Peter May wrote:
> <snip>

Have you thought about using CAN? I'm working on a similar project
(network of pic's) that I was going to use 485 for. CAN handles all of
the collision and retransmit in hardware, which is nice. The down side
is that the CAN protocol doesn't assign an address to each node, instead
it uses message types. It does however allow a node to request a
particular type of message from other nodes, which would handle your
polling requirement. Microchip has a few appnotes that explain it in
better detail.

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