Correct Wiring of Electrically Isolated CAN Networks
5. Correct Wiring of Electrically Isolated CAN Networks
For the CAN wiring all applicable rules and regulations (EC, DIN), e.g. regarding electromagnetic
compatibility, security distances, cable cross-section or material, have to be met.
5.1 Heavy Industrial Environment (
Double
Twisted Pair Cable)
5.1.1 General Rules
Note:
esd only grants the compliance with directive 2004/108/EC, if the CAN wiring is carried
out with single shielded double twisted pair cables that match the requirements of ISO
118982-2 (table 9).
The following
general rules
for the CAN wiring with single shielded
double
twisted pair cable must
be followed:
1
A cable type with a wave impedance of about 120 Ω ±10% with an adequate wire cross-section
(0.22 mm²) has to be used. The voltage drop over the wire has to be considered!
2
For heavy industrial environment use a four-wire CAN cable. Connect
•
•
•
two twisted wires to the data signals (CAN_H, CAN_L) and
the other two twisted wires to the reference potential (CAN_GND) and
the cable shield to functional earth (FE) at least at one point!
3
The reference potential CAN_GND has to be connected to the functional earth (FE) at exactly
one
point.
4
A CAN bus line must not branch (exception: short cable stubs) and has to be terminated with the
characteristic impedance of the line (generally 120 Ω ±10%) at both ends (between the signals
CAN_L and CAN_H and
not
at GND)!
5
Keep cable stubs as short as possible (l < 0.3 m)!
6
Select a working combination of bit rate and cable length.
7
Keep away CAN cables from disturbing sources. If this can not be avoided, double shielded cables
are recommended.
Figure. 3:
CAN wiring for heavy industrial environment
Page 12 of 23
Hardware Manual • Doc. No.: C.2021.21 / Rev. 1.1
CAN-PCI/200
CAN GND
CAN_L
CAN_H
CAN_GND
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
n.c.
CAN_L
CAN_H
CAN_GND
Shield
CAN_GND
twisted
twisted
5
6
7
9
8
1
4
3
2
9
1
4
5
6
7
3
8
2
Single shielded
double twisted pair cable
(four-wire cable,
2x 2x 0.22mm²)
wire shield
earth (FE)
Wire Layout
(Example)
Signal assignment of single shielded double twisted pair cable
with earth and termination
n.c. = not connected
DSUB9 connector
(female or male)
pin designation
connector case
DSUB9 connector
(female or male)
pin designation
CAN cable with connectors
connector case
