From: Neil <picdude3@narwani.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Tue, 20 Oct 2020 09:34:46 -0700
Subject: Re: [PIC] Crystal frequency selection
Thread-Topic: [PIC] Crystal frequency selection
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Okay, I found one... 14.7456Mhz crystal --> 59.9824Mhz Fosc, which is=20
close enough to 64Mhz.
Using SPBRG =3D 127 with that gives me spot-on 115,200 baud (so 0% error).
And there are 10+ suppliers for 3.2 x 2.5mm SMD crystals with that=20
frequency so that's common enough to be low-cost and not have to worry=20
about being discontinued in the near future.
Wish I didn't have to trial and error this though.

Cheers,
-Neil.





On 10/20/2020 12:27 PM, Neil wrote:
> I had also created my own, but it's been trial-and-error (xtal freq=20
> and SPBRG value) to find a spot-on crystal.
> Now, if your spreadsheet runs through DIgikey's crystal frequency=20
> selections and picks the spot-on option for me, then you have my=20
> attention :)
>
> Cheers,
> -Neil.
>
>
>
> On 10/20/2020 12:08 PM, Nicola Perotto wrote:
>> Hi Neil & all,
>> I use the attached spreadsheet to calculate baud and errors.
>> Enter values in yellow cells.
>>       N
>>
>>
>> On 20/10/2020 16:42, Neil wrote:
>>> A bit academic, but this is bugging me... I was trying to get as close
>>> to 115,200 baud on a PIC18F running at 64Mhz (or thereabouts).
>>> At 64Mhz, best I can get is 0.8% error using SPBRG=3D34.
>>> Calculating backwards, to get exactly 115,200, I can't find an "exact"
>>> crystal.
>>> Shouldn't I be able to find one of those "odd" values to get exactly
>>> 115,200 baud at around 64Mhz?
>>>
>>> Cheers,
>>> -Neil.
>>>
>>
>>
>>
>

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