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48 Fieldbus interface
3 Basics IL•1F CANopen DS301
0198441113586, V2.01, 11.2008
NMT message The NMT services for device control are transmitted as unconfirmed
messages with the COB ID = 0 . By default, they have the highest priority
on the CAN bus.
The data frame of the NMT device service consists of 2 bytes.
Figure 3.30 NMT message
The first byte, the "Command specifier", indicates the NMT service
used.
The second byte addresses the recipient of an NMT message with a
node address between 1 and 127 (7F
h
). A message with the node ad-
dress "0" is directed to all NMT slaves.
3.6.2 NMT services for connection monitoring
Connection monitoring monitors the communication status of network
devices, so a response to the failure of a device or an interruption in the
network is possible.
Three NMT services for connection monitoring are available:
• "Node guarding" for monitoring the connection of an NMT slave
• "Life guarding" for monitoring the connection of an NMT master
3.6.2.1 Node/Life guarding
COB ID Communication object NMT error control (700
h
+node-Id) is
used for connection monitoring. The COB ID for every NMT slave is de-
termined on the basis of the node address:
COB ID = function code NMTerror control (700
h
) + node-Id..
NMT-
Slave
NMT-
Slave
NMT-
Slave
NMT-
Master
0001
0
Command specifier
COB-ID
Node-ID
Byte 0 1
Command Specifier NMT service Transition
1 (01
h
) Start remote node A
2 (02
h
) Stop remote node B
128 (80
h
) Enter Pre-Operational C
129 (81
h
) Reset node D
130 (82
h
) Reset communication E