How to Determine What is on the CAN Data Bus

During the development cycle of a project you may be working on setting up your CAN bus devices from data sheets or you may not have any data sheets to reference. It is extremely helpful to know exactly what is on the data bus and how each device is sending their data and what source addresses they are using.

For example a CAN device may say they are using only the first two data bytes of a message but they send a packet of 8 data bytes with the unused data bytes stuffed with 0xFF. If you set your FreeForm message in Powervision up with a byte length of 2 bytes the message will not be received.

To capture this information you need a CAN data logger or CAN Analysis tools. CANCapture is the tool we primarily use however if you do not have this resource available PowerVision Configuration Studio offers a CAN data logging feature that allows you to capture CAN bus activity and export it to a .csv file. Click on the following links to learn more about each of these options.

Two Ways to View CAN Data on the Bus

1. Use CANCapture with an ECom Cable to view live CAN data and Save Data Logs
   • Article: Using CANCapture Tools
2. Use a Display running our CAN Datalogger configuration, then analyze the .csv output file
   • Download: CAN Data Logger Configuration

What to Look for on the CAN BUS

Source Address - Find the source address of each device broadcasting on the data bus and identify what the devices are. Unplug each device one at a time to verify its address.

Parameters - Look for the parameter of interest to see which device is sending it. Look for duplicate parameters coming from multiple devices for conflict.

Protocol - Are the messages CANopen with 11 bit message ID or J1939 with 29 bit message ID.

Data Length - Maximum data length is 8 bytes however it may be less. Make sure this is accounted for.

Rate - How often is the message being transmitted.

DM1 Fault Messages - Fault code will point to a problem that needs to be corrected.  Verify they are displayed correctly. Are the fault messages getting sent as a single message or in a Multipack (special protocol to handle more than 8 bytes of data). What are the lamp codes.

Abnormal Events - Use graphing to capture the state of various parameters when a abnormal event occurs.

Data Log Playback - playback a data log to recreate an issue.