• Influx Technology

CAN-Bus Troubleshooting Guide

Introduction

CANBUS is a high-speed network which requires high quality wiring in order to operate properly. As such, it is sensitive to improper wiring. The majority of CANBUS communication problems are caused by poor wiring, incorrect termination, or the use of multiple frequencies on the same bus.


The Controller Area Network (CAN) is a bus structure originally designed for automotive

applications, but it has also found its way into other areas. The CAN bus is a balanced (differential) 2-wire interface running through a shielded twisted pair (STP). Several different data rates are defined by the standard, with 1 Mb/s being the fastest & 125Kb/s the slowest for CAN. Issue in the physical layer of CAN network can lead to failure of nodes or corruption of messages transmitted in the bus. Most of the problems discussed in the article can introduce intermittent error frames, it can even lead to failure of the BUS. We often get away with these issues at low baud rates. Errors tend to start becoming particularly noticeable around 250kbps.


Most common CAN Bus physical layer problems are.

  • Improper CAN Termination.

  • Improper CAN Voltage levels.

  • Improper grounding.

In this article we will discuss on how to identify and resolve these issues.


CAN Bus Termination

The termination is used to match impedance of a node to the impedance of the transmission line being used. This is required to avoid reflections that are caused by digital data communications. The resistors act as an “electrical shock absorber” and if they are not fitted correctly, the digital signals will “bounce” off the end of the data Bus, causing noisy reflections. This will have a significant effect on the performance of the CAN Bus. If the source, transmission line and load impedance are equal these reflections are eliminated.

This test measures the series resistance of the CAN data pair conductors and the attached terminating resistors.

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