Crystal accuracy is usually 0.01% or better. Nothing else will work.
The internal oscillator is only accurate within a very narrow temp
and VDD ranges.

You can gain ONE I/O pin if you use an external oscillator.

--Bob

Edson-Jose.Martignago@invista.com wrote:

>Thank you, Jan-Erik.
>First of all, I would like to use the internal oscillator to save money=20
>and 2 I/O ports.
>
>I need to develop a frequency meter with a precision (or accuracy? or=20
>linearity? I don=B4t know the right word) of 0.1%.
>So, I think that the my base clock must have a superior precision. But I=
=20
>don=B4t know how much.
>
>The temperature of work should be between 0=BAC to 50=BAC.
>
>P.S.: Please, do you know what is the link or the name of oscillators=20
>makers?
>
>Thank you again,
>Edson Martignago.
>
>
>
>
>
>Jan-Erik Soderholm <jan-erik.soderholm@telia.com>=20
>Sent by: piclist-bounces@mit.edu
>06/01/2005 14:50
>Please respond to
>"Microcontroller discussion list - Public." <piclist@mit.edu>
>
>
>To
>piclist@mit.edu
>cc
>
>Subject
>RE: [PIC]: Internal Oscilator in 16F628
>
>
>
>
>
>
> =20
>
>>Hi,
>>I=B4m working with a 16F628, and would like to use his internal=20
>>oscillator.
>>   =20
>>
>
>Why ?
>
> =20
>
>>The Data Sheet says that the precision is +- 1%.
>>   =20
>>
>
>Right, over an limited temp range.
>
> =20
>
>>I think that this precision is not very good for my project=20
>>(frequency meter).
>>   =20
>>
>
>You are probably right there.
>
> =20
>
>>I would like to know what is the precision with a crystal oscillator=20
>>and/or resonator.
>>   =20
>>
>
>A (ceramic) resonator is probably not good enough.
>
>A crystal might be OK, but you havn't told us what stability
>and precision you need.
>See data sheets from the crystal makers.
>
>Crystal oscillators (external, canned oscs) can be found in
>just about any precision. And the price follows the precision... :-)
>See data sheets from the oscillators makers.
>
>So, what precision and temp stability do you need ?
>
>Regards,
>Jan-Erik.
>
>
>
>
> =20
>
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