Nick,

Wow, thanks for the in-depth information.  I can answer some
mechanical questions, but I can't sign my name to a design;
I'm not an engineer.

Looking forward to speaking with everyone, and not throwing
out any more "stupid" questions.

Gustaf

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of James Nick Sears
> Sent: Sunday, February 15, 2004 3:13 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Greetings from a neophite PIC user.
>
>
> ----- Original Message -----
> From: "Gustaf J. Barkstrom" <gustaf.b@COX.NET>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Saturday, February 21, 2004 1:07 PM
> Subject: [OT]: Greetings from a neophite PIC user.
>
>
> > I purchased a MAX232 RS-232 controller/driver chip, and I've noticed
> > in the archives that people have had varying results with resonators
> > and xtals when controlling serial communications in software. I'm
> wondering
> > if I have to worry about clock drift between the MAX232 and a PIC, using
> > the same clock source for both (if possible), and if the MAX232 has the
> > same problems a software-based RS-232 controller has.  I'm still a
> neophite,
> > so I will try to make some sensible questions and post to the PIC:
> threads.
> >
>
> A MAX232 is just a driver.  It converts a signal from the 0-Vdd range that
> the PIC produces to the balanced +/- voltages that the RS232 spec
> requires.
> It doesn't have anything to do with the logic or timing of the
> communication
> (other than its finite rise time and fall time which limit its maximum
> usable bitrate)
>
> I haven't had any problems with serial communications using the PIC USART
> through a MAX232 or similar driver.  In the datasheet for your PIC in the
> USART section (p. 114 of the 16F87xA datasheet) you will find a table that
> shows the % timing error as a function of crystal frequency and serial
> bitrate.  Due to the fact that the baud rate is generated with integer
> divides (actually just a counter), rounding errors in the timing vary with
> bitrate.  As long as you pick a oscillator/bitrate combination that has a
> low error you should be fine.  Note that this is one reason that
> you can get
> off the shelf crystals at non round number frequencies, such as
> 3.6864 MHz,
> which divides evenly to many common bitrates for zero error (more
> precisely,
> zero division error - there will still be error from crystal
> drift, etc. but
> for RS232 bitrates and any decent crystal oscillator circuit this
> shouldn't
> cause you any problems)
>
> > Anyway, this looks like a very active group, and I'm glad to be with
> others
> > interested (and moreover knowledgable) in the electronics world.
> >
>
> It is a fantastic resource.  I'm sure you'll find a lot of useful
> information here and your mechanical knowledge will surely come
> in handy to
> the many of the rest of us on the list.
>
> Nick
>
> > Gustaf
> >
> > --
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