Help with basic Can network

Hi Guys,

Sorry if these seem like simple questions but I am new to this and can't seem to find answers to some of the more basic questions that apply to my build

I am in the process of completely wiring a simple car and I want to take advantage of CAN as much as possible.

I have the below components that I want to communicate through CAN

ECU master Black

ECU master PMU 16

ECU master ADU 5 dash

ECU master GPS module

ECU master Canbus Keypad

ECU master USB to CAN module

My questions are about layout and wiring.

My first question is, CAN1 or CAN2? - The Dash and PMU have 2 CAN outputs and can communicate by either CAN 1 or CAN 2, my understanding from reading the manuals is that I should use CAN1 for the CAN to USB module to allow communication between the PC and dash or PMU. The EMU Black has only 1 CAN output

Do I connect all of the individual components onto CAN1 and ignore CAN2? is there a reason why I should split them and if I do, can they still communicate with each other?

My simplistic idea was that I should create a CAN loop for CAN 1 with a 120-ohm resistor at each end and then link into this loop with every component. I have attached a basic picture (CAN network) of what I was thinking for a layout (I know the CAN network wires will need to be twisted, I just used straight lines for simplicity)

For some context and what I am trying to achieve, I am using the PMU to power the fuel pump and cooling fan so I would like to use the ECU to trigger these components over CAN, for example, when the engine ECU sees a temperature I determine, the ECU will instruct the PMU to turn the fan on.

Equally, I would like to display coolant temperature, RPM, oil pressure, fuel pressure, etc from the ECU sensors on the dash, again sent over the CAN network. will the layout I have suggested enable this?

Another question, I am using a premade ECU master loom for the ADU dash, this loom has a comms port to directly connect to the ECU master USB to CAN device to the CAN network on the Dash, if this is all connected to CAN1, will I be able to use this to communicate with the the other devices on the CAN network or will I need to have additional points added to communicate with each device?

The Black ECU has a micro USB port on it, so I presume this will be used for mapping?

One last question regarding the locations of the 120-ohm resistors, I have seen some people connect the resistor directly to the plug of the device at the end of the CAN network, see the other picture I added, (CAN network 2)

When looking at the manuals they never show this but it does seem to make things slightly easier, is this appropriate, bad practice, unreliable or is it completely normal and acceptable practice?

As ever thanks in advance and sorry for the silly questions

Your first task is to determine what the required (or allowed) bus speed is for each CAN device. You can only put devices operating at the same bus speed on the same bus. From memory, I think the ECU Master Keypad had a requirement for a specific bus speed and specific bus on the PMU. Get that sorted first, plus any additional requirements.

Once you know what devices are going onto what bus, you decide how to create a chain that connects all the devices on the same bus. Each device many have only a single CAN bus, or more than one (so CAN1 / CAN2). So for example the PMU might communicate (at 1Mbit/s) with the ECU and Dash on it's CAN1, but the ECU might be connected to it's CAN2. The PMU's CAN 2 might be used for the keypad (again, check the ECUMaster docs -- it was clear what was required).

Good luck. This is not a trivial project even though you say it's a "simple car".

Thanks David,

I have been reading through all the ECU master documentation and all of the components I am using communicate as standard at 1Mbps, CAN 1 is fixed at 1Mbps and CAN2 has configurable speed, so this would be used if I had a different dahs that needed 500Kbps for example.

I also found a sample layout of a CAN network in the ECU master documentation that is pretty much what I have, see attached picture.

So, I guess that resolves most of my questions, I just need some advice on how best and where to install the resistors on the network.

Kind Regards

Ricky

I would install them just like the drawing, either at the connector to the last device on the chain, or if the device has switchable CAN resistor then turn it on in the device.

Ricky,

Yes all devices you mentioned can run at 1Mb. You could stick everything on one bus as long as you won't be overloading it. That would leave a second bus free in case you want to add a device later which can't operate at 1Mb.

What's shown in the PNG file would also work.

Terminating resistors can be placed in the connector for a device at end of line, but I prefer doing it externally with a unit that can be unplugged for diagnostics, or to more easily add a device later. As much as we try to plan harnesses out and build them so nothing will ever have to change, sometimes we need to make changes or additions later.

You calibrate the PMU by connecting your laptop to the CAN USB adapter, and the ECU does use a USB connection.