[time-nuts] Pictic II mods
Bob Camp
lists at rtty.us
Sat Jul 3 00:39:11 UTC 2010
Hi
The gotcha with the tune register is that it's not much help for those without a PIC programmer...
Bob
On Jul 2, 2010, at 8:15 PM, Richard H McCorkle wrote:
> Bob,
> Another option with the 16F688 is to "tweak" the internal oscillator
> rate slightly to give the proper baud rate. The code includes the
> following two lines (normally commented out) to do this.
>
> ; movlw 0x00 ;put the cal value in OSCTUNE
> ; movwf OSCTUNE ;to calibrate oscillator
>
>> From the Spec Sheet:
>
> 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 ‘0’. The value is a 5-bit two’s 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 = Maximum frequency
> 00001 = Increasing Frequency
> 00000 = Oscillator module is running at the calibrated frequency.
> 11111 = Decreasing Frequency
> 10000 = 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 two 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, external 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 febo.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 accurate,
>>> 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] On
>>> 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 (51. for
>>> 8
>>> MHz int, BRGH=1)
>>> 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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>
>
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