Network Parameters - Omron SYSMAC 3G8F5-CLK11-E Operation Manual

Communications Cycle Time
9-1

Network Parameters

9-1-1 Controller Link Communications
Polling Node
9-1-2 Communications Cycle
Token Cycle
Polling Cycle
Refresh Cycle Time
158
This section explains how to use Controller Link Network communications and
how to adjust the network parameters to match the system.
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 sent between the vari-
ous 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
together. If the node has no data to send, it will pass the token to the next 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 net-
work from shutting down.
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.
Communications cycle
Token cycle Polling 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.
The refresh cycle time will vary depending on factors such as the communica-
tions cycle time, the number of data link words, and so on.
The refresh cycle time value can be displayed by the Controller Link Support
Software's data link status monitoring function. There is no refresh cycle time for
the Support Board, because the data link areas are constantly refreshed by the
data link data that is received. When the refresh cycle time for the Support Board
is read by the Controller Link Support Software, therefore, the value will always
be 0.
Communications cycle
Token cycle Polling cycle
Section 9-1