CAN Bitrate Tolerance

[markus.ribler]

Hello everybody,

We use following PEAK products:
- PCAN-PCI Express FD (IPEH-004040)
- PCAN-USB FD (IPEH-004022)
- PCAN-USB (IPEH-002022)

We have 2 identical sensors connected to one port of the PCAN-PCI Express FD card. The sensors are configured to use different CAN IDs for sending values. As soon as the sensors are powered up they start sending messages (no startup messages have to be sent to the sensors). We use Bitrate 500k and the sensors send CAN 2.0A messages (11 bit IDs).

The messages from one sensor are received without errors. The messages from the second sensor are generating error-warn and bus-off signals.

We analyzed the messages with a LeCroix oscilloscope (with built-in CAN signal analyzer) and it confirmed that messages from 2nd sensor have errors in bit timing. It said also that bitrate from 1st sensor is 498k and 2nd is 497k.

We changed sample-points from small to large values, but still the same errors.

We also moved the sensors to different ports of the PCAN-PCI Express FD card and to a PCAN-USB FD dongle. No change, still the same errors.
But when using a PCAN-USB dongle (no FD) there are no errors anymore.

Questions:
- Are the CAN cores of PCAN-PCI Express FD card and PCAN-USB FD dongle the same? (Both have the same error)
- What is the tolerance of CAN bitrate? Is 497k still OK or should we tell the manufacturer of the sensors that the CAN bit rate is out of tolerance?

Thank you and best regards,
Markus Ribler

[M.Maidhof]

Hello Markus,

yes, all PCAN FD devices uses the same CAN-FD core. It looks like your are using a very intolerant bitrate settings with those FD cards, which will not accept the tolerance given by your sensor.

Please select a CAN-FD bitrate (and not a CAN2.0 bitrate) which uses the highest possible clock freqency of 80Mhz. Next, use a sample point of 75% and set Prescaler to 1 and the SJW to the highest possible value. Than you should be able to handle the bitrate tolerance of your sensors with the PCAN FD hardware modules.

Example for PCAN-View:

Bitrate.JPG (69.87 KiB) Viewed 11970 times

regards

Michael

[markus.ribler]

Hello Michael,
Thank you for the replay. I forget to mention that we use your products under Linux using SocketCAN interface. Here are the settings:

can-details.png (43.96 KiB) Viewed 11965 times

As I said we varied the sample-point value from 0.25, 0.5, 0.75 to 0.875. But the same errors occured.

I think there is already the 80Mhz clock in use. What else could we do?

Best regards,
Markus Ribler

[M.Maidhof]

Hi,

same here, please set the bitrate parameters in the SocketCAN driver with "ip link set" as they are displayed in my screnshot. At the moment you use sjw=1 which is bad when you have a big tolerance in the bitrate of your connected CAN nodes. And please note, that a samplepoint is only valid between 50% and 100%, so 25% is out of spec, 75% is the perfect set to have enough tolerance in both directions.

regards

Michael