Don't touch that last location!  What is there is a movlw instruction along
with the factory calibrated oscal value.  When the chip is powered up it
resets at the top of memory, does the mov to load the value into w and then
the program counter rolls over to 0.  If you want to use the calibration
then your first command (at org 0) will be movf oscal.

Lots of programers will clear memory before writing a chip, or write nop to
ALL 'unused' program ROM, so it is good (safe) practice to read the chip,
and manually write the movlw xx back to the correct location when programing
it.

Bye.

-----Original Message-----
From: Drew Vassallo [mailto:snurple@HOTMAIL.COM]
Sent: Monday, 19 November 2001 14:02
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: OSCCAL for 12C671


I haven't used this chip yet, but I am planning on using it for an upcoming
project.  I notice that in the datasheet there is a section that explains
the INTRC feature.

From what I can gather, I am supposed to issue a CALL to the last program
memory location (0x3FF) in order to retrieve the predetermined calibration
value, then load this into the OSCCAL register.  Do I have to do this right
at the start of the program as an initialization?  Or is the "nominal" 4 MHz
frequency ordinarily acceptable?  I'm planning on doing bit-banged I2C
comms.

The datasheet also states that before erasing the chip, this value should be
"saved".  My question is: how do I know what this value is, and how do I
"save" it?

Thanks,

--Andrew

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