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Communications Mechanism
Section 8-1
8-1
Communications Mechanism
8-1-1
Data Transmissions over the Network
In a Controller Link Network, token passing is used to control network access.
The right to send, called a “token,” circulates around the network. A node that
receives the token is allowed to send data. 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.
A token can be thought of as a circulating envelope. This envelope is circu-
lated through the network and the person who receives the envelope will put a
destination and a memo into the envelope to send his or her message to
somebody else. This method is called “token passing.” The Controller Link
Network is a bus network that uses token passing.
The overall network communications procedure is explained below.
1,2,3...
1.
The Unit at the node that manages the network, called the “polling node,”
transfers the token. The token is circulated through the network in ascend-
ing order of node addresses. One cycle in which the token is circulated
among all nodes on the network is called a “token circulation cycle.”
2.
After one token circulation cycle is complete, the polling node checks the
network connection status. One cycle in which the connection status of all
nodes on the network is checked is called a “polling cycle.”
3.
After one polling cycle is complete, the polling node transfers the token
again.
The procedure is then repeated. In a Controller Link Network, the total time
required for a token circulation cycle and a polling cycle is called the “commu-
nications cycle time.” Communications processing is executed by repeating
the communications cycle.
Controller Link
Token
(right to send)
Receive the token
When there is
data to send
Where there is
no data to send
Data
Attaches data to the token and send them together
Passes the token to the next node
Summary of Contents for C200HW-CLK21
Page 3: ...iv ...
Page 9: ...x ...
Page 12: ...xiii TABLE OF CONTENTS Index 367 Revision History 373 ...
Page 13: ...xiv ...
Page 19: ...xx ...
Page 57: ...32 Application Precautions Section 1 5 Example CX Programmer Response Timeout Setting ...
Page 69: ...44 Message Service Procedure Section 2 2 ...
Page 111: ...86 Constructing Networks with Repeater Units Section 3 4 ...
Page 154: ...129 Setting Data Links Section 5 2 Device Information Setting Data Link Tables ...
Page 261: ...236 Response Codes Section 6 7 ...
Page 297: ...272 Message Delay Times Section 8 4 ...
Page 353: ...328 Handling Precautions Section 9 6 ...
Page 364: ...339 Changing the Data Link Tables with Active Data Links Section 10 2 ...
Page 365: ...340 Changing the Data Link Tables with Active Data Links Section 10 2 ...
Page 369: ...344 Standard Models Appendix A ...
Page 391: ...366 Using the Relay Terminal Block Appendix C ...
Page 397: ...372 Index ...
Page 401: ...376 Revision History ...