Well, since you mentioned that your UART is not available, using
SPI allows you to make use of hardware in the PIC to handle the
communication. It would be much easier if you aren't having to do
a nasty hack in software. Make use of the peripherals if possible.

Andrew

On Sun, May 09, 2004 at 04:24:18PM -0400, Denny Esterline wrote:
> 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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