> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of RNGolding@aol.com
> Sent: 10 May 2011 14:41
> To: piclist@mit.edu
> Subject: [PIC] How to achieve 10 bit PWM resolution at various
> frequencies?
>=20
> Hi, my first request to the list, so please be gentle with me!
>=20
> I have an application that requires generation of a 10bit resolution
PWM
> signal at various repetition
> frequencies between 100Hz and 1kHz.  The PWM duty cycle and repetition
> frequency commands
> will be received via the serial bus @ 115200 baud.
>=20
> Required PWM frequencies are 105Hz, 140Hz, 300Hz and 1kHz, but other
> frequencies may be
> required in the future.
>=20
> I'm currently using a PIC18F4423 (but that can be changed if
unsuitable).
> Generating a 10bit PWM at a single frequency is pretty straightforward
> using
> a  suitable master clock frequency and Timer 2 values but
> I can't see how to get other frequencies (via PR2 value) without
losing
> the
>  10bit resolution. i.e. setting a PR2 register value below 255 to set
the
> other  frequencies reduces PWM resolution.
>=20
> I've read the data sheet 'till I'm blue in the face and can't see a
way of
> achieving 10bit resolution at the various
> frequencies.
>=20
> My present thoughts are to use two PICs. The PIC1 to generate the
required
> clock frequency for PIC2,
> which generates the 10 bit PWM (PIC2 using fixed  Timer 2 values). The
PWM
> duty cycle demand would
> then be communicated from  PIC1 to PIC2 via SPI or I2C bus.
>=20
> Clumsy, but can anyone suggest a more elegant way of doing it?


If available, you could probably use the CCP module in compare mode.
This can be configured to automatically clear or set the CCP pin on a
match condition as well as raise an interrupt.  Within the CCP interrupt
you would need to switch between these modes and reload the CCPR
registers with appropriate values for the duty cycle and frequency you
wish to operate at.

Regards

Mike

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