Seasons Greetings,

     I'm looking for a method to network several micros for real-time response
 in a robot.  One micro may be looking for obstacles in the robot's path, one
 may be counting pulses from the wheel encoders, one may be getting distances
 for wall-following, one may be working a manipulator, etc.  The point is that
 it is necessary for them to talk to one another, but not to all the others, and
 that some messages are more important than others (HEY - there's an immovable
 object dead ahead!).

1.  How are the micros hooked together, ie. what is the network topology?
    Use a common bus?  sequence through each?  Wire the micros that talk to each
 other together?

2.  How are messages assigned priorities?  Do/can they interrupt one another?
     Should a message priority be part of the message?  Is a Brook's style
 subsumption scheme plausible?

3.  How does a micro ready to send a message get the attention of the receiving
 micro?  Are interrupts necessary?  How is message contention resolved?
     Are interrupts a good idea, particularly when there's lots of messaging
 going on?

   I concerned about how many I/O lines are required for each micro-to-micro
 connection and the time it takes to pass a message around many micros, if that
 topology is used.  A message is a simple 24 bit serial transmission.

  Thanks and Merry Christmas,

John-