8-1
Section
Network Parameters
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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 interferences 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 connected. If
the node has data to send, it will attach the data to the token and send them to-
gether. 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.
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 ad-
dress 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, set-
tings, 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 “com-
munications cycle time,” and each communications cycle is divided into a “token
cycle” and a “polling cycle” as shown in the following diagram.
Token cycle
Polling cycle
Communications cycle
Token cycle
Polling cycle
Communications 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.
The polling cycle is the period during which the polling node checks the status of
the nodes in the network. The polling node checks whether each node is actually
participating in the network, whether there are any new nodes participating, and
so on, and notifies all the nodes of the results of the check.
The refresh cycle time is the time, during data link operation, from when the con-
tents of the data link areas are refreshed until the next time they are refreshed.
Polling Node
Token Cycle
Polling Cycle
Refresh Cycle Time
