Osctune

[Heckler]

Thanks rmteo,

So is it correct to say that the PIC's I mentioned DO have the OSCTUNE register that the user can manually adjust to calibrate the oscillator. But they do not come from the factory with an OSCCAL value stored in memory.

How did you know that these chips do not come with this OSCAL value?

At what level DO the chips come with this calibration value?

Thanks again
Just trying to learn and understand

Dwight

[rmteo]

Yes, all 3 of the PIC's you mentioned have an OSCTUNE register that allow you to adjust the frequency. As such, they do not have (or need) an OSCCAL.

The best place to get this info is from the device data sheet. Only the low end PIC10's (and some PIC12's) with 12-bit instruction words have the OSCCAL register. They also do not have an OSCTUNE register.

[languer]

How did you know that these chips do not come with this OSCAL value?

Read the datasheet - it's all there (no OSCCAL reg, but OSCTUNE reg).

Adding to rmteo's comments; none of the new chips (except the 10Fs) have OSCCAL. Reason is quite simple, they come trimmed from the factory; which makes their specs more tight than the ones with an OSCCAL reg. You can "tune" them if needed, but no real need to calibrate. If you place any of the newer chips on a frequency meter (one with a good reference); you'll notice they track pretty good. You only need to "tune" them if you need to track another free-running oscillator (read as if in RS232 clock/baud generator, etc), or want much better performance over temperature. The older chips with OSCCAL register were calibrated from the factory but their specs were looser and they could easily be erased (this was a big source of complaints).

At what level DO the chips come with this calibration value?

Older chips or lower end chips (10Fs) have the OSCCAL reg. You would much prefer the OSCTUNE register to the OSCCAL one (if given the choice).

[Heckler]

Thanks Languer,

That helps alot!! So the fact is that the chips that I am using are actually later generation chips with the OSCTUNE (and better quality internal oscillators).

I do have the datasheets and did do a search for both OSCCAL and OSCTUNE. I obviously found the latter not the former. I did not realize that OSCTUNE and OSCCAL were not the same thing, just stated differently, now I do.

Older chips or lower end chips (10Fs) have the OSCCAL reg. You would much prefer the OSCTUNE register to the OSCCAL one (if given the choice).

This one statement helps a bunch.

If there has been one thing I have had to learn over the past year or so is to always check the datasheets. Then come here for more experienced help.
Thanks to all for your assistance.

Dwight
These PICS are like intricate puzzles just waiting for one to discover their secrets and MASTER their capabilities.

[languer]

I believe rmteo already answered the original question (use of auto-baud feature). I thought I add the Microchip AppNote which describes how to "auto-calibrate" the internal oscillator.

http://ww1.microchip.com/downloads/e...tes/00244A.pdf

[circuitpro]

As long as I've been working with PICs and PBP, I am still intimidated when I see an ASSY program, and I am going to read this ApNote fully today. Do you incorporate this routine into your PBP program to run at some predefined interval? Another thing that concerns me is that it appears to use Timer1, and I want to use DT_INTs, including the elapsed timer routine. Will this clobber that? Can you tell me or show me how you incorporate this into a PBP program? (I am doing what Charles is, and need an accurate INTRC for a high speed uart.)

Thanks for any further enlightenment for getting this routine flying.

(I hope to use this with an 18F2420).

[Charles Linquis]

If you are building a PIC network, and need some pointers, I can give you some if you wish.

Unless you get really creative, you have to turn off interrupts while you send/receive in software.