Wiring Notes
CAN-CBX-AI420
Manual • Doc.-No.: C.3030.21 / Rev. 1.4
Page 35 of 103
5.3 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 in the net!
*
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
5.4 Bus Length
*
Optical couplers are delaying the CAN signals. By using fast digital isolators and testing each board
at 1 Mbit/s, esd modules typically reach a wire length of 37 m at 1 Mbit/s within a closed net
without impedance disturbances like e.g. longer stub.
Bit-
Rate
[kBit/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
37
25
800
59
50
666 6
.
80
-
500
130
100
333 3
.
180
-
250
270
250
166
420
-
125
570
500
100
710
650
83 3
.
850
-
66 6
.
1000
-
50
1400
1000
33 3
.
2000
-
20
3600
2500
12.5
5400
-
10
7300
5000
Table 12: Reachable wire lengths depending on the bit rate when using 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.
