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 <[email protected]> >>> To: Discussion of precise time and frequency measurement >>> <[email protected]> >>> 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: [email protected] [mailto:[email protected]] On >>> Behalf Of Stanley Reynolds >>> Sent: Friday, July 02, 2010 3:41 PM >>> To: [email protected] >>> 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 >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
