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Network Parameters
Section 8-1
8-1
Network Parameters
This section explains how to use Controller Link Network communications
and how to adjust the network parameters to match the system.
8-1-1
Controller Link Communications
The token bus method is used for communications in the Controller Link Net-
work. With this method, a piece of data called a “token” is passed between the
various nodes in the network. The only node that can transmit data at any
given time is the one that currently holds the token, thereby preventing inter-
ferences to data transmission within the network.
The token travels from smaller node addresses to larger, and then back to the
beginning again, without regard to the order in which the nodes are con-
nected. If the node has data to send, it will attach the data to the token and
send them together. If the node has no data to send, it will pass the token to
the next node.
For Wired or Optical Networks, or Optical Ring Networks in Token Bus Mode,
a token is passed between nodes connected in a daisy-chain bus called a
token bus. With an Optical Ring Network in Token Bus Mode, this is called a
token ring because the bus is connected in a ring. With a token ring, two
transmission paths can be used (transmission path duplication) to create a
more robust system.
Polling Node
Each Controller Link Network always has a Unit that controls communications
within the network. This Unit is called the
“
polling node.
”
Normally, the node
that has the smallest node address in the network is the polling node. All Units
at nodes other than the polling node are called
“
polled nodes.” The polling
node controls the token, checks the network, and performs other relevant
tasks. Should the polling node break down, the node with the next smallest
node address is automatically selected as the polling node to prevent the
entire network from shutting down.
Note
There are times when the node with the smallest node address will not be the
polling node depending on the order in which the nodes are started, models,
settings, and node status.
8-1-2
Communications Cycle
The “communications cycle” is the cycle for repeating Controller Link Network
processing. The time required for one communications cycle is called the
“communications cycle time,” and each communications cycle is divided into
a “token cycle” and a “polling cycle” as shown in the following diagram.
Token Cycle
The token cycle is the period during which the token is sent from the polling
node to the nodes in order and returned to the polling node. During this cycle,
any nodes with data to send will send that data. Data link data will also be
sent during this cycle.
Token cycle
Polling cycle
Communications cycle
Token cycle
Polling cycle
Communications cycle
Summary of Contents for SYSMAC 3G8F7-CLK12-EV1
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Page 4: ...iv ...
Page 20: ...xx Conformance to EC Directives 6 ...
Page 48: ...28 Applications Precautions Section 1 4 Example CX Programmer Response Timeout Setting ...
Page 68: ...48 Backup Power Supply Wiring Optical Ring Systems Only Section 2 4 ...
Page 74: ...54 Using the C Library Section 3 2 ...
Page 110: ...90 Changing the Data Link Tables with Active Data Links Section 5 5 ...
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