CANbus wiring schematic questions

[joseph]

Hi there,

I am looking for some guidance on physical wiring of a canbus for a race car.
The motec documents are a little unclear. I used M800 and PDM15 manuals to reference the CANBUS schematics

The physical nodes are C125, PDM15, Motec UTC adaptor (#61059), Vipec ECU
The Vipec ECU has a internal terminating resistor between can-hi and can-lo and the vipec manual says it must be a terminal node on the CANbus.

A few questions:

1. Both PDM15 and Motec M800 schematics show terminating 100 ohm resistors on both ends of canbus along with a UTC connector as a node. However the manuals also mention that the motec UTC adaptor 61059 has an internal terminating resistor (measured by me as 100 Ohms between can-hi and can-lo). If I wired as per the schematics this would mean there are THREE resistors (two at each end of the bus and one internally at the UTC adaptor). Would this be correct?

2. Does the UTC connector need a terminal node on the canbus or can I have an anywhere along the bus as long as it is within 500 mm of the end?

3. Both PDM15 and Motec M800 schematics show UTC connector wired to CAN-HI and CAN-LO and 0V. However only the M800 schematic shows UTC connector wired to 8V. Does the UTC connector/adaptor require 8V to function? If so, I do not have a Motec ECU - can I wire this to the Vipec 8V out?

Thanks for your time

[PQatPIT]

1. Yes, correct.

2. UTC seems to be happy wherever it is wired to.

3. No need for 0V nor +8Vdc supply. UTC doesn't need these. I have never wired these and all systems have worked properly.

[joseph]

Thank you!

[greenamex2]

Also thanks..was going to ask that myself!

[adrian]

PQatPIT is correct, I though I would add a bit more information for reference.

You basically want to wire a CAN bus as a long trunk with branches that come off it. The two terminating resistors are then placed at either end of the trunk, which is usually the longest distance between any two CAN devices on the bus. If the Vipec ECU has an inbuilt resistor then ideally it needs to be at one end.

You can put the UTC anywhere you like (between the two end nodes), just think of it as any other CAN device. It is fine to have the additional resistor when the UTC is connected, it is more important to have two resistors when the UTC is not connected (ie when the vehicle is actually running) than having too many when you connect to the ECU/PDM etc.

The 8V and 0V are only needed if you are using a old style parallel port CAN cable that was originally used when the M800 first came out. The UTC only requires CANHi/Lo as it is powered via the USB port on your laptop.

Adrian