OSCCAL and compiler version 2.706

Doug · Guest

Hi all, I am working on a project which uses a 12c672 chip. I have version 2.706 of the CCS compiler. Digging through the archives of this board I discovered that a problem with OSCCAL was fixed in 2.708 of the compiler. Does anyone know what the fix was? My assembly output of the call to the OSCCAL calibration looks likes this after I compile the code:

Felix Althaus · Posted: Tue Feb 17, 2004 6:36 am

Hello

I don't remeber how much ROM the 672 has, but if it's 2048 words, your code seems to be correct (if there is a 'RETLW XX' instruction at address 0x7FF).

Felix

Doug · Guest

Ok, good

. Its a 2K rom, I just wasn't sure if there was a change made which affected the loading of the OSCCAL register.

Thanks,
Doug

Felix Althaus · Posted: Tue Feb 17, 2004 10:21 am

Hello Doug

I'm very sorry but I think I have overlooked something:

Your compiler stores the osccal value in the register 0x05 but that's the GPIO. Can you have a look at the PIC12c672 output of the picchips program? What does it say about the osccal register location?
If the fault is there, perhaps you can correct it with the device table editor. If you don't have one you can use this code (as I do):

#byte OSCCAL = 0x8F

// somewhere at the beginning of main():
OSCCAL = YOUR_VALUE;

The compiler should handle the bank switching automatically.

Felix

Doug · Guest

Ahhh... yes, the data sheet says the OSCCAL value is at 8F. I thought it was kind of strange that the value got writen to 05 but I figured it was due to bank selection.

So if I program multiple chips can I do my own routine at the beginning like:

Felix Althaus · Posted: Tue Feb 17, 2004 1:19 pm

Yes that's possible, but I don't know if the compiler accepts a #byte-definition within assembly code. Perhaps you have to define OSCCAL with:

#define OSCCAL 0x8F

Perhaps you also have to switch to the correct bank (and back) before moving the return value to OSCCAL.

Felix

Doug · Guest

Ok, according to the data sheet I only have to set bit 5 of register 3 (status register) to switch banks. But what does putting 0x07 into PCLATH (0A) before the call to 0x7FF do? Is this another form of bank switching? I'm confused about the use of banks.

Thanks,
Doug

Felix Althaus · Posted: Tue Feb 17, 2004 3:15 pm

Hi

The 0x07 into PCLATH is the "page switch" so the PIC can access the upper program memory pages (in this case the highest one where the retlw XX lies).

Have a look at the datasheet.

Felix

Doug · Guest

Thanks Felix!

I didn't know "page switch" and "bank select" were two different things. I need to learn more. Confused

I'll look into it.

Doug · Guest

Ok I think I have it now.....

Here's what I did: