Hi,
as I am facing some major issues with my CAN bus in the field which I am trying to identify with the PCAN-MiniDiag FD I would like to get detailed information about CAN Min/Max.
It says (compared to CAN Voltages):
CAN Min/Max: Measurement of minimum and maximum voltage values for CAN-High and CAN-Low in the range from -5 to +8 V
CAN Voltages: Measurement of dominant and recessive levels for CAN-High and CAN-Low in the range from -5 to +8 V
So do I get voltages (even spikes) on CAN Min/Max screen and actually interpretated signal levels on CAN-Voltages screen?
As I have quite big spikes in my signal edges and the problem of occasional unknown high levels at end of frame (see attached picture) it would be very helpful to know if I see the high spikes end of frame on CAN Min/Max or only those that are long enough to be intepretated as dominant level.
Thanks in advance,
Christoph
Interpretation of CAN Min/Max
Interpretation of CAN Min/Max
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Re: Interpretation of CAN Min/Max
Hello,
the two screens "CAN Min/Max" and "CAN Voltages" use the same raw data, it is only a different way the data are presented.
If GND of all devices is the same:
A recessive CAN-level is ~ 2.5V for both CAN-H and CAN-L.
A dominant CAN-level is ~ 3.5V for CAN-H and ~ 1.5V for CAN-L.
The analog samples are taken close to the configured sample point, which is derived from the bit rate definition.
If the spike is short enough (e.g. only the first 30% of a bit) this voltage value will not be measured. Measurement of the analog value of the bus voltage start at 50% of a bit time, sample point for a bit is typically between 70..95% of a bit.
On your scope-screen there is a higher amplitude bit at the end of a CAN-frame (trigger point). This is the "ACK" bit, all devices on the network send this bit to acknowledge the correct reception of a CAN-frame. A higher amplitude of this bit is normal.
Do you see in the "Statiscics" screen an ErrorCnt that is rising? This would be an indication of CAN Errors on the CAN-Bus. Maybe the error counter is rising in a cyclic way? Maybe you can remove single CAN-devices from the bus and see if the errors disapper.
Check that the same CAN-Identifier is not transmitted from several nodes. If this CAN-Frames collide it will most likely create a CAN-Error.
Check the CAN termination. Ideal value would be 60 Ohm, 55..65 Ohm are OK.
You can scan the bit rate several times. You should always get the same result. If one node has a slightly different bitrate (e.g. 505kbit/s instead of 500kbit/s), this could be a reason for sporadic CAN-Errors.
Regards,
Gunnar Bohlen
the two screens "CAN Min/Max" and "CAN Voltages" use the same raw data, it is only a different way the data are presented.
If GND of all devices is the same:
A recessive CAN-level is ~ 2.5V for both CAN-H and CAN-L.
A dominant CAN-level is ~ 3.5V for CAN-H and ~ 1.5V for CAN-L.
The analog samples are taken close to the configured sample point, which is derived from the bit rate definition.
If the spike is short enough (e.g. only the first 30% of a bit) this voltage value will not be measured. Measurement of the analog value of the bus voltage start at 50% of a bit time, sample point for a bit is typically between 70..95% of a bit.
On your scope-screen there is a higher amplitude bit at the end of a CAN-frame (trigger point). This is the "ACK" bit, all devices on the network send this bit to acknowledge the correct reception of a CAN-frame. A higher amplitude of this bit is normal.
Do you see in the "Statiscics" screen an ErrorCnt that is rising? This would be an indication of CAN Errors on the CAN-Bus. Maybe the error counter is rising in a cyclic way? Maybe you can remove single CAN-devices from the bus and see if the errors disapper.
Check that the same CAN-Identifier is not transmitted from several nodes. If this CAN-Frames collide it will most likely create a CAN-Error.
Check the CAN termination. Ideal value would be 60 Ohm, 55..65 Ohm are OK.
You can scan the bit rate several times. You should always get the same result. If one node has a slightly different bitrate (e.g. 505kbit/s instead of 500kbit/s), this could be a reason for sporadic CAN-Errors.
Regards,
Gunnar Bohlen