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'RS232 possible using internal oscillator?'
1999\08\12@235514 by Bruce Cannon

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Hello:
Reading the specs for 12Cxx, looks like calibrated osc value can vary nearly
+-500kHz.  Has anyone used these parts (with internal osc) for serial comm,
and if so, how?

Bruce Cannon
Style Management Systems
1228 Ceres ST Crockett CA 94525
(510) 787-6870
http://www.jps.net/bcannon

Remember: electronics is changing your world...for good!

1999\08\13@001631 by Tjaart van der Walt

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Bruce Cannon wrote:
>
> Hello:
> Reading the specs for 12Cxx, looks like calibrated osc value can vary nearly
> +-500kHz.  Has anyone used these parts (with internal osc) for serial comm,
> and if so, how?

You will be, as long as you re-synch on every start bit on RX.
On TX, you can also get away with it if your inter-character
spacing is long enough.

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1999\08\13@004403 by Dan Creagan

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There are several examples of using 2400 with the 12CXX series on the web -
try Dennis Clark's page for a start

http://www.verinet.com/~dlc/projects/botproj.htm#serserv.

I have used it with serial LCDs at 9600 - for debug, but the strings have
been very short.

Dan

{Original Message removed}

1999\08\13@011340 by David Duffy

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<x-flowed>Bruce Cannon wrote:
> Reading the specs for 12Cxx, looks like calibrated osc value can vary nearly
> +-500kHz.  Has anyone used these parts (with internal osc) for serial comm,
> and if so, how?

I use the 12C509 @ 2400 baud & the 12C672 @ 9600 baud with no problems.
The graph for '672 shows 50-100KHz variation near 25 Celcius not 500KHz.
With a regulated 5V supply there should be no problems. Even 100KHz off
would be about 2.5% error - still only 25% over a 8N1 byte length. If you
sample
right in the middle of each bit that still leaves a good margin. Our serial
routines
are bit-bashed and I used the simulator to tweak the basic bit timing.
Regards...
___________________________________
David Duffy               Audio Visual Devices
Ph: +61 7 38210362   Fax +61 7 38210281
.....AVDKILLspamspam@spam@uq.net.au  Unit 8, 9-11 Trade Street
Cleveland, Qld, 4163, Australia.
___________________________________

</x-flowed>

1999\08\13@082812 by Jack Shidemantle

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I am using the 12C509 with internal osc. and bit banging RS232 at 9600 baud
(8N1). It works fine as long as you plug in correct osc. calibration.  It
is in one of our products and have seen no problems yet from about 100
units.



                   Bruce Cannon
                   <bcannon@JPS.N        To:     PICLISTspamKILLspamMITVMA.MIT.EDU
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                   08/12/99 11:48
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Hello:
Reading the specs for 12Cxx, looks like calibrated osc value can vary
nearly
+-500kHz.  Has anyone used these parts (with internal osc) for serial comm,
and if so, how?

Bruce Cannon
Style Management Systems
1228 Ceres ST Crockett CA 94525
(510) 787-6870
http://www.jps.net/bcannon

Remember: electronics is changing your world...for good!

1999\08\13@131905 by Bruce Cannon

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Hello all:

I never do a good enough job of explaining myself to start with when I ask
questions on this list!  Sorry.  I should have mentioned that I've already
done serial comm with the parts, from 2400 to 9600, in my shop.  I noticed
some occasional comm problems and dug deeper into the data sheets, where I
saw that (in the 508A-519 parts at least), the range for the calibrated osc
varies from 3.55 to 4.31MHz.  Which I think is another way of saying you
could be 450kHz off.

And so while it's clear you could tweak by trial and error at both ends to
get reliable transmissions based on specific parts for playing around or
small volume, it seems it might be tougher to mass produce a cheap high
volume product which talks to a PC at, say, 4800bps.  (The PC isn't going to
tweak, it's just going to choke).  What I really meant to ask about was
about anyone's experience with a high volume design which works.

Thanks for the input,

Bruce Cannon
Style Management Systems
1228 Ceres ST Crockett CA 94525
(510) 787-6870
http://www.jps.net/bcannon

Remember: electronics is changing your world...for good!


{Quote hidden}

1999\08\13@133330 by Dave VanHorn

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> And so while it's clear you could tweak by trial and error at both ends to
> get reliable transmissions based on specific parts for playing around or
> small volume, it seems it might be tougher to mass produce a cheap high
> volume product which talks to a PC at, say, 4800bps.  (The PC isn't going
to
> tweak, it's just going to choke).  What I really meant to ask about was
> about anyone's experience with a high volume design which works.


You could, however,  tweak on the PIC end.  The bit time is going to be the
same as the narrowest width observed during a char. If you can get the PC to
send you a couple of chars, you could sniff out the proper speed values.
You'd need to measure and find the width of the bit-time from looking at
bytes with a timer (or timing loop)
It's workable, provided the host sends reasonable chars, not nulls.
Actually, $FF would be easy, since all you'd ever see would be the start
bit, or maybe $FE so you can check the last zero and fine-tune.

1999\08\13@135041 by Jack Shidemantle

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By high volume you probably mean thousands. For me it's hundreds. Anyway we
are shipping units in hundreds using the internal osc of a 12C509 for short
strings of RS232 at 9600 baud. I will qualify this and say if I had it to
do all over again I would add a $0.40 crystal and two $0.05 caps to
guarantee a more accurate osc frequency. We do not do any tweaking with the
present OTP's.  Just be sure you don't overwrite the built in osc cal
values. (Maybe you can't overwrite them I don't remember now)



                   Bruce Cannon
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                   08/13/99 01:11
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Hello all:

I never do a good enough job of explaining myself to start with when I ask
questions on this list!  Sorry.  I should have mentioned that I've already
done serial comm with the parts, from 2400 to 9600, in my shop.  I noticed
some occasional comm problems and dug deeper into the data sheets, where I
saw that (in the 508A-519 parts at least), the range for the calibrated osc
varies from 3.55 to 4.31MHz.  Which I think is another way of saying you
could be 450kHz off.

And so while it's clear you could tweak by trial and error at both ends to
get reliable transmissions based on specific parts for playing around or
small volume, it seems it might be tougher to mass produce a cheap high
volume product which talks to a PC at, say, 4800bps.  (The PC isn't going
to
tweak, it's just going to choke).  What I really meant to ask about was
about anyone's experience with a high volume design which works.

Thanks for the input,

Bruce Cannon
Style Management Systems
1228 Ceres ST Crockett CA 94525
(510) 787-6870
http://www.jps.net/bcannon

Remember: electronics is changing your world...for good!


{Quote hidden}

1999\08\13@145124 by Barry King

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>What I really meant to ask about was
> about anyone's experience with a high volume design which works.

If I had to do it, I would do "autobaud".  That requires the PC to
send at least one known character to the device to measure the bit
time.  An odd-code ASCII char works best, since the start bit is
always zero, you can time the start bit.  Hayes modems, of course,
use 0x41h ("A" of the first "AT command ) to autobaud.

Measure a bit time in cycles and remember it.  Then the
oscillator frequency doesn't matter as long as its stable and
reasonably fast.

If you have to be unidirectional, of course, this won't work.  But if
you can, you get auto baudrate setting in the bargain.

Barry.
------------
Barry King, KA1NLH
Engineering Manager
NRG Systems "Measuring the Wind's Energy"
Hinesburg, Vermont, USA
http://www.nrgsystems.com

1999\08\13@205657 by J Nagy

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Bruce Cannon wrote:

>Hello:
>Reading the specs for 12Cxx, looks like calibrated osc value can vary nearly
>+-500kHz.  Has anyone used these parts (with internal osc) for serial comm,
>and if so, how?
>

       Certainly! We've had good results using '508 devices with 9600 baud
comms that rely on the internal oscillator for timing. Our measurements
show that it's pretty good at normal temps and ~5V Vdd.
       To reduce timing errors though, keep transmissions short (stick to
8N1, and preferrably 8N2 if you can afford the time). With 8 data and 1
start and even 5% timing error, you're only looking at 45% total error. By
receiving or sending only a few bytes at a time, the receivers have a
chance to reset and errors don't accumulate. A 256bit block would likely be
impossible to send reliably.


       Jim Nagy
       Elm Electronics
 ICs for Experimenters
http://www.elmelectronics.com/

1999\08\13@214727 by Jose Souto

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Hello,
I'm developing a MIDI receiver at 32150 bps with a 12ce518
and it working fine with several MIDI transmiters. It's
currently being tested in USA. I can't report any error
since I'm not doing the tests but the testers plays songs
with keybords and they certainly can hear the errors...

It's working, if it may help,

   J Souto
   @spam@soutoKILLspamspamcryogen.com

1999\08\14@011451 by Jim Robertson

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At 20:48 12/08/99 -0700, you wrote:

You have had some good replies so far. One point I would make is that there
are
two different internal OSCCAL schemes used by PICs and one gives much better
resolution than the other.

Now this is from memory so please check. The 12C508/9 has the poorer scheme.
The 12C508A and 509A, 12CE518 and 519, 12C67x have the better scheme. I am not
sure about the 16C505.

I think it is reasonable to surmise the parts with greater OSCCAL resolution
are more accurate than those with the poorer scheme. Maybe this is worth
further
comment from piclisters?


Jim



{Quote hidden}

Regards,

Jim Robertson
NEWFOUND ELECTRONICS
________________________________________
Email: KILLspamnewfoundKILLspamspampipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.
________________________________________

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