The function only expects values between 0 and 255.
Weedpharma
Buddy, I can't click in the link, maybe the reason is my location, China. Sorry, I see the detail information about function analogWrite, thanks a lot.
If you're willing to poke at registers instead of using analogWrite(), you can make the '328p output 16-bit PWM (0 ~ 65535 ) instead of 8-bit (0~255) on two channels - timer1 is 16-bit - if you need more precise control over the duty cycle