Hi all. First off let me say I only tag along on this group as a second
source of info. I use PicBasic to program and cannot understand assembler at
all but still the engineering bits and pieces handy and informative. In no
way am I knocking assembler but am more knocking myself for not taking the
time to learn it.

Anyway the question.


I want to create a network of micro's. So far rs485 seems the go. What my
problem is how to get them all to talk and not have I suppose PACKET
colisions.

I have a PC that is connected to the world that I use as a Windows server
program. It is connected to the serial port and can send and recieve info
from that port.

I have several pics on the network.

I was going to make a hub or a main pic. One part of the hub connects to the
pc and another to the rs485.

What is a good way of getting these devices to communicate? I was going to
have each device listen for an incoming ID string but this meant (well in
pic basic anyway) that part of the time it was simply sitting there
waitning. If nothing came in it would go off and do the rest of the program
and then come back and listen again. How would the hub know it was sitting
there listening and simply the sending of the string and the waiting for the
incoming could be out of sequence thus missing each other.

I use a cat 5 cable for the network so I have 8 wires I can use.

Another idea was I use an additional wire other than what the data goes back
and foward on to send an id on. In picbasic you can use a command to send a
PULSE OUT of a certain length. I can then assign a ID to each unit and along
this cable send a lenght that matches the id. I have set up 2 pics and sent
a series of lengths to the second from 1000 to 5000 in steps of 20 and it
picks it up each time. So if we hang each device via a resistor and we have
the hub send a pulse out for say 500 millisecs and in each unit we have a
detection command in each cycle.

I think you get the idea. How do you guys do it? I am after a reliable way
to poll each unit. Additioanly if I could......be able to raise an alarm on
the hub if any of the units want to.

I have the software written to do the internet comms part and can get that
ifo from remote sites to the hub....

Ideas???????.......Suggestions???????........

Regards, Peter.

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