PWM period = [(PR) + 1] * 4 * TOSC * (TMR2 prescale value)

The maximum is when PR and TMR2 prescaler are at their highest values:
Longest PWM Period = [1023 + 1] * 4 * [ 1 / 4,000,000 ] * 16

Which is a period of 0.016384, and a frequency of 61.035.  Should be
just fine for servo use.

Check those equations, though - I've never used the PWM and am just
giving you a hold-over answer until someone who does use them with
servos can answer.  I took this from the f877 data sheet, Page 61.

It may actually be easier to do this with an interrupt anyway - there
are several servo routines out there, and a few multiple servo routines
(need to run 8 servos from one PIC?)

-Adam

Andy Shaw wrote:

>Hi,
>What is the lowest frequency you can get using the PWM module (on say an
>16F877 with 4MHz xtal)? From looking at the docs it seems to me it is
>1000000/16/256  which is approx 244Hz. Is this correct I've been thinking of
>using the PWM module to generate a standard R/C servo control pulse but this
>has a frequency of 50Hz. I've not really used the PWM module before so just
>exploring options at the moment. Failing this any other ways of using the
>hardware to generate the pulse train. I've used the CCP module to do it but
>that still involves code to start the process off every 20ms or so.
>
>Thanks
>
>Andy
>
>--
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>
>
>
>
>
>
>

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