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The HFINTOSC is factory calibrated but can be adjusted in software
by writing to the OSCTUNE register. The default value of the OSCTUNE
register is =910=92. The value is a 5-bit two=92s complement number. When
the OSCTUNE register is modified, the HFINTOSC frequency will begin
shifting to the new frequency. Code execution continues during this
shift.

bit 4-0 TUN<4:0>: Frequency Tuning bits

01111 =3D Maximum frequency
00001 =3D Increasing Frequency
00000 =3D Oscillator module is running at the calibrated frequency.
11111 =3D Decreasing Frequency
10000 =3D Minimum frequency

Richard


> Hi
>
> Yup, and as you go to higher baud rates the +/- one makes for a bigger =
"hop" in the
> baud rate.
>
> One cute way to attack the problem:
>
> Set the baud rate so it *should* be fast
> Set the PIC transmitter to send two stop bits (or marking parity and tw=
o stop bits
> if you can).
> Set the PC receiver to look for one stop bit and no parity.
>
> Net result is that you can tolerate a much higher baud rate error in a =
"transmit
> mostly" application like this one.
>
> Bob
>
>
> On Jul 2, 2010, at 5:44 PM, Stanley Reynolds wrote:
>
>> yes, internal clock, may need to tune the osc or try +- one number, ex=
ternal osc
>> pins are in use.
>>
>> Stanley
>>
>>
>>
>> ----- Original Message ----
>> From: Bob Camp <lists at rtty.us>
>> To: Discussion of precise time and frequency measurement <time-nuts at fe=
bo.com>
>> Sent: Fri, July 2, 2010 4:11:11 PM
>> Subject: Re: [time-nuts] Pictic II mods
>>
>> Hi
>>
>> I believe he's using the internal clock on the PIC. It's not super acc=
urate,
>> so running a lot of data can be an issue.
>>
>> Bob
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] O=
n
>> Behalf Of Stanley Reynolds
>> Sent: Friday, July 02, 2010 3:41 PM
>> To: time-nuts at febo.com
>> Subject: [time-nuts] Pictic II mods
>>
>> Looking at Richard's code in PICTICII.ASM :
>>
>>    bsf     TXSTA,BRGH            ;set USART hi speed mode
>>    movlw D'51'                         ;set async rate at 9600 baud (5=
1. for
>> 8
>> MHz int, BRGH=3D1)
>>    movwf SPBRG
>>
>> Then '25' would be 19,200 baud
>> and '12' would be 38,400 baud
>>
>> Need to test this but could be a way to get more data out.
>>
>> Stanley
>>
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>
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