from machine import Pin, PWM            #引入module:machine，在此只引入"Pin，PWM"功能
import time                             #引入module:time
ledpin = Pin(20,Pin.OUT)
LED = PWM(ledpin)

while True:
    for i in range(1023):
        LED.duty(i)
        time.sleep_ms(5)
        print('Now i is,',str(i))
    for i in range(1023):
        LED.duty(1023-i)
        time.sleep_ms(5)
        print('Now i is,',str(1023-i))