16f88 - timing-critical function for serial comm

I read on this lise that PICs have a "crappy" internal oscillator in regards to doing timing-critical functions such as serial communications.

so what is a good replacement part for the internal oscillator on a 16f88?

A three pin resonator works very well for external OSC.
But..
Microchip is claiming the internal on the 16F88 IS good enough for serial. So far I have to agree with them on this part. Other parts are not very good though...

rdxbam, you have heard correctly. "Some" of the time, the intosc will work (which is fine for hobbyists), but you cannot count on it--especially at higher speeds. M'chips spec is that they calibrate it within 1%, but my experience is to the contrary--I use enough of them to know they are regularly 3% or more out of spec, and I have seen them as bad as 6% off.

Quote:

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Originally Posted by tenaja

rdxbam, you have heard correctly. "Some" of the time, the intosc will work (which is fine for hobbyists), but you cannot count on it--especially at higher speeds. M'chips spec is that they calibrate it within 1%, but my experience is to the contrary--I use enough of them to know they are regularly 3% or more out of spec, and I have seen them as bad as 6% off.

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Normally I would agree, but MicroChip seems to have done something different with this chip.
From the F88 data sheet.

Quote:

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Addressable Universal Synchronous
Asynchronous Receiver Transmitter
(AUSART/SCI) with 9-bit address detection:
- RS-232 operation using internal oscillator
(no external crystal required)

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Like I said before, seems like they are correct. No mention of 1% +-.

Oh, and why do you think the hobby project does not have to work all of the time?

For this particular part, DS section on Electrical Characteristics 18.3 says +/- 1% typical, but as bad as +/-2 Max. I believe some of the DS's say 1% in the text of the Internal Oscillator Block section (4.5 for this one), but this particular one does not.

Hobbyists can deal with manually tuning OSCTUNE, since they are dealing with a few parts here and there, and most of the time it doesn't matter. That's not quite the same as a production environment, when all of them have to work, no matter what, and there are hundreds every day. As a hobbyist, I can throw one out (or put it in a different project) or manually tune it myself. As a manufacturer, I want less than 1% scrap, without manually tuning them. Unfortunately, M'chip does not consistently meet their spec in this regard.

I would add: you are not likely to sue yourself if failure occurs. The public ? Oh yea!

Thanks all...and a 20MHz 3-pin resonator it will be.

Thanks again for the education!