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PICList Thread
'Internal Oscillators and the PIC16C67X, confused.'
1999\02\22@144409 by c.n.morison

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Dear All,

I'm in a state of confusion over the Internal Oscillator on the
PIC16C672.  I've previously worked with PIC12's and I am now
branching into PIC16's.  I've make the PIC16 work with an external
4Mhz Xtal oscillator, but when I remove it and re-program the part
with the options set to internal oscillator, the very same program no
longer works.  Any ideas?

I also don't understand the logic in placing the OSCAL tuning
number into the end of the program memory as a RETLW
instruction.  If I have to erase the part before re-programming, then
surely I have to include this in the new program, which means
knowing what the number is.  If this is the case, why don't
Microchip just quote the number in the datasheet, and let me
program it in however I like?  What does this default tuning number
tune the clock too anyway?  Can anyone tell me what it is,
because I erased the part before I was interested in the internal
oscillator and read that bit of the datasheet?

Unless I've missed or misunderstood something, it seems totally
illogical to supply this information pre-programmed onto the part.

Can anyone alleviate this pain in my head?

Cheers.

Chris Morison
--
Research Student
Manufacturing & Mechanical Engineering
University of Birmingham
Birmingham, B15 2TT
Tel: +44 (0)121 414 4185
Fax: +44 (0)121 414 3958
e-mail: spam_OUTc.n.morisonTakeThisOuTspambham.ac.uk
web:    http://www.arcsite.de/hp/chrismorison/

1999\02\23@035737 by Dr. Imre Bartfai

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Hi,
you should keep in mind that the factory-determined OSCCAL tuning
value can be different for every PIC. Such way, one should READ and SAVE
the said value before manipulating the content of the EPROM (I wrote on
the bottom of the PIC). Then the program should contain exactly that MOVLW
statement, and then as a very 1st one MOVWF OSCCAL.  It is possible when
the programming process does not influence the very last location of the
EPROM then it remains unchanged. But, if you erase it via UV then it is
not true any more.
I hope this helps.  Imre


On Mon, 22 Feb 1999, Chris Morison wrote:

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