68300

Hello all,
 
I am using a CAN bus (now at 500 kHz and about 35 meters length) with 36
identical nodes using the 68376.  My loading on the bus is probably about
8%.  And for the most part according to the error flags and counters within
the TouCAN module, there seems to be very few errors on the bus.  If I
connect a PC (with an aftermarket CAN bus card) to the network, my bus
loading may go up about 15%.  However, at that same time on the
oscilloscope, I begin to see a rhythmic bundle of CAN messages passing
through the screen trace, and I see that the bit stuffing errors begin to
increase noticeably from the 68376.  If I speed up the machine that all of
this is operating, I will also begin to see format errors and others error
counters increase as well, even to the point of going from the "error
active" to the "error passive" state.
 
Has anyone seen this before?  I am not sure if we have a slight speed
mismatch in the CAN bus speed settings between the PC and my 68376 nodes, or
too much capacitance from the cable and interconnecting plugs between the
nodes, or if there is something else going on.  Unless things get really
bad, the machine seems to work fine, but I do not know how many CAN bus
errors (or types of errors) should be considered normal.
 
Any comments or suggestions would be greatly appreciated.
 
Thanks to all,
Jim
 


[Non-text portions of this message have been removed]

Jim,

Is your PC on one end of the 35 meters?  If so, you have a length issue.
Otherwise I would suspect bit-timing settings on the PC CAN card.

At spec length (30 meters for 500 kHz), you should expect to see *no*
errors on the CAN bus.  One error once in a while is probably no big deal
and could be considered normal.





"Godiska, Jim" <jgodiska@...> on 08/30/2002 06:30:02 PM

Please respond to 68300@yahoogroups.com

To:    68300@yahoogroups.com
cc:

Subject:    [68300] CAN bus errors


Hello all,

I am using a CAN bus (now at 500 kHz and about 35 meters length) with 36
identical nodes using the 68376.  My loading on the bus is probably about
8%.  And for the most part according to the error flags and counters within
the TouCAN module, there seems to be very few errors on the bus.  If I
connect a PC (with an aftermarket CAN bus card) to the network, my bus
loading may go up about 15%.  However, at that same time on the
oscilloscope, I begin to see a rhythmic bundle of CAN messages passing
through the screen trace, and I see that the bit stuffing errors begin to
increase noticeably from the 68376.  If I speed up the machine that all of
this is operating, I will also begin to see format errors and others error
counters increase as well, even to the point of going from the "error
active" to the "error passive" state.

Has anyone seen this before?  I am not sure if we have a slight speed
mismatch in the CAN bus speed settings between the PC and my 68376 nodes,
or
too much capacitance from the cable and interconnecting plugs between the
nodes, or if there is something else going on.  Unless things get really
bad, the machine seems to work fine, but I do not know how many CAN bus
errors (or types of errors) should be considered normal.

Any comments or suggestions would be greatly appreciated.

Thanks to all,
Jim



[Non-text portions of this message have been removed]



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