Why would someone use an external crystal as a clock ?

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qmriso

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Hi
I have an example circuit built on a 12F675 that calls for an external 4K crystal. In a nutshell, I was wondering... "why?" [the crystal that is). I understand these chips to have an internal oscillator that can be enabled with the proper configuration word, in which case why would someone use an external crystal as a clock? Can someone explain it or point me at some explanation?

Thanks
Qmriso
 

Re: oscillation probs...

External crystal must be used if one needs precise timing. Examples:
- Baud rate genarator, if you use UART,
- sound or other frequency generation
- time interval measuremant and so on.
The 1-2% of the claimed internal generator tolerance is too bad for
such cases, especially if ambient temperature and/or power voltage
can vary.
 

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