Canbus Network design

Andrew Felsheim 3 months ago in IQANdesign updated by Gustav Widén (System support) 3 months ago 5

I have an existing design I have inherited which has 3 connected J1939 Canbus networks. Network 1 connects between an engine ECU and a MC2 Controller, Network 2 connects the MC2 and a MD4 Screen and Network 3 connects between the Controller, screen, and all our other CAN Devices; Radio, etc.

What is the point of Network 2, when they are already connected through Network 3? Is it because of it being a "Multi-Master" Device?

Thanks for the help!


Is network 2 the 'Diagnostic CAN' ? You can't send your own data over the diagnostic CAN so that might be why they are also part of network 3

It may be the diagnostic CAN, but I don't know how to confirm that. At the moment, I can only access this program via IQANRun5.


On my multi-master system I used two CANbus as well.

One for the IQAN Master bus, this does all the backend information and real-time stuff. The other I made J1939 and construct packets to efficiently transmit large quantities of data.

Maybe they did that.

Would you happen to know if a "Multi-Master" setup requires that IQAN Master bus?

Thanks for the help!


The Diagnostics bus is required in a multi-master system. 

If you for example connect to the PC on the MD4 to measure signals on the MC4, the data will be transferred over the diagnostics bus. The Diagnostics bus is also used for sending alarms from the MC4 that pop up on the MD4 and for showing signals from the MC4 on the MD4 display pages and in the MD4 menu system. When sending software updates, this is routed over the diagnostics bus. 

The amount of traffic on the diagnostics bus can vary quite a lot. For this reason, it is recommended to keep it as a separate bus. 

There is also a bus called Master bus, this optional and can be used for time critical real-time messages between master modules.