Correctly Wiring Electrically Isolated CAN Networks
6.3 Electrical Grounding
●
For CAN devices with electrical isolation the CAN_GND must be connected between the
CAN devices!
●
CAN_GND has to be connected to the earth potential (FE) at
exactly one
point of the
network!
●
Each
CAN interface with electrical connection to earth potential
acts as an earthing point.
For this reason do not connect more than one
CAN device with electrical connection to
earth potential
!
●
Earthing can e.g. be made at a connector/T-connector.
6.4 Bus Length
●
Optical couplers are delaying the CAN signals. esd modules typically reach a wire length of
37 m at 1 Mbit/s within a closed net without impedance disturbances like e.g. cable stubs
>> 0.3 m.
Bit rate
[Kbits/s]
Typical values of reachable
wire length
with esd
interface
l
max
[m]
CiA recommendations
(07/95) for reachable wire
lengths l
min
[m]
1000
800
666.6
500
333.3
250
166
125
100
83,3
66.6
50
33.3
20
12.5
10
37
59
80
130
180
270
420
570
710
850
1000
1400
2000
3600
5400
7300
25
50
-
100
-
250
-
500
650
-
-
1000
-
2500
-
5000
Table 7:
Recommended cable lengths at typical bit rates (with esd-CAN interfaces)
Note:
Please note the recommendations according to ISO 11898 for the selection of the cross
section of the wire depending of the wire length.
Page 22 of 29
Hardware Manual • Doc. No.: C.2041.21 / Rev. 1.2
CAN-PCI/405-B4