The internal RC osc is not quite accurate enough for reliable RS232 =
comms.=20

There is one solution which can be applicable to some applications, =
however. If you can arrange to
always receive a specific character on startup (ideally 00),  you can =
measure the length of this
incoming data and use this to calibrate the timing of your RS232 code. =
This calibration will give
sufficient accuracy as long as there are no significant changes in supply=
 voltage or temperature
since calibrating.

=46or PIC-to-PIC type comms, a pulse-width encoding system, which is less=
 sensitive to timing errors,
will work fine with INTRC oscs.=20



On Fri, 2 May 2003 14:18:17 +0200, you wrote:

>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 =
value
>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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