CTI 2572-A, Installation And Operation Manual

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CTI 2572-A Installation and Operation Guide
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Figure 2. PLC Server Function
illustrates the typical message dialog between the client, the 2572-A, and the PLC.
1) The client node sends a command message to the 2572-A via TCP/IP. For example, the
client may request that the 2572-A read and return 100 words of V memory.
2) Based on the contents of a command message, the 2572-A sends commands and data to the
PLC processor via the backplane. For example, the 2572-A would issue the applicable
command to the PLC to retrieve 100 words of V memory.
3) The PLC processor responds to the command via the backplane. In the example, the PLC
would return 100 V memory words.
4) After the PLC responds, the 2572-A builds the appropriate message and returns it to the client
node. In this example, the 2572-A would build a network message containing the 100 words
of data and send it to the client that requested it.
PLC Client Function
The 2572-A can also function as a PLC Client. As a PLC Client, the 2572-A acts as an agent for the
PLC, sending messages to other nodes and processing 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-A to send the message.
In the example above:
1) When the PLC detects a specified event, it sends a command to the local 2572-A module.
For example, the command could be to read 5 words from another node on the network.
2) Based on the command, the 2572-A 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-A processes the network message, and notifies the PLC that the operation is
complete. In the example, the 2572-A would write the words to the specified PLC memory
location and signal completion of the task.
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2) Command Message
Client PLC / 2572-A Server Node
1) 2572 Command
4) 2572 Response
3) Response Message
Figure 3. PLC Client Function