On 2/23/06, Mauricio Jancic <info@janso.com.ar> wrote:
>
> 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



Hi Mauricio,

I don't know how cost sensitive your application is but can't you just use
five adapters like the CANUSB (http://www.canusb.com/) or similar (CAN232
http://www.can232.com/ if you don't have an USB capable host). Use 120 ohm
terminations on each segment.  On the host use a daemon app that handle the
interfaces. If you have a host that  lives on WIN32 or UNIX my canald daemon
(http://www.vacp.org) will do this out of the box for you.

Another solution is to build a board with multiple MCP2515 which would be
fairly easy to do. I have one such board in progress and it will be
available this spring on the VSCP site.

You can of course also lower speed and daisy chain the nodes. If you want a
bullet proof solution I recommend the first approach.

Regards
/Ake

>
>
>
>
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