Bus length
The maximum length of a CAN bus is primarily limited by the signal propagation delay. The multi-master bus access procedure (arbitration) requires signals to reach all the nodes at effectively the same time (before the sampling within a bit period). Since the signal propagation delays in the CAN connecting equipment (transceivers, opto-couplers, CAN controllers) are almost constant, the line length must be chosen in accordance with the baud rate:
|
Baud rate |
Bus length |
|---|---|
|
1 Mbit/s |
< 20 m* |
|
500 kbit/s |
< 100 m |
|
250 kbit/s |
< 250 m |
|
125 kbit/s |
< 500 m |
|
50 kbit/s |
< 1000 m |
|
20 kbit/s |
< 2500 m |
|
10 kbit/s |
< 5000 m |
*) A figure of 40 m at 1 Mbit/s is often found in the CAN literature. This does not, however, apply to networks with optically isolated CAN controllers. The worst case calculation for opto-couplers yields a figure 5 m at 1 Mbit/s - in practice, however, 20 m can be reached without difficulty.
It may be necessary to use repeaters for bus lengths greater than 1000 m.