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Some rules on how to design a CAN network. Consider reading Problem Solving Questions.
The rules are general and valid for an CAN network including CANopen and Devicenet. Therefore look at Device Net Cable too.
- Always use twisted pairs for CAN_H and CAN_L
- Maximum cable length is between the two farthermost nodes on the CAN bus line. Remember, in the worst case a signal has to travel from the node at one end to the node on the other and of the line. It is a function of the bit rate as follows:
| bit rate | max cable length (in m) |
| 1Mbit/s | 25 |
| 800Kbit/s | 50 |
| 500Kbit/s | 100 |
| 250Kbit/s | 250 |
| 125Kbit/s | 500 |
| 50Kbit/s | 1000 |
(Table from CiA DS 301 4.02 page 20)
If you ask for a formula? There is one rule of thumb: cable length < 40000 Kbit/s * 1 m / BitRate in Kbit/s BitRate given in Kbit/s as well. Using this, results in < 40m for 1Mbit/s or < 320m for 125Kbit/s. In this formula a typical transceiver propagation of 25ns and a typical cable propagation of 5 ns/m is used for calculation.
CD-Systems provides a nice overview.
Cable types
All big vendors of specialized CAN cables
- Lapp UNITRONIC® BUS- CAN BUS CABLES, CAN BUS Cable, 120 Ohm BUS Cable for Static and Continuous Flex Applications
