termination

[jgkempen]

I need help checking the wiring and termination on my system.  An EE grad student at my school had set up the system last year and being an ME undegrad I was just hoping it would be right.

The device I am working with has five terminals- one for batt, one for ground, one for can -, one for can +, and one for ignition.  Right now I have supplied power to my device through the batt and ground terminals, and plugged can - into pin 2 and can + into pin 7 of the cable from my can card.  I have tried communicating with the device but all I ever get is this error:

"Error 0xbff6206b (CanErrCommNoAck); CAN bus problems (no ack) caused all communications to stop.  This error corresponds to CAN Bus Off state.  Solutions: Verify that cabling is correct, devices are connected and operational, and proper bus power is applied."

Of course this has naturally led me to believe something is wrong with the wiring.  Could improper termination cause this error?  Right now there is not a 120 ohm resistor across the can +/- terminals.  Should I place a resistor across those terminals?  If this error is not a termination problem is there any other common problems i should check?

[jgkempen]

I just checked and I believe the device I am connecting is internally terminated since the resistance I measured between can h and can l terminals on the device is approx 120 ohms.  So if termination is the problem the only place i could see is on the other end at the can card in the computer.  The EE working on the project last year said he was under the impression that the pc adapter was internally terminated as well.  Is the end where the 9 pin cable plugs into the computer already correctly terminated or do i need to use a 120 ohm resistor there?  I tried to measure the resistance between can l/h terminals at the computer but I never really got a good measurement.

If termination is not the problem anyelse  have any other ideas because I am running out.

[DirkW]

Hi JGKempen,

What kind of CAN device are you using? Is it a low speed device, which is terminated on the board or is it a high speed device, which is not terminated internaly?

perhaps the student has addad the termination inside the connector for the CAN device?

To your device: perhaps you have to power the ignition pin too to get the device running?

A second thing you should check is whether or not your CAN device is internaly powered or externaly powered. Check the blue jumper on the board. If it is externaly powered, connect battery and ground to the Cable as well. (Pin 9 and Pin 3)

DirkW

[jgkempen]

The device I am using is a high speed can device.  It is a radar from an active cruise control system.
The card I am using is a PCI-CAN/XS.

As far as needing to power the ignition, I have tried and not had any success.  It caused  voltage to fluctuate alot and nothing else noticeable.

As far as I know my device is externally powered- I have been hooking up power terminals to a power supply and its supposed to work in the 9-14v range.  Since it is externally powered you say I need to also supply the power and ground to  (Pin 9 and Pin 3) to get it to work? I kinda wondered about this, I Will try to see it that fixes it.

Thanks

[JB]

Of course this has naturally led me to believe something is wrong with the wiring.  Could improper termination cause this error?  Right now there is not a 120 ohm resistor across the can +/- terminals.  Should I place a resistor across those terminals?  If this error is not a termination problem is there any other common problems i should check?

The lack of termination resistors and/or an inadequate cable may in fact cause this error. Please see pages 4-4 and following of the NI-CAN Hardware and Software Manual.