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'[PIC]: Multiplex pin functions ie 16c505 osc (cal'
2000\11\01@033331 by Bob Bullock

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Lorick,

A couple of additional tips regarding the internal 4Mhz oscillator.

The operating frequency of the internal oscillator can be trimmed by writing
a calibration value into the OSCCAL register.  The oscillator is tested at the
factory and a calibration value is programmed into highest EEPROM location.
This value is NOT automatically loaded into the OSCCAL register at startup.
This last location in EEPROM 0x3FF for the 16C505 is the actual reset vector.
It contains a movlw instruction that will load the factory calibration value
into WREG, the program counter then rolls over and you are back to a 0x0000
effective reset vector.

There are two key items then.
1) To take advantage of the factory calibration, you should move WREG into
the OSCCAL
register before destroying the contents of WREG as part of your reset
vector code.

2) When you erase a windowed part, you also erase this calibration value.
When programming an erased part, you can also re-program the calibration
data value again
IF YOU KNOW WHAT IT WAS! The first thing I do when I get a shipment of
windowed
parts with an internal oscillator is read them in and write the factory set
calibration value on the part.

At 11:21 PM 10/31/2000 -0500, you wrote:
{Quote hidden}

Bob Bullock
President
Western Support Group Ltd.
spam_OUTbobbTakeThisOuTspamprostyle.com
Certified Microchip Consultants
http://www.microchip.com/10/Consult/Country/Canada/index6.htm#915-277

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2000\11\01@132505 by Lorick

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> 2) When you erase a windowed part, you also erase this calibration value.
> When programming an erased part, you can also re-program the calibration
> data value again
> IF YOU KNOW WHAT IT WAS! The first thing I do when I get a shipment of
> windowed
> parts with an internal oscillator is read them in and write the factory
set
> calibration value on the part.

I'll definitely be checking on that when I get the windowed 16c505.  Thanks
for the tips.

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