> I would like to have a hierarchical computing system in the robot, which
I
> have planned out as follows:
> 1. Main processor hands out simple instruction bytes to low-end
> subprocessors (I2C bus? If so, what would you recommend for me to read
so as
> to learn about it?)

Look around at the Microchip app notes.  I vaguely remember one of them
was an introduction to IIC.

> 2. Subprocessors decode instructions and use them to run their
subsystems
> (i.e. error code display, motors, memory action log display, etc.)
> 3. (In most cases) Subprocs report back to main processor to confirm
that
> the task is done.
> The advantages of this system is that it is modular, expandable,
powerful,
> and very tight and tidy. I eventually plan to come up with a universal
> interface (PCI ports are a good example)

PCI is actually quite complicated.  Probably not the best choice.  This
sounds like a good fit for IIC as you suggested, especially since you have
one main controller that can be the master and all others can be slaves.

If you really want something a bit more robust and generic, the next
choice would be CAN.  Note that CAN is true peer to peer, not master
driven like IIC.  You can also get PICs with CAN built in.

> that will allow me to create new
> daughterboards and swap like mad, but this is not my focus right now.
> What PICs would you recommend for this? I'd like the main processor to
be
> quite powerful with plenty of spare I/O pins and as friendly to the
subprocs
> as possible.

Given that spec, the main processor should be a 18F452.  That's pretty
much the current top of the line.  Subprocessors that need less I/O could
be 18F252.  These are the 28 pin versions of the '452.  If you decide you
do want CAN (I still think IIC will do in this case), then use the 18F458
and 18F258.  They are mostly the same thing with CAN built in.

> So, as I said, point me to some resources, reccomendations,
distributors,
> etc. that will be useful when starting up a new PIC-based robotics
project.

Jameco is the best source for most general hobby electronics stuff.
Digikey has a much wider selection, but usually also higher prices and
higher quantities to get price breaks.  However, Jameco occasionally
prices some items high and their selection is surprisingly limited in some
areas.  PICs and crystals for PICs are two examples.


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