In a message dated 97-10-16 12:07:38 EDT, you write:

> Im working on a network using PICS.
>
>  All nodes on the network are identical, all joining onto a single bus -
>  ie each pic doesnt receive and the re-transmit the data.
>
>  (each pic is also programmed identicaly - including ID bits)
>
>  Can anyone think of a way to get each PIC to allocate itself a unique
>  number -  node ID. ... but if there are 50 PIC modules then I want the
>  numbers 1 to 50 or 0 to 49 for the numbers no more no less.

Several responses to this thread have mentioned use of random numbers with
repeated attempts whenever a collision occurs with a previously allocated ID.
This will cause very long delays for the last allocations. Unless I am
missing something in the specs, the introduction of random numbers seems to
be a needless complication. I make the assumption that the nodes are being
allocated and deallocated at random times instead of all turning on at once.
Is this assumption true?

If this assumption is true, each node can request ID allocation when it signs
on. Node 0 can assume the responsibility of sending the next available ID
number. If the request for an ID number times out, the node is the 1st one
and should be allocated as node 0.

The 7 byte bitmap suggested by Sean Breheny is a good way to keep track of
allocated IDs. If nodes can disconnect without notifying node 0 it may be
neccessary for node 0 to sequentially poll the nodes occasionally (one node
per second would verify the next every minute) to verify that each node is
still active.

Things could get complicated if node 0 disconnects without changing the ID of
the next node to 0 and passing on its responsibilities but this may be a rare
enough occurance to ignore.

>  I think I have a way of doing this but Im not saying anything right now.
>
>  Comms between modules are 1) TX/RX line 2) CLOCK 3) CTS
>
>  sort of a cut down serial com protocol
>

Is the TX/RX line one line that is shared for both sending and receiving or
are there separate lines?

>  Ideas anyone? ...
>
>  --
>  Jonathan Baker
>

Bob