Hi B,Hello,
Depends. Some pics do have internal oscillators, some don't.
Most times a crystal will be more stable as the internal oscillator.
See the datasheet of the pic for more details.
Bertus
Hi B,Hello,
The stability will depend on the quality of the crystal:
https://www.electronics-notes.com/a...rtz-crystal-xtal/crystal-resonator-ageing.php
Also the temperature stabilty will influence the frequency of the crystal.
Bertus
Hi A,My present project uses an 18.432MHz crystal. It accurately divides down for baud rates between 1200 and 115,200 and also to 1ms for a timebase.
Hi Mr C,If your project requires UART serial communications then use a crystal for frequency stability.
If you have no strict requirements with regards to frequency then you can use internal oscillator or external RC components.
BTW, when your application requires a crystal you need to be careful on how you lay out the crystal and loading capacitors on the PCB. Otherwise you may end up with wonky behaviour.
Using crystals seems straightforward but it is actually a little tricky.Hi,
I am in the habit of using crystals when making PCBs with PICs. What are the reasons for using crystals, and are they really necessary?
Camerart.
I've had no problems at all with PIC18FxxJ and K using the internal oscillator to run the USART up to 115KBaud, over 10's of thousands of units and -10C to 60C operating temperature.If your project requires UART serial communications then use a crystal for frequency stability.
Yes those scenarios are why crystals are recommended for some apps. There is also the aging issue.Here is the internal oscillator accuracy graph for the processor I'm using most lately, the PIC16F18345, where I use the internal oscillator and it seems to be fine, though obviously I'm not expecting precision timing. Basically they're claiming that you'd be in a 3-sigma band that's within 2% of nominal accuracy over the rated power supply and temperature range (except below 3V supply, it can deviate slightly more). I'm not a statistician, but I think that means it'll meet the limits 99.7% of the time, although the ominous word "typical" does appear. Maybe "typical" just means it's a variable that they can't totally control, but they're telling you the limits. It would be interesting to hear whether any units that fail to meet the 2% limit are "rogues" that you could test and discard, or whether it's a random occurrence for any particular unit (which I doubt, but there's no spec for it).
A 2% error seems to be good enough to operate a UART with another highly accurate UART and never drop bits. If a character has 10 bits, wouldn't any error have a maximum of 20% of a bit time at the end of a character? That's still an operable link. But if you had one PIC talking to another, and they were both using the internal oscillator, and one was 2% high and the other was 2% low, then it looks as if things would be pretty marginal.
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