Ian Mmith wrote:
> I am using a 18F252 that can output two PWM waveforms each with it's own
> duty cycle.  However, I need three for my project.
> 
> The hardware PWM works great as you can see from this image, where it
> smoothly blends one color into another...
> 
>   http://www.ian.org/HD-Clock/HDC-BG-PWM.jpg
> 
> 
> I tried doing the PWM in software and it worked.. but not well.  I could
> only get a few bits of resolution and it ate up all the CPU cycled because
> of the high speed it needs, even with the PIC running at 40MHz.  The
> minimum period I need to use is 25us.  Higher and there is visible
> interference patterns from the PWM wave.  Just too fast to bit-bang and
> leave room for much else.
> 
> Are there any PICs that can output more than two duty cycles?  I have seen
> some PICs have four outputs but they are just for driving h-bridges and
> still only let you set two duty cycles.
> 
> I suppose I could use a 2nd PIC like a 16F86 but I'd prefer internal PWM
> since it works so well for the 2 channels I have.
> 
> Thanks!
> 
> --
> Ian Smith
> www.ian.org

Software can easily do several pwm channels; see Scott Dattalo's page,

http://www.dattalo.com/technical/software/software.php

in particular, his pwm8.asm code.  It does 8 channels of pwm in software.
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