer to delay a second, the realization of a LED lamp at. I/O values for LED lamp light control experiment, learning I/O port input and output method and set