BUDE_Manual-CANopen_EN.doc
17/55
Baumer Hübner GmbH
23.10.2012/bja
Berlin, Germany
Node and Life Guarding
The
CAN in Automation
association CiA
recommend to use the new heartbeat protocol
(see next chapter). To use the node guarding
instead of heartbeat protocol bit 5 of object
2110h has to be set.
To detect absent devices (e.g. because of bus-
off) that do not transmit PDOs regularly, the
NMT Master can manage a database, where
besides other information the expected states
of all connected devices are recorded, which is
known as Node Guarding.
With cyclic node guarding the NMT master
regularly polls its NMT slaves. To detect the
absence of the NMT master, the slaves test
internally, whether the Node Guarding is taking
place in the defined time interval (Life
Guarding).
The Node Guarding is initiated by the NMT
Master in Pre-Operational state of the slave by
transmitting a Remote Frame.
The NMT Master regularly retrieves the actual
states of all devices on the network by a
Remote Frame and compares them to the
states recorded in the network database.
Mismatches are indicated first locally on the NMT Master through the Network Event Service. Consequently
the application must take appropriate actions to ensure that all devices on the bus will got to a save state
"Communication error Object 1029h-1h".
Example for a nodeguarding protocol:
COB-ID
Data/Remote
Byte 0
701h
r
00h (0d)
701h
d
FFh (255d)
701h
r
00h (0d)
701h
d
7Fh (127d)
Possible NMT node states:
0:
BootUp-Event
4:
Stopped
5:
Operational
127:
Pre-operational
In other words, the encoder is in the pre-operational mode (7Fh = 127).
