Bus goes to "off" state

[JMEnhytec]

Hi all,

we are currently running a IPEH-003027 card and have the problem that the Bus sometimes goes into "off" state.
It used to happen every few days, now it happening more frequently, details as follows:


Bus is 250k
One device is connected to the bus that gets a request message and then returns 16 messages we receive. This is done in an endless loop at high rate (approx 40ms cycle time).
Both ends properly termined
Two different cables approx 3m were tested
It happens on both CAN Channels.
Mostly upon reading, rarely upon sending.
No Error frames are received prior to the problem (I hope I configured my bus correctly to receive those, but I am fairly certain)
The problem occurs between 10min and 3h
Voltage between pins 2/7 and pin 3 is 2V and 3V (a little out of spec?) when the cable is disconnected from the device and listening to an idle bus
Both the KDI LabView API and python-can can reproduce this problem

Is there anything else I can debug to dig into why this might occur?

Thank you for your help
Jakob

[M.Maidhof]

Hi,

a busoff means that the CAN-Controller detects a physical problem on the CAN during transmission. This can also happen when you send the same CAN ID from different nodes. Then the arbitration will not work and the frame data will cause a collision on the CAN. It could also be an EMC problem on your system, or the used bitrate settings doesn't fit exactly between the different CAN nodes (sample point, sjw, etc.).
After a busoff occur, you have to reset or reinit the hardware again, there are also automatic reset options on busoff available in our APIs. The API/driver sends a status message when a busoff occur.

regards

Michael

[JMEnhytec]

The flag for autorestart was already set in our setup, it did not manage to recover from this error.

We have now plugged the same cable into a USB-PCAN and the problem could not be reproduced for the past 20h.
It is possible our PCI Device is faulty or some of the other devices at the back panel of the PC caused interference.

[M.Maidhof]

Hi,

please check the transceiver voltages of the PCAN-PCI Express card as written in the following post: viewtopic.php?f=120&t=52

Please also check which bitrate settings are used in your software, please try to change the sample point and SJW of the used 250k bitrate.

regards

Michael

[JMEnhytec]

try to change the sample point and SJW of the used 250k bitrate.

does this apply to a non-FD CAN? We have fixed 250k

[PEAK-Support]

There is no "fixed" 250K - every CAN Setup have parameters like Sample Point, SJW etc.
The Arbitration Phase in FD is exact the same as in CAN2.0a/b (in FD called Nominal Bitrate)
If it works with a PCAN-USB, using a CAN 2.0a/b Device, please check the used Bitrate Timing of the 250K.
Use this Timing as Abitration (Nominall) Bitrate with your FD Device. As long as you do not use DLC>8 and do not use BRS, both are compatible.
Fore Calculation please check this page