Omron CVM1-CLK21, Operation Manual

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194
Communications Mechanism Section 8-1
If the node is always to be connected as a polled node when the power is
turned on, set it as a polled node. If the node can become a polling node
when the power is turned on, set it as a polling node. One of the nodes set as
a polling node will serve as the actual polling node. Except for maintenance
after Unit replacement (see 9-5 Handling Precautions), set the Units all nodes
as polling nodes (set the polling node/polled node bit to
“
0
”
).
8-1-3 Network Parameters
Network parameters are also used to control network operations. Network
parameters are read from the polling node and distributed to all other nodes
when the Controller Link Network is started. In this way, all nodes on the net-
work always have the same network parameter settings. If nodes are con-
nected to the network halfway during network operation, the network
parameter settings will also be distributed to these nodes when they are con-
nected. The following three network parameters can be specified.
Maximum Node Address This parameter specifies the maximum node address of nodes to be checked
by the polling node. The default is 32. Reducing the setting of this parameter
reduces the number of nodes checked by the polling node and can thus
avoids unnecessary check operations. However, if the network contains
nodes with node addresses greater than the setting of the parameter, these
nodes will not be connected to the network.
No. of Polled Nodes per
Communications Cycle This parameter specifies the number of nodes to be checked (polled) by the
polling node during each polling cycle. The default is 4. Setting this parameter
to a high value increases the communications cycle time, but reduces the time
required to recognize that nodes have been removed from or added to the
network. Reducing the setting of this parameter shortens the communications
cycle time but delays a network response when a node is disconnected from
or connected to the network.
No. of Event-frames per
Communications Cycle This parameter specifies the maximum number of event frames (communica-
tions other than data links, such as message service transmissions) that can
be transferred during a communications cycle. Specify a value in units of 128
bytes. The default is 35 (128
×
35 = 4,480 bytes).
Increasing the setting of this parameter increases the communications cycle
time but allows for more event communications such as the message service.
Too small a parameter value restricts event communications, resulting in an
error. See 8-2 Communications Cycle Time (on page 195) for the effects of
network parameters on communication cycle times.
8-1-4 Specifying Network Parameters
The network parameters can be specified from the Controller Link Support
Software. This section describes only the allowable setting range for each net-
work parameter. Refer to the Controller Link Support Software Operation
Manual (W308) for setting procedures.
The following table shows the setting range and default for network parame-
ters.
Network parameter Setting
range
Default
value
Maximum node address 2 to 32 32
Number of polled nodes per communications cycle 1 to 31 4
Maximum no. of event-frames per communications
cycle 6 to 238 35