Node Guarding - Mitsubishi Electric MELSEC iQ-R Series User Manual

1.8

Node Guarding

The NMT master uses the node guarding function to monitor NMT slaves to detect errors in them.
Function details
The NMT master (1) polls each NMT slave (2) periodically for monitoring. And, each NMT slave monitors polling from the
NMT master.
(1)
: Polling
: Response
• Node guarding produces a heavy load on the bus, so it is recommended to use heartbeat instead.
• When the NMT master is enabled, if node guarding and heartbeat consumer are set to the same node ID,
the node guarding setting for that node ID is disabled because a conflict occurs between heartbeat and
node guarding.
• When the NMT slave is enabled, if node guarding and heartbeat producer are set, the node guarding setting
is disabled because a conflict occurs between heartbeat and node guarding.
■Error detection by the NMT master
The NMT master (1) monitors polling responses from each NMT slave (2) to detect the NMT state and errors of the NMT
slave. If the NMT slave does not send a valid response within the node life time, the NMT master determines that an error has
occurred in the NMT slave. Also, if the NMT state of the NMT slave is different from the latest NMT state instructed from the
NMT master to the NMT slave through node control, the NMT master determines that an error has occurred in the NMT slave.
In this case, the CAN ERR LED of the NMT master turns on or flashes.
(1)
(2)
: Polling
: Response
NMT slave information detected by the NMT master is reflected in the following buffer memory areas.
Buffer area name
NMT error control status
1 FUNCTIONS
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1.8 Node Guarding
(2)
(2)
Node lifetime
GuardTime GuardTime
Details reflected
For node guarding for each NMT slave, the following statuses are stored.
• Node guarding is enabled/disabled (running/stopped).
• There is no response from an NMT slave within the guard time. Or, an invalid response is received.
• There was no response from an NMT slave within the node life time.
• The NMT state of an NMT slave is different from the expected state.
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