Thanks for the response Lyle, Mike. In your opinion will a 'correctly'
calibrated 12F675 communicate serially alright? Surely a 4MHz clock driven
device is capable of that sort of timing?

-----Original Message-----
From: Mike Harrison [mailto:mike@WHITEWING.CO.UK]
Sent: Friday, May 02, 2003 13:03
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: 12F675, internal oscillator fine tuning ?


On Fri, 2 May 2003 12:00:28 +0200, you wrote:

>Jason Dini wrote:
>
>>Anybody know why a value has to be retrieved from this position (3FFh)
>>rather than just enter it yourself. Is this value something that varies
from
>>batch to batch?
Yes - that's the whole point of the calibration system.
Production variations inevitably result in differences between parts - this=

is inherent in all
semiconductor manufacturing.
By doing a cal at a late stage of factory testing, it allows the production=

variations to be 'ironed
out', giving reasonable accuracy with high yeild (i.e. low cost).

>
>> What also worries me is an erase of the chip loses this
>>important value.
So when you get a new chip, the first thing you do is read out the cal valu=
e
and write it on the
chip.
For in-system reprogramming of flash parts, you make sure that your system
reads out the value
before erasing,.

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