Hi Nelson

Go with CAN. It takes some study to get it up and running because the
controller is pretty advanced but once it's on air, it won't come off. We
have a test setup running in the office (DeviceNet) and it only stops when
you take of both terminators or only leave one node on the bus. We're
develloping the units while they are on the bus, and it doesn't give a
hitch.

The biggest advantage of the CAN network as I see it now is the easy of
actually doing the communication. You just have to write a few registers and
the rest is done by the controller. The only thing you need is a line
driver, but I thing you need that as well for the 485 option on these
network sizes. The length of the network can be handled at lower speeds, but
you have a very low bus usage, so that won't be a problem. One thing to keep
in mind is the number of network nodes. The MCP2510 can handle 127 nodes (if
I'm well informed), so it's possible you need a repeater somewhere on the
net, however, those can come off the shelf.

Regards,

Claudio

-----Oorspronkelijk bericht-----
Van: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]Namens Nelson Hochberg
Verzonden: vrijdag 16 augustus 2002 21:57
Aan: PICLIST@MITVMA.MIT.EDU
Onderwerp: [PIC]: CAN or RS-485 ?


I am planning a system with a network of PICs.  The PICs will be daisy
chained together (power and communications) in a standard office environment
(fluorescent lights, networked PCs, telephones, HVAC, etc.)  The PICs will
need to communicate about two bytes (status change of nine LEDs and which
PIC sent the event) every 5-10 minutes.  Two of the events are pretty
important and would need to be acknowledged by the other PICs.  Initially,
the network will be 300' end to end with 18 PICs.  The network could expand
to 2000' end to end and about 100-200 PICs.

I've got it whittled down to either a CAN or RS-485 (unless someone can
convince me another protocol would be better.)  Which one do you think is
better and why.

If I use 18F248/448 do I need to use a transceiver interface such as
PCA82C250 or can the PICs connect to the wires directly?  Any
recommendations for an interface?

I was thinking of using the MAXX485 if I went with RS-485.  Any other
suggestions?

TIA

Nelson
nelson@nosuffering.com
www.nosuffering.com

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