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Manual_CANopen_StrainLink_EN_V3_05.doc
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10 9
8
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4
3
2
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0
Node 1
Node 2
Node 3
DATA
Node 3
Bus
S
O
F
Identifier
R
T
R
I
D
E
DLC
Node 3
DATA
Node 3
r
0
DLC
DLC
Node 3
DATA
1
2
3
4
Arbitration
Fig. 1 Principle of bitwise bus arbitration -- Nodes 1, 2 and 3 simultaneously start an arbitration process. At
Time 2, Node 2 determines that the bus does not have the recessive level it sent and terminates its
arbitration process. At Time 3, Node 1 gives up. At Time 4 (end of the arbitration process), Node 3 transmits
its data.
4.2.5
Priority-oriented message transmission
The arbitration process described above guarantees at any time that the message with the highest priority is
sent in each case as soon as the bus is free. The priority of the message is specified using the value in the
Message identifier. The smaller this value, the higher the message priority. The principle of priority-oriented
messages allows a very efficient utilization of the bandwidth available for data transmission. In this way, it is
possible to fill the bus 100% with low-priority messages without noticeably delaying the transmission of
messages having higher priority. A maximum latency of about 130 µs results for the message having the
highest priority at a transmission rate of 1 Mbit/s.
4.2.6
Identifier distribution
As standard, Message identifiers of 11 bits in length are used in communications via CANopen. Thus, the
range of 0 to 7FF
H
is available.
The identifier distribution is designed so that, in one CANopen network, a maximum of 128 devices are
present: one NMT master and up to 127 NMT slaves.