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3.6.1.2 NMT Node / Life guarding services
With the Node/Life guarding a NMT master can detect the failure of a NMT slave
and/or a NMT slave can detect the failure of a NMT master:
Node Guarding and Life Guarding:
With these services a NMT master monitors a NMT slave
At the
Node Guarding
the NMT master requests the state of a NMT slave in regular
intervals. The toggle bit 2
7
in the “Node Guarding Protocol” toggles after each request:
Example:
0x85, 0x05, 0x85 … --> no error
0x85, 0x05, 0x05 … --> error
Additionally if the
Life Guarding
is active, the NMT slave requests the state of a NMT
master in regular intervals, otherwise the slave changes into the PRE-OPERATIONAL
state.
The
NMT
services
for
Node/Live
guarding
use
the
function
code
1110 bin:
COB-ID 0x700+Node ID
.
Index
Description
0x100C
Guard Time [ms]
At termination of the time interval
Life Time = Guard Time x Life Time Factor [ms]
the NMT slave expects a state request by the master.
Guard Time = 0: No monitoring active
Life Time = 0: Life guarding disabled
0x100D
Life Time Factor
Table 5: Parameter for NMT services
3.7 PDO mapping
PDO mapping refers to the mapping of application objects (real-time data, e.g. object
6004h “Position value” from the object dictionary into Process Data Objects, e.g.
Object 1A00h (1
st
Transmit PDO).
The current mapping can be read via corresponding entries in the object dictionary,
the so-called mapping tables. The number of mapped objects that are listed
subsequently is found at the top of the mapping table (subindex 0). The tables are
located in the object dictionary at index 0x1600 ff. for the RxPDOs and 0x1A00ff for
the TxPDOs.
