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'[PICLIST] 16f628 and i2c; 16f628 with internal osc'
2002\07\03@142248 by Giorgio De Nunzio

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Hi all!
I am building up some code on a 16f628 for i2c communication.
I have found a lot of stuff about software i2c (on 84 and so on), but
nothing exploiting the internal usart. Is there some code available? Asm, if
possible.

I am curious about the use of the 628 with no xtal: what about serial
communication speed when no xtal is used? At what baud rate can the pic
still work? I am going to do some test this evening on the precision of the
internal pwm with no xtal.

Thanks!
Ciao
Giorgio

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2002\07\03@143338 by Dinho AeS

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Giorgio,

What do you want to use? I2C or USART?

In order to use I2C you will use SPI Pins and Registers.

Dinho

{Original Message removed}

2002\07\03@144749 by Harold M Hallikainen

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On Wed, 3 Jul 2002 20:20:57 +0200 Giorgio De Nunzio
<spam_OUTgiorgio.denunzioTakeThisOuTspamUNILE.IT> writes:
> Hi all!
> I am building up some code on a 16f628 for i2c communication.
> I have found a lot of stuff about software i2c (on 84 and so on),
> but
> nothing exploiting the internal usart. Is there some code available?
> Asm, if
> possible.
>
> I am curious about the use of the 628 with no xtal: what about
> serial
> communication speed when no xtal is used? At what baud rate can the
> pic
> still work? I am going to do some test this evening on the precision
> of the
> internal pwm with no xtal.

       In my opinion, relying on an RC oscillator as the BRG for a UART is
asking for trouble. A ceramic resonator has enough accuracy to handle a
UART, though. Resonators with built-in capacitors are cheap and smaller
than crystals.

Harold



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2002\07\03@152342 by Gabriel Caffese

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I´ve been using the 16F627/28´s UART with the internal oscilator in several
projects, up to 19200bauds, and
have NEVER had a problem. If problems would have appeard, I would prefer to
add a checksum or any kind of data
control to it, rather than put a cristal o resonator. Not only for the cost.
Just simplicity.

       Gabriel.-


-----Mensaje original-----
De: pic microcontroller discussion list
[.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU]En nombre de Giorgio De Nunzio
Enviado el: Miércoles, 03 de Julio de 2002 15:21
Para: PICLISTspamKILLspamMITVMA.MIT.EDU
Asunto: 16f628 and i2c; 16f628 with internal osc


Hi all!
I am building up some code on a 16f628 for i2c communication.
I have found a lot of stuff about software i2c (on 84 and so on), but
nothing exploiting the internal usart. Is there some code available? Asm, if
possible.

I am curious about the use of the 628 with no xtal: what about serial
communication speed when no xtal is used? At what baud rate can the pic
still work? I am going to do some test this evening on the precision of the
internal pwm with no xtal.

Thanks!
Ciao
Giorgio

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2002\07\03@154130 by Spehro Pefhany

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At 04:31 PM 7/3/02 -0300, you wrote:
>I´ve been using the 16F627/28´s UART with the internal oscilator in several
>projects, up to 19200bauds, and
>have NEVER had a problem. If problems would have appeard, I would prefer to
>add a checksum or any kind of data
>control to it, rather than put a cristal o resonator. Not only for the cost.
>Just simplicity.

I guess you don't really care if the communications work or not. Wouldn't it
be even simpler just to leave them out entirely?

Best regards,

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2002\07\03@154532 by uter van ooijen & floortje hanneman

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> I´ve been using the 16F627/28´s UART with the internal oscilator in
several
> projects, up to 19200bauds, and
> have NEVER had a problem. If problems would have appeard, I would prefer
to
> add a checksum or any kind of data
> control to it, rather than put a cristal o resonator. Not only for the
cost.
> Just simplicity.

That fact that it often works is no proof that it is a good idea. Did you
try (combinations of) the extremes of Vcc and temperature, plus a few other
parameters, and ageing?

And when it fails it will probably fail in a repeatable manner, so a
checksum make sure that the problem is noted, but retransmission will not
solve the problem.

Wouter van Ooijen
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2002\07\03@164311 by Gabriel Caffese

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You may be right, but adding a checksum in CCS´s C compiler is just a few
lines.
I insist, it´s simpler to add a checksum than adding a cristal or resonator.

       Gabriel.-


-----Mensaje original-----
De: pic microcontroller discussion list
[EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU]En nombre de wouter van ooijen & floortje
hanneman
Enviado el: Miércoles, 03 de Julio de 2002 04:20
Para: PICLISTspamspam_OUTMITVMA.MIT.EDU
Asunto: Re: 16f628 and i2c; 16f628 with internal osc


> I´ve been using the 16F627/28´s UART with the internal oscilator in
several
> projects, up to 19200bauds, and
> have NEVER had a problem. If problems would have appeard, I would prefer
to
> add a checksum or any kind of data
> control to it, rather than put a cristal o resonator. Not only for the
cost.
> Just simplicity.

That fact that it often works is no proof that it is a good idea. Did you
try (combinations of) the extremes of Vcc and temperature, plus a few other
parameters, and ageing?

And when it fails it will probably fail in a repeatable manner, so a
checksum make sure that the problem is noted, but retransmission will not
solve the problem.

Wouter van Ooijen
--
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2002\07\03@164855 by Harold M Hallikainen

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On Wed, 3 Jul 2002 17:50:23 -0300 Gabriel Caffese
<@spam@gabrielsdiKILLspamspamIMPSAT1.COM.AR> writes:
> You may be right, but adding a checksum in CCS4s C compiler is just a
> few
> lines.
> I insist, it4s simpler to add a checksum than adding a cristal or
> resonator.
>

       And when temperature forces the transmit and receive frequencies far
enough apart that checksum fails, you just keep detecting the failure of
acknowledgement and retransmitting until the temperatures get back in
range (perhaps the next day when the sun comes up).

Harold


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2002\07\03@165630 by Brandon Stewart

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The cost of A crystal and 2 caps is pocket change.  A checksum will not keep
you accurate, it will just tell you that your NOT accurate.
 --> If one is only concerned with simplicity- then just design things in
your head and never put them into practice, because that is where nothing is
ever simple!  Use a Xtal or resonator.... trust me.




{Original Message removed}

2002\07\03@195908 by Harold Hallikainen

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Another possibility here is to use a bit banged self clocking code. Slow variations in clock frequency would then not matter.

Harold




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2002\07\03@200738 by Gabriel Caffese

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Harold,

       Would you explain me a bit more ?
               Thanks.-


-----Mensaje original-----
De: pic microcontroller discussion list
[KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU]En nombre de Harold Hallikainen
Enviado el: Miércoles, 03 de Julio de 2002 20:57
Para: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU
Asunto: Re: 16f628 and i2c; 16f628 with internal osc


Another possibility here is to use a bit banged self clocking code. Slow
variations in clock frequency would then not matter.

Harold




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2002\07\03@211950 by Bob Ammerman

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This is doable at low baud rates by dithering the baud rate divisor until
you get a good checksum. In some limited problem domains it even makes
sense.

You can also use techniques like measuring the duration of a leadin
character on a poll to determine the correct  BRG value. This latter
technique is, IMO, a better idea than just tweaking the divisor until it
works.

At higher baud rates these tricks won't work because changing the BRG
divisor by just one count will result in a very large percentage change in
the baud rate.

Bob Ammerman
RAm Systems

{Original Message removed}

2002\07\04@062941 by ISO-8859-1?Q?Ruben_J=F6nsson?=

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> Hi,
>
>     It you use a bitbang software UART you can measure the start bit
> duration and use it as a reference for other bit's position. That way
> you can compensate for variations on the clock caused by temperature
> changes. The temperature changes are usually not too fast. With the
> hardware uart you better use a resonator...

You can only measure the length of the startbit if you know
that the first bit (D0) in the transmitted data is a one, which
has the opposite level of the startbit.

Sending the value 0 with 8 databits, no parity would give you a
single pulse that is 9 bits long.

Ruben


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2002\07\04@105334 by gaston gagnon

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Gabriel Caffese a icrit :

> Harold,
>         Would you explain me a bit more ?
>                 Thanks.-

Gabriel,
Alexander Guimaraes gives a pretty good description of a method in two
previous messages. You may want to read them again :

Objet:   Re: [PIC]: 16F628 internal oscillator
Date:    Sat, 29 Jun 2002 17:48:17 -0300
De:        Alexandre Guimarces <RemoveMEalexgspamTakeThisOuTMS.MICROLINK.COM.BR>

Objet:    [PIC]: Re: 16f628 and i2c; 16f628 with internal osc
Date:     Wed, 3 Jul 2002 17:56:59 -0300
De:        Alexandre Guimarces <alexgEraseMEspam.....MS.MICROLINK.COM.BR>


> de Harold Hallikainen
> Enviado el: Miircoles, 03 de Julio de 2002 20:57
>
> Another possibility here is to use a bit banged self clocking code. Slow
> variations in clock frequency would then not matter.
>
> Harold
>

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2002\07\04@131309 by Gabriel Caffese

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Thank you. I´m gonna sit and read them.
  Gabriel.-

-----Mensaje original-----
De: pic microcontroller discussion list
[RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU]En nombre de gaston gagnon
Enviado el: Jueves, 04 de Julio de 2002 01:00
Para: RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU
Asunto: Re: 16f628 and i2c; 16f628 with internal osc


Gabriel Caffese a icrit :

> Harold,
>         Would you explain me a bit more ?
>                 Thanks.-

Gabriel,
Alexander Guimaraes gives a pretty good description of a method in two
previous messages. You may want to read them again :

Objet:   Re: [PIC]: 16F628 internal oscillator
Date:    Sat, 29 Jun 2002 17:48:17 -0300
De:        Alexandre Guimarces <RemoveMEalexgTakeThisOuTspamspamMS.MICROLINK.COM.BR>

Objet:    [PIC]: Re: 16f628 and i2c; 16f628 with internal osc
Date:     Wed, 3 Jul 2002 17:56:59 -0300
De:        Alexandre Guimarces <EraseMEalexgspamspamspamBeGoneMS.MICROLINK.COM.BR>


> de Harold Hallikainen
> Enviado el: Miircoles, 03 de Julio de 2002 20:57
>
> Another possibility here is to use a bit banged self clocking code. Slow
> variations in clock frequency would then not matter.
>
> Harold
>

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2002\07\05@130914 by Harold M Hallikainen

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On Wed, 3 Jul 2002 21:15:59 -0300 Gabriel Caffese
<spamBeGonegabrielsdiSTOPspamspamEraseMEIMPSAT1.COM.AR> writes:
> Harold,
>
>         Would you explain me a bit more ?
>                 Thanks.-
>

       The word escapes me right now... But there's the self clocking code
sometimes used on disk drives. There's the self clocking code used in bar
codes. About 25 years ago I did a self clocking code for use on a digital
tape drive (anyone remember the "Stringy Floppy?"). Here, a long time
between transitions was a binary 1, and a short time between transitions
was a binary 0. I emulated a UART, including a 1 stop bit at the end of
each byte, and a 0 start bit at the beginning of each byte. At the
beginning of the tape was a bunch of 1's that the firmware used for its
initial 1 timing. It used this to establish a threshold. A transition in
less time than the threshold would be called a zero, while a transition
in more time would be called a 1. Each zero and one was timed and used to
adjust the threshold so slow variations in tape speed were compensated
for.

Harold


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2002\07\05@132556 by Tom Messenger

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At 09:56 AM 7/5/02 -0700, you wrote:
>Harold writes:
>        The word escapes me right now... But there's the self clocking code
>sometimes used on disk drives.

Could you be thinking of 'manchester' encoding? It is one form of
self-clocking serial data transmission.  For a quick explanation, see:


http://www.thelinuxreview.com/howto/intro_to_networking/c4511.htm

Tom M.

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2002\07\05@141031 by Harold M Hallikainen

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On Fri, 5 Jul 2002 10:25:57 -0700 Tom Messenger <@spam@krist@spam@spamspam_OUTTHEGRID.NET>
writes:
> At 09:56 AM 7/5/02 -0700, you wrote:
> >Harold writes:
> >        The word escapes me right now... But there's the self
> clocking code
> >sometimes used on disk drives.
>
> Could you be thinking of 'manchester' encoding? It is one form of
> self-clocking serial data transmission.  For a quick explanation,
> see:
>
>
> http://www.thelinuxreview.com/howto/intro_to_networking/c4511.htm
>
> Tom M.
>

       Yes, that's it! Thanks Tom!

Harold



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