CAN Troubleshooting Guide
Manual • Doc.-No.: C.3032.21 / Rev. 1.1
CAN-CBX_Pt100
Page 40 of 120
7. CAN Troubleshooting Guide
The CAN Troubleshooting Guide is a guide to find and eliminate the most frequent hardware-error
causes in the wiring of CAN networks.
Figure. 18: Simplified diagram of a CAN network
7.1 Termination
The termination is used to match the impedance of a node to the impedance of the transmission line
being used. When impedance is mismatched, the transmitted signal is not completely absorbed by the
load and a portion is reflected back into the transmission line. If the source, transmission line and load
impedance are equal these reflections are avoided. This test measures the series resistance of the CAN
data pair conductors and the attached terminating resistors.
To test it, please
1.
Turn off all power supplies of the attached CAN nodes.
2.
Measure the DC resistance between CAN_H and CAN_L at one end of the network
(see figure above)
The measured value should be between 50
Ú
and 70
Ú
.
If the value is below 50
Ú
, please make sure that:
- there is no short circuit between CAN_H and CAN_L wiring
- there are not more than two terminating resistors connected
- the nodes do not have faulty transceivers.
If the value is higher than 70
Ú
, please make sure that:
- there are no open circuits in CAN_H or CAN_L wiring
- your bus system has two terminating resistors (one at each end) and that they are 120
Ú
each.