From: James Burkart <james@burkartstudios.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 29 Jul 2020 05:35:22 -0700
Subject: Re: [PIC] How to properly set PWM duty cycle
Thread-Topic: [PIC] How to properly set PWM duty cycle
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"What am I not getting?" Is very useful. It tells you that I don't
understand, possibly not even enough to know what information you need to
help me.

What library? I did say I'm using MCC generated functions. Do you mean you
would like to know what version of MCC?

PR2 is calculated by MCC. I'll dig through the generated code and see what
it is set to. There is something wrong with MCC: it's not showing the
proper PWM frequency. My last question to the PIC list was about that
problem.

Thanks, Nicola, for pointing me in the right direction. You're a wonderful
human bean!!

-- James



On Wed, Jul 29, 2020, 1:12 AM Nicola Perotto <nicola@nicolaperotto.it>
wrote:

> Hi James,
> find attached a small spreadsheet to do calculations.
> It confirm (part of) your calculations.
> I don't know the library you are using.
> Some info are missing:
> - code snippet, including PWM initialization
> - PR2 value (the period is calculated from this, not the inverse), my
> value is 155
> - "What am I not getting?" is actually useless... describe with details!
> Regards
>         Nicola
>
>
> On 29/07/2020 06:07, James Burkart wrote:
> > Hey, everyone!
> >
> > I am trying to figure out how to properly set the duty cycle for a PWM
> on a
> > PIC16F1503. I'm sure I am missing something obvious.
> >
> > System clock is the internal oscillator at 16MHz.
> > TMR2 prescaler is 1:64, period is set to 2.496 ms.
> > This gives the PWM a 9-bit resolution.
> >
> > The PWM frequency is 400 Hz. My goal is to be able to adjust the pulse
> > width from 1 ms to 2 ms (controlling an ESC).
> >
> > I'm using the MCC generated function:
> >
> > void PWM2_LoadDutyValue(uint16_t dutyValue)
> >
> > I was assuming that making dutyValue 512 would give me a 100% duty cycl=
e,
> > instead I get a duty cycle of around 82%.
> > A dutyValue of 624 gets me 100%, 312 gets me 50%.
> >
> > What am I not getting?
> >
> > --
> > Sincerely,
> >
> > James Burkart
> > *925.667.7175*
>
> --
>
> Nicola Perotto - NP Engineering
> Sistemi Informatici ed Elettronici
> skype: nicolap
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
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>
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