BECKHOFF FC5101 - Manual (Page 73)

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73
Trouble Shooting
Error Frames
One sign of errors in the CAN wiring, the address assignment or the setting of the baud rate is an increased
number of error frames: the diagnostic LEDs then show Warning Limit exceeded or Bus-off state entered.
Warning
Warning limit exceeded, passive error or bus-off state are indicated first of all at those nodes that
have detected the most errors. These nodes are not necessarily the cause for the occurrence of
error frames!
If, for instance, one node contributes unusually heavily to the bus traffic (perhaps because it is the
only one with analog inputs, the data for which triggers event-driven PDOs at a high rate), then
the probability of its telegrams being damaged increases. Its error counter will, correspondingly,
be the first to reach a critical level.
Node ID / Setting the Baud Rate
Care must be taken to ensure that node addresses are not assigned twice: there may only be one sender for
each CAN data telegram.
Test 1:
Check node addresses. If the CAN communication functions at least some of the time, and if all the devices
support the boot up message, then the address assignment can also be examined by recording the boot up
messages after the devices are switched on. This will not, however, recognise node addresses that have been
swapped.
Test 2:
Check that the same baud rate has been set everywhere. For special devices, if the bit timing parameters are
accessible, do they agree with the CANopen definitions (sampling time, SJW, oscillator).
Testing the CAN wiring
Do not carry out these tests when the network is active - communication should not take place during the tests.
The following tests should be carried out in the stated sequence, because some of the tests assume that the
previous test was successful. Not all the tests are generally necessary.
Network terminator and signal leads
The nodes should be switched off or the CAN cable unplugged for this test, because the results of the meas-
urements can otherwise be distorted by the active CAN transceiver.