solarwind wrote:
> Hey all! So far I am considering the RS485 bus for my inter-controller
> communication system.

If you're considerng RS-485 then you really should look at CAN.  It can work
on the same wires, but the low level protocol details are taken care of for
you in the silicon.  This includes collision detection and retry.  RS-485 is
a electrical spec only.  The protocol is totaly left as a exercise to the
implementer.  You have to think hard and write a bunch of code to deal with
multiple units possibly wanting to send at the same time, data integrity,
flow control, etc.

> That's because I understand how RS485 works.
> It's simple and very very flexible.

Just like CAN if you only look at the electrical signalling.

> Anyway, my question is: can ethernet be used as a BUS?

Yes, the original ethernet was a bus and the later "thin LAN" (10base-2 ?)
variant was also a bus.  However, ethernet is much faster and therefore
cable impedence is a important issue.  All ethernet bus implementations
require termination at each end of the bus, and all taps must be very short
and not mess up the bus impedence for signals going by.  While it is
possible to use ethernet this way if you can string one piece of 50ohm coax
past all locations, it's going to be a lot more trouble than you think.
Unless you really need the bandwidth (and apparantly not if you're
considering RS-485), then I wouldn't try ethernet for this app.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist