Data exchanges take place in one of two modes:
NOTE: The maximum Ethernet frame size depends on the type of transaction. The maximum frame size is 256 bytes for messaging.
The RTU module is used to manage these TCP connections using messaging:
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servers (32 connections)
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clients (16 connections)
TCP/IP reserves specific server ports for specific applications through IANA (Internet Assigned Numbers Authority). Modbus requests are sent to registered software port 502.
Port 502 messaging paths:
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server path:
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Port 502 messaging can process up to 8 incoming requests from the network. Requests are received during the previous scan and sent to the Modbus server in the IN section.
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Port 502 messaging can process up to 8 responses from the Modbus server in the IN section (including writing the data into the socket).
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client path:
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Port 502 messaging can process up to 16 outgoing requests from the application in the OUT section (including writing the data into the socket).
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Port 502 messaging can process up to 16 incoming responses from the network in the IN section. Responses are sent to the application.
