P2口控制8个LED放光2级管的变化，包括从左到右，从右到左，从中间到两边，从两边到中间，PWM的渐亮渐灭。-P2 port to control 8 LED shine two tube changes, including from left to right, from right to left, from the middle to both sides, from both sides to the middle, PWM' s gradually getting off light.