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CTI 2572 Installation and Operation Guide
6
PLC Client Function
The 2572 can also function as a PLC Client. As a PLC Client, the 2572 acts as an agent for the PLC;
it sends messages to other nodes and processes the responses under control of the PLC logic. Data in
the PLC program specifies the recipient and data contents of the message. PLC logic sets a “trigger”
bit to cause the 2572 to send the message.
In the example above:
1) When the PLC detects a specified event, it sends a command to the local 2572. For example,
the command could be to read 5 words from another node on the network.
2) Based on the command, the 2572 then sends the applicable command via TCP/IP to the
specified network (server) node.
3) The server node processes the command and returns a response via TCP/IP. In the example,
the server node would return a message containing the specified words.
4) The 2572 processes the network message and notifies the PLC that the operation is complete.
In the example, the 2572 would place the words in a specified PLC memory location and
signal completion of the task.
The 2572 can support multiple concurrent client sessions. The server node shown in the illustration
could be another 2572 or a computer programmed to process the commands and send the appropriate
responses. Information describing the PLC logic required for client operation can be found in
Chapter 3 of this manual.
The 2572 can support multiple server sessions and multiple client sessions concurrently. Therefore,
networked PLCs can use the facilities of the 2572 to participate in multi-session peer-to-peer
communications.
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5
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2) Command Message
Client PLC / 2572 Server Node
1) 2572 Command
4) 2572 Response
3) Response Message
Figure 6. PLC Client Function