For bus line outside and inside of control cabinet:
- Modbus-cable (shielded twisted pair, wave-impedance 150Ω).
- Exception for short bus lines (up to 100m):
some non standard Modbus-cable as shielded twisted pair with wave
impedance 120Ω (see CAN-cable) is allowed to use.
For derivation-cable between node and bus line (up to 20m):
- shielded twisted pair
1. Organisation of electrical bus line:
The CAN-H, CAN-L and shield (CAN-GND) must be looped through
from node to node.
CAN bus line must be organised according to line-structure
(node-1, node-2 … node-N).(see picture).
2. Termination of twisted pair in bus line:
connect between CAN-H and CAN-L one resistor 120 Ω on the begin of bus line
and one resistor 120 Ω on the end of bus line.
3. Conditions by each node (CAN-Port by ECU) on the bus line:
- shield must be connected to terminal “CAN-GND”, signal lines CAN-H and
CAN-L to signal terminals (idenical designation).
- By removing of one node-device the CAN-communication between other
nodes
must work without interrupt (requirements acc. ISO 11898-2:2003).
- DC-decoupling between CAN-port (CAN-GND, -H, -L) and PE (frame)
is required.
4. Type of bus line isolation and the application fields:
In general there are two different types of bus lines.
Isolated and non isolated.
If one or more nodes on the line don’t have galvanic isolation – this bus is called
non isolated.
In general:
- use isolated bus line for communication with external customer modules.
- for communication, localised internally in one control cabinet only, it is al-
lowed to use a non isolated bus line.
5. Connection to PE by isolated bus line (see point-4):
the shield of can-bus must be connected to PE (mounting plate)
in one point only.
6. If required, use a CAN-repeater for isolation.
Consider time delay for signal conversion by CAN-repeaters and limit the cable
length or reduce the data transmission baud rate
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