Check the requirements of the RS232.  You might want to consider the=20
case where one unit is running at +5% and the other at -5% (if both ends=20
are the same unit).  The baud rate accuracy requirement increases with=20
baud rate, IIRC.   Also, your PWM frequency will be affected, so, the=20
pitch of your sound may vary.  The answer is in the requirements, not=20
the opinions of people who don't have the numbers.


Joe W





On 9/25/2012 1:48 AM, Lee Mulvogue wrote:
>
>
> 	I'd always read in the past to not use the internal OSC of a PIC as
> it was too innacurate, but am now wondering if this is still the case
> for a PIC24F?
>
> 	I've just started making a board based on a PIC24FJ64GA004 (my first
> time with a 24F), and added the usual 20MHz crystal and supporting
> caps; but are the modern PICs accurate enough to start considering
> dumping this external setup?  The most time sensitive thing I'm doing
> is interrupting @ 16kHz for PCM sound playback (current sample to PWM
> output, set flag for Main loop to process the next sample), and simple
> RS232 comms.  The datasheet seems to indicate a max variation of +/-
> 5%, but I don't have a benchmark to compare that against.
>
> 	I'd possibly be running the 8Mhz internal with the 4x PLL multiplier,
> resulting in 16MIPS, vs the 10MIPS of the external 20MHz crystal
> without PLL.
>
> 	Thoughts?
>
> 	Lee
>
> -------------------------
> Msg sent via Webmail - http://hosting.myob.com/
>

--=20
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