View source for Modbus TCP

==Introduction==
Modbus TCP is a Modbus variant used for communications over TCP/IP networks, connecting over port 502. It does not require a checksum calculation as lower layers already provide checksum protection.
Note that this is not the same as as Modbus over TCP/IP.
For background information on Modbus and its different variants please see the [http://en.wikipedia.org/wiki/Modbus Modbus article in Wikipedia].
Modbus is often used by PLC's.

==AlphaCom and the Modbus TCP protocol==
AlphaCom can send out status information in the Modbus TCP protocol via an EDO-port.
* Select an available EDIO port, for instance EDIO 1
* TCP/IP client
* Enter the IP address of the PLC to connect to
* Enter the Port nr. which is used by the Modbus TCP protocol, by default 502

==Modbus TCP protocol - AlphaPro programming==
The exact meaning of databytes will depend on the specific installation and PLC used. This article gives an example of an implementation for a real installation. Please modify as appropriate for the actual requirement.
In this example the AlphaCom sends status information about each intercom station to a PLC, which uses this information for visualisation. The status is coded in a single byte, where each bit has a specific meaning.
* Bit #0: Intercom station is OK and ready for use
* Bit #1: Faulty line or faulty station
* Bit #2: Intercom station in conversation
In this example the information is written to specific registers in the PLC, 1 register for each intercom station. The PLC registers to use are from 50001 and up, the intercom stations have directory number 101 and up.
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Example: Station line error
Progam an event:
* Owner Type: Station with UDP 8
* Event Type: 13 - Faulty station line
* When Change To: ON
* Action string: EDO 1 "\0\x01\0\0\0\x06\x02\x06%dfmt(%op(%1.dir,+,49900),X,4)\0\x02"
In this specific case the meaning of the bytes is:
* \0\x01 - Transaction Identifier; 2 bytes
* \0\0 - Protocol Identifier; 2 bytes; always '0' for Modbus TCP
* \0\x06 - Length Field; 2 bytes; Number of remaining bytes in this frame 
* \x02 - Unit Identifier; 1 byte; Slave Address (255 if not used) 
* \x06 - Function code; 1 byte; Function codes as in other variants 
* %dfmt(%op(%1.dir,+,49900),X,4)\0\x02 - Data bytes; n bytes; Data as response or commands 


[[Category:3rd party integration]]