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A customer already wired an installation like it's shown in the diagram. The
communications are made using CAN at 250 kb/s.

I would like that someone guides me on how to connect the nodes so I can
have a reliable network.

The CAN standard specifies a max length of 250m for 250kb/s, and a max stub
length of 10m.

First of all, I do not understand what it is exactly Tpropseg, used on the
calculation of the line lengths.

Now, all the cables are CAT5 wires, the same used con Ethernet networks. One
solution was to simulate a line going back and forth using different pairs,
like Dwayne suggested, but the bus length will be around 700m, which is a
lot more that 250m :)

I first thought of using a hub, but now I saw on the standard that the like
can be evenly balanced, in my case it will have termination resistors on
every node that will be of 390 ohm. That will give me the ~60 ohm impedance
I need...

Is that correct? Does someone has any other suggestion?

Mauricio Jancic
Janso Desarrollos
Microchip Consultant Program Member
info@janso.com.ar
www.janso.com.ar
+54 11 4542 3519
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of Vitaliy
> Sent: Wednesday, February 22, 2006 11:23 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE]CAN Protocol wiring
> 
> "Mauricio Jancic" wrote:
> >            I have an already installed wiring in a factory with CAT 5
> UTP
> > cable. The wire is not used at the moment and its installed in a star
> > topology. At the center of the wiring I would like to put a CAN device
> and
> > there would be another can device on each end of the cables.
> >
> >            I understand that this will not work for CAN since it would
> > need
> > a BUS with the shortest possible stubs.
> 
> I don't see why not. What's the data rate, and how long is each segment?
> 
> > Now, how can I make (or where can I
> > buy) a hub for this type of connection? Anyone sell it? Oh, I'm using
> > micrchip's MCP2551 as the physical interface.
> 
> I don't understand exactly what the problem is, and why you want to use a
> hub to solve it.
> 
> Best regards,
> 
> Vitaliy
> 
> --
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