Omron CS1W-RPT01, CVM1-CLK21 Communications Mechanism, Data Transmissions over the Network

Communications Mechanism Section 8-1

8-1 Communications Mechanism

8-1-1 Data Transmissions over the Network

Controller Link

Token

(right to send)

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.

Receive the token

Data

When there is data to send

Attaches data to the token and send them together

Where there is no data to send

Passes 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.

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