Post by thread:[PIC]: 18F 8MHz internal oscillators

So....not to get off topic but back to topic... Ignoring for the moment the discussion about the UARTs that has gone on... I take it that the internal oscillators that Mchip has internal are just as good as putting an external crystal and associated parts. __________________________________ Do you Yahoo!? Yahoo! Mail - You care about security. So do we. http://promotions.yahoo.com/new_mail

On Fri, 4 Feb 2005 10:24:58 -0800 (PST), alan smith <spam_OUTmicro_eng2TakeThisOuTyahoo.com> wrote: > So....not to get off topic but back to topic... > > Ignoring for the moment the discussion about the UARTs > that has gone on... > > I take it that the internal oscillators that Mchip has > internal are just as good as putting an external > crystal and associated parts. > Not just as good... but good enough for serial communications, at least in my experience. Regards, Mark markrages@gmail -- "We act as though comfort and luxury were the chief requirements of life, when all that we need to make us happy is something to be enthusiastic about." - Einstein

alan smith wrote : > I take it that the internal oscillators that Mchip has > internal are just as good as putting an external > crystal and associated parts. It might be "just as good" in some ways, but it might also be "not as good" in other ways and sometimes even "better then" (such as "less components") in yet other ways. Depending on what's important for you, you should look up and evaluate whatever electrical specification in the data sheet that might apply to your specific project. When it comes to freq stability/precision it's probably OK at 25 deg C and otherwise "normal" conditions to run the USART. But probably not over the full temp range of the device. And also, it (INTOSC) might be "just as good" to normal hobbyists standards, bot not if building a larger series of (professional) products. Regards, Jan-Erik.

> Not just as good... but good enough for serial communications, at > least in my experience. note for the reader: this does not realy contradict my opinion that 'I would not trust it' :) Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: http://www.voti.nl/hvu

> I take it that the internal oscillators that Mchip has > internal are just as good as putting an external > crystal and associated parts. They are very good at oscillating, but the frequnecy accuracy will not match a resonator, much less a crystal. Whether it is sufficient for your application depends on what you need. Last time I checked I would not yet use them for asynch. Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: http://www.voti.nl/hvu

> -----Original Message----- > From: .....piclist-bouncesKILLspam@spam@mit.edu On Behalf Of alan smith > Sent: Friday, February 04, 2005 1:25 PM > > So....not to get off topic but back to topic... > > Ignoring for the moment the discussion about the UARTs > that has gone on... > > I take it that the internal oscillators that Mchip has > internal are just as good as putting an external > crystal and associated parts. A cheap low quality crystal @ 25degC is accurate to +/-0.01% the internal oscillator of the PIC18F1220 is specified as +/-2% a huge difference in accuracy. For async serial comms I agree with what Wouter said in an earlier post on this thread: "I dunno how you meant this, but in my opinion 3% is the maximum error I would accept in the whole chain: sender, electronics, receiver. The error in the internal oscillator *and* the error listed for the baudrate divisor add up to the error at the sender, which I would not allocate more than 1%." With +/-2% error in the internal oscillator (+/-5% over temperature), I would not use it in a commercial product. However the typical error from the spec sheet is +/-1% so, for a hobby project it should be OK. Paul Hutch

Wouter van Ooijen wrote: > They are very good at oscillating, but the frequnecy accuracy will not > match a resonator, much less a crystal. Whether it is sufficient for > your application depends on what you need. Last time I checked I would > not yet use them for asynch. Some of the newer ones are more accurate. If I remember right, 1% at 25degC, 2% over full temperature range. That is good enough to do RS-232 if the other end has a known accurate clock. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com

Excellent....thanks very much. Crystal goes into the board. --- Wouter van Ooijen <wouterKILLspamvoti.nl> wrote: {Quote hidden}> > I take it that the internal oscillators that Mchip > has > > internal are just as good as putting an external > > crystal and associated parts. > > They are very good at oscillating, but the frequnecy > accuracy will not > match a resonator, much less a crystal. Whether it > is sufficient for > your application depends on what you need. Last time > I checked I would > not yet use them for asynch. > > Wouter van Ooijen > > -- ------------------------------------------- > Van Ooijen Technische Informatica: http://www.voti.nl > consultancy, development, PICmicro products > docent Hogeschool van Utrecht: http://www.voti.nl/hvu > > > --