WAGO I/O System 750 Series Manual page 71

CAN_High and CAN_Low are two physically different bus levels.
The cable screen is connected to the drain connection.
This is terminated with a 1 MΩ resistor to the DIN rail via the clip on the bot-
tom of the Coupler/Controller. The DIN rail must then be directly connected
to the Grounding Stud that must be connected to Earth Ground. We strongly
recommend a central Earth Ground for the entire DeviceNet Bus conductor
screening. A low Ohm connection of the screening on PE terminal can only be
made externally.
Note
WAGO offers the screen connection system (series 790) for an optimum con-
nection between fieldbus cable screening and functional earth.
Each DeviceNet node forms the differential voltage U
U
CAN_High
Differential signal transmission offers the advantage of an insensitivity com-
pared to common mode malfunctions and ground offset between the nodes.
Note
At its conductor ends, the bus cable must always be connected with a match-
ing resistor of 120 Ohm to avoid reflections and, as a result, transmission
problems.
This is also required for very short conductor lengths.
The CAN bus is a 2-wire bus and bus error management can detect a cable
break or a short-circuit by the asymmetric operation.
Further information
The CiA provides documents regarding specifications, especially cable specifi-
cations on the Internet under:
http://www.can-cia.de
WAGO-I/O-SYSTEM 750
DeviceNet
- U . using the bus levels CAN_High and CAN_Low.
CAN_Low
DeviceNet
Network Architecture
with: U =
Diff Diff
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