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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