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connecting_can4vscp_devices_together

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Connecting can4vscp devices together

CAN4VSCP is a CAN based bus. This is the same communication system that is used in factories and in vehicles and it is very robust if installed correctly. The communication on a CAN network can use different bitrates from 10 Kbits/s to 1 Mbits/s. CAN4VSCP always use 125 Kbits/s.

Cable

CAT5e cable or better should be used. The most important thing with the selected cable is that CANH/CANL should be on a twisted pair.

Pinout RJ-XX

CAN4VSCP modules use a RJ-45 contact to connect to the communication bus. Normally you use a RJ-45 connector, but if you want you can use a RJ-11 or RJ-11 connector instead. Beware that you limit the power that can be transferred over the bus by selecting another contact then RJ-45.

CAN4VSCP modules use a RJ-45 contact to connect to the communication bus. Normally you use a RJ-45 connector, but if you want you can use a RJ-11 or RJ-11 connector instead. Beware that you limit the power that can be transferred over the bus by selecting another contact then RJ-45.

Pin Use Rj-11 RJ-12 RJ-45 Patch cable wire color
1 +9-28V DC RJ-45 Orange/White
2,1 +9-28V DC RJ-12 RJ-45 Orange
3,2,1 +9-28V DC RJ-11 RJ-12 RJ-45 Green/White
4,3,2 CANH RJ-11 RJ-12 RJ-45 Blue
5,4,3 CANL RJ-11 RJ-12 RJ-45 Blue/White
6,5,4 GND RJ-11 RJ_12 RJ-45 Green
7,6 GND RJ-12 RJ-45 Brown/White
8 GND RJ-45 Brown

Termination

The CAN4VSCP bus should be terminated with a 120 ohms resistor at both ends of the bus.

Terminators are needed to cancel signal echos in the cable. In short you get less noice in the cable if you use them. It is recommended to use them even if at 125 kbit it is possible that your bus will work anyway.

Cable length

CAN4VSCP always communicate with 125 Kbps. This means that if you use a good quality cable it can be up to a maximum of 500 meters using AWG24 or similar (CAT5) . Actual length depend on the environment and other parameters. Drops with a maximum length of 24 meters can be taken from this cable and the sum of all drops must not exceed a total of 120 meters.

Best practice

Even if it is possible to have cable lengths up to 500 meters it is better to stay at shorter distances to have some margins. Here are some guidelines for a reliable set up

  • Total cable length of 300m.
  • Stub cables count double their length in that total.
  • Nodes count as 6m in that total.
  • Never less than 30cm of cable between nodes, nor between a stub connection and a node.
  • No more than 50 nodes connected.

Following this best practice you will have a setup that will work reliable even in harsh environments.

A good paper is here and Steve Corrigan's classic paper is the final words on builing CAN bus systems.

Practical

A easiest and cheapest way to connect CAN4VSCP devices together is to use standard Ethernet cables and connectors. Use one T-connector at each node and use a short patch cable (must be >= 0.3m) to connect to the node. And then use standard Ethernet cables to connect T-connectors together. Each T-connector counts as a drop in your wiring budget.

You must remember to add a terminator at both ends (the last t-connectors on your bus).

This is how our ready made terminator looks like.

This is a setup for two devices.

Somewhere you have to supply power to the bus. This is easily solved with a RJ45 terminal block as of above which you just add to one T-connector block just as a node.

The components that is described here is available in all stores that sell network equipment and as a convenience to our customers we also carry them in the FrogShop.

A guide on troubleshooting CAN can be found here and here

connecting_can4vscp_devices_together.txt · Last modified: 2015/09/25 14:13 by akhe