Hi guys,

Well I've achieved my next milestone. I keyed in a few lines of code
today and had an LED flashing nicely at approximately 1Hz. However just
as I hit the program button, I realised I may have done one thing
wrong. I did not open the Program/Verify window of MPLAB. If I had, I
would have noticed that "Calibration Memory" was checked.

I know this is bad news for a JW Part - unless you record the factory
setting. Does this apply to EEPROM parts also?

The data sheet says;

"Note: Erasing the device will also erase the pre-programmed internal
calibration value for the internal oscillator. The calibration value
must be saved prior to erasing part."

However, what happens for the first write, and subsequent re-writes if
the "Calibration Memory" is selected in the Program/Verify dialogue box
is not clear.

Is it wise to erase a EEPROM part before re-writing with new code? Or
does each (used) register get cleared first prior to writing?

Sorry if this is old stuff for you guys, but I have only used OTP parts
with JW equivalents till now. I have not used a EEPROM part with
internal clock.

Also, writing to the OSCCAL register appears to be different to the
PIC12C508 and PIC12C671 parts. The data sheet now says;

bsf     STATUS, RP0     ;Bank 1
call    3FFh            ;Get the cal value
movwf   OSCCAL          ;Calibrate
bcf     STATUS, RP0     ;Bank 0

Am I mistaken, or did the PIC12C508 and PIC12C671 basically powerup at
the end of it's memory and effectively do a movlw   [calibration value]
- then your first instruction simply needed to be a MOVWF   OSCCAL -
did it not?

It's interesting that there is no Window > Calibration Data option when
I have PIC12F675 selected in MPLAB v5.70.40, however when I change to
any of the 12C series, I can open a dialogue box called "Calibration
Contants" by selecting Calibration Data from the Windows menu. How is
is possible to read (and therefore record) the factory set calibration
data for a PIC12F675 or is it simply not necessary?

Regards,

Sean Alcorn

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