CANopen allows 127 devices (the bus master and 126 remote slaves). Transmission speed depends strictly on the type of used cable.
In the CAN protocol frame priority is managed by collision between dominant and recessive levels of the line. This collision must be resolved during transmission of a bit, which limits the signal propagation delay between 2 nodes.
The following tables specify the maximum trunk cable length based on the CANopen cable provided by Schneider Electric (TSXCANCA•••, TSXCANCB••• and TSXCANCD•••).
Consequently, the maximum distance between the 2 most distant nodes of a CAN bus depends on the speed and is provided in the following table:
|
Speed in bit/s
|
Maximum Cable Length
|
|
1 Mbit/s
|
20 m (65 ft)
|
|
800 kbit/s
|
40 m (131 ft)
|
|
500 kbit/s
|
100 m (328 ft)
|
|
250 kbit/s
|
250 m (820 ft)
|
|
125 kbit/s
|
500 m (1640 ft)
|
|
50 kbit/s
|
1000 m (3280 ft)
|
|
20 kbit/s
|
2500 m (8202 ft)
|
|
10 kbit/s
|
5000 m (16404 ft)
|
According to the Schneider Electric network strategy, the speeds 1 Mbit/s, 800 kbit/s, 500 kbit/s, 250 kbit/s and 125 kbit/s are recommended for automation solutions at machine and installation level.
NOTE: The maximum length assumes a reasonable device internal propagation delay and bit sampling point. Devices that present long internal propagation delays will effectively reduce the maximum cable length that could otherwise be realized.
The cable lengths of the above table may include a drop cable if it is at the physical end of the trunk cable.
Repeaters Reducing Cable Length
The above values specify the maximum cable length without any repeater. As repeaters add a propagation delay in the bus, this delay reduces the maximum length of the bus. A propagation delay of 5 ns leads to a length reduction of 1 m (3 ft).
Example. A repeater with a propagation delay of 150 ns reduces the maximum cable length by 30 m (98 ft).
Maximum Cable Length vs. Number of Nodes
In addition to the length limitations based on the transmission speed, the maximum cable length is also influenced by the load resistance.
In any case, the maximum number of nodes that may be connected on the same segment is restricted to 64. To connect more nodes to 1 segment, use a repeater.
The table below shows the influence by the number of nodes on the cable length:
|
Number of Nodes
|
Maximum Cable Length
|
|
2
|
229 m (751.31 ft)
|
|
16
|
210 m (688.97 ft)
|
|
32
|
195 m (639.76 ft)
|
|
64
|
170 m (557.74 ft)
|
Electrical Isolation of CANopen Devices
In documents about CANopen you will often find the value of 40 m (131 ft) maximum value at a transmission speed of 1 Mbit/s. This length is calculated without electrical isolation as used in the Schneider Electric CANopen devices.
With such electrical isolation the minimum network length calculated is 4 m (13 ft) at a transmission speed of 1 Mbit/s. However, the experience shows that 20 m (65 ft) are the practical length that could be shortened by drops or other influences.
