Example Description

This example describes how to use PWM.

Requirement Components:
    1~4 LED

Connect LED to below PWM pins and GND, then the LED will gradually become brighter and then darker with different speed.
    1, connect PF_6 to a LED and GND in series
    2, connect PF_7 to a LED and GND in series
    3, connect PF_8 to a LED and GND in series
    4, connect PF_9 to a LED and GND in series


