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'[PIC]: I2C Isolation'
2000\11\07@123759 by Richard Crossley

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Does anyone have any examples or information on optically isolating a
_multi-master_ I2C bus that they could share ?

Thanks,

Richard

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2000\11\07@234814 by Alok Dubey (OCS-BLRRO-AVS)

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use a simple optocoupler..which supports the speed..
Alok

> -----Original Message-----
> From: Richard Crossley [SMTP:.....rcrossleyKILLspamspam@spam@DIGITIMER.COM]
> Sent: Tuesday, November 07, 2000 11:03 PM
> To:   PICLISTspamKILLspamMITVMA.MIT.EDU
> Subject:      [PIC]: I2C Isolation
>
> Does anyone have any examples or information on optically isolating a
> _multi-master_ I2C bus that they could share ?
>
> Thanks,
>
> Richard
>
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2000\11\08@003204 by Robert Rolf

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Yes, but the trick is to make it _bidirectional_ so you can see the
ACK bit from the slave. NOT so simple...(but prove me wrong. I figure
on two optos per line (in and out) and some logic to allow you
to drive the bus without getting a latchup (I.E. not seeing your
assertion, yet allowing you to see others to sense collisions).


"Alok Dubey (OCS-BLRRO-AVS)" wrote:
>
> use a simple optocoupler..which supports the speed..
> Alok
>
> > {Original Message removed}

2000\11\08@022028 by Nigel Goodwin

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In message <3A08E44E.97D38DA3spamspam_OUTUAlberta.ca>, Robert Rolf
<@spam@Robert.RolfKILLspamspamUALBERTA.CA> writes
>Yes, but the trick is to make it _bidirectional_ so you can see the
>ACK bit from the slave. NOT so simple...(but prove me wrong. I figure
>on two optos per line (in and out) and some logic to allow you
>to drive the bus without getting a latchup (I.E. not seeing your
>assertion, yet allowing you to see others to sense collisions).

You require three opto-couplers, I saw a circuit once on the web for an
opto-coupled PC I2C interface.
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2000\11\08@031852 by Russell McMahon

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I have several circuits somewhere for standard I2C optical isolation that I
could dig out if nobody else has anything.
As these allow bidirectional signalling cross the optical interface they
should be suitable for multimaster as well.


     Russell McMahon
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{Original Message removed}

2000\11\08@040103 by Michael Rigby-Jones

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> -----Original Message-----
> From: Nigel Goodwin [SMTP:RemoveMEnigelgTakeThisOuTspamLPILSLEY.CO.UK]
> Sent: Wednesday, November 08, 2000 7:21 AM
> To:   spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU
> Subject:      Re: [PIC]: I2C Isolation
>
> In message <TakeThisOuT3A08E44E.97D38DA3EraseMEspamspam_OUTUAlberta.ca>, Robert Rolf
> <RemoveMERobert.RolfspamTakeThisOuTUALBERTA.CA> writes
> >Yes, but the trick is to make it _bidirectional_ so you can see the
> >ACK bit from the slave. NOT so simple...(but prove me wrong. I figure
> >on two optos per line (in and out) and some logic to allow you
> >to drive the bus without getting a latchup (I.E. not seeing your
> >assertion, yet allowing you to see others to sense collisions).
>
> You require three opto-couplers, I saw a circuit once on the web for an
> opto-coupled PC I2C interface.
>
Four optos if you need to read back the clock line (i.e. talking from a PC
to a PIC that uses clock stretching).  I have built an opto-isolated
interface and it works well.  Only disadvantage is that you obvioudly need
two supplies.  I used a splitter on the PC's keyboard cable, but you could
also use e.g. the game port.

Take a look at : http://www.hut.fi/~iisakkil/i2c_adap.gif

Regards

Mike

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2000\11\08@041612 by Alok Dubey (OCS-BLRRO-AVS)

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not only the ACK bit , also the errors/collisons or  "bus contention " for
multimaster are monitored on the SCL.. and the SDA is also checked for data
corruption ..so everyting has to be Bi. .

frankly im badly out of touch of this stuff.. last time i worked was 2 yrs
ago..and have moved out of embedded systems completely..

u l need to access a latch , to syncro it with some clock, either the SCL..
for that u will have to seperate the SCLs coming form both inside and
outside ...
there is some other way ,.. i cant rememebr exactly.. when u use the I2C
isr.. just place a set of signal lines , mebbe some addr-bus lines high at
the end of your routine, capture this using some Gates.. and use this to
synchro the latch..im not sure if using 3 optocouplers wrks.. it might be
"for the given scenario" ..not a general soln.


Alok


{Original Message removed}

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