If you wish to avoid the CS lines,
Imbed the address of the target in the SPI comm. protocol.

  *
  |  __O    Thomas C. Sefranek  WA1RHP@ARRL.NET
  |_-\<,_   Amateur Radio Operator: WA1RHP
  (*)/ (*)  Bicycle mobile on 145.41 MHz PL 74.4

ARRL Instructor, Technical Specialist, VE Contact.
http://hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Denny Esterline
> Sent: Sunday, May 09, 2004 4:24 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE:] Isolated PIC-PIC communication
>
>
> Wouldn't that require an additional line (CS)? Shared Din, Dout, and Clk
> plus a CS per node. Instead of Shared Din and Dout with a Clk per node?
>
> I cant really see the improvement, but maybe I'm missing something?
>
> -Denny
>
>
>
> > Opto-Isolated SPI.
> >
> >   *
> >   |  __O    Thomas C. Sefranek  WA1RHP@ARRL.NET
> >   |_-\<,_   Amateur Radio Operator: WA1RHP
> >   (*)/ (*)  Bicycle mobile on 145.41 MHz PL 74.4
> >
> > >
> > > I'm looking at a project that will have several (4-8) PICs in the
> circuit.
> > > They need low bandwidth (~100 bytes/sec) communication between each
> node
> > > and the main controller. The problem is they need galvanic
> > > isolation, there
> > > could be a couple hundred volts difference between them. Main PIC will
> > > probably be a 16F877 handling front panel details (character LCD and
> > > buttons) as well as connection to host PC, nodes will probably be
> 12F675s
> > > or 16F676s.
> > >
> > > They'll be within a few inches of each other, and there shouldn't be
> any
> > > significant 'noise' to overcome. The USART on the main controller is
> > > already committed and I have to avoid using the interrupts on
> the nodes
> (I
> > > already have several processes happening there) And I'd like to avoid
> > > crystals/resonators on the nodes if possible. (cost, complexity,
> > > not needed
> > > for main task anyway) So I think typical RS232 is out.
> > >
> > > I was thinking of perhaps a clocked serial similar to a shift
> > > register. One
> > > pin on the central controller for data in, one for data out, and one
> per
> > > node for clock.
> > >
> > > Doable, but I was hoping for a more elegant solution. Any suggestions?
> > >
> > > Thanks,
> > > -Denny
> > >
> > > --
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> > >
> > >
> >
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