Modbus TCP Server

[burscheservas]

Hi all,

I try to connect rapidscada directly to a PLC using Modbus TCP. The PLC has the libmodbus library implmented to establish the modbus connection.
The PLC can communicate with test software and also with the Modbus simulator (plcsimulator.org).

On the rapidscada side, I have been able to manage the connection from rapidscada to the Modbus Simulator as well. It works in principle.

If I add a new communication line with new object to the rapidscada configuration and set the communication to Modbus TCP Server (TcpPort = 502, behavior = slave, connmode = shared, devselmode = byipaddress) the connection can not be established.
I tried all possible combinations, but the tcpport 502 is not opening.
It seems that the TCP Server is not running correctly.

Do you have any idea/advice how to go forward to check the issue?

Thanks in advance.

Regards,
John

[Mikhail]

Hi,

Rapid SCADA works as TCP client, not TCP server. It connects to a PLC which is TCP server and PLC keeps port 502 open.

[burscheservas]

Hi Mikhail,

Thanks for the quick response!
This is unfortunately not good to hear for me.

Do you know maybe any stand alone Modbus TCP server software (open source / freeware) that can be used as software modbus TCP coupler?

Thanks

regards,
John

[Mikhail]

Hi John,

I researched for this, and I have’t found any free solution. We can develop such driver as a custom development by a contract.

[burscheservas]

Hi Mikhail,

Thanks for your reply and your offer.

Currently, I am investigating my options. Should I come to the requirement to use a customized solution I will come back to you.

Regards,
John

[Mikhail]

Hi John,

Sure. Any time. We provide high quality and competitive price 🙂

[Krzysztof]

Helo
I have a problem with communication with the slave simulator.
I can’t ask him for more than 127 registers. It does not appear to have such a limitation. Is there any restriction on Rapid Scada or modbus driver?

[manjey73]

Like this limitation of the Protocol on 256 bytes when using standard reading functions

[Mikhail]

Too big packets are not reliable. If you face limits in Modbus Template Editor, this is because of the Modbus standard.

[Krzysztof]

thx guys

[mauricio]

Hello, I have version 6.2.0.0 installed in Windows 10
I made a test project with modbus TCP
When starting the connection, it correctly makes the first 76 queries and then the communication fails.

++++++++  LINE LOG +++++++++++++++++++++++++

2024-03-06 15:02:26 Session with the device [1] Gen1
Request element group "FactEscG1"
Send (12): 00 49 00 00 00 06 01 03 C3 50 00 03
Receive (7/7): 00 49 00 00 00 09 01
Receive (8/8): 03 06 13 92 00 03 00 00
OK

2024-03-06 15:02:26 Session with the device [1] Gen1
Request element group "FactEscG1"
Send (12): 00 4A 00 00 00 06 01 03 C3 50 00 03
Receive (7/7): 00 4A 00 00 00 09 01
Receive (8/8): 03 06 13 92 00 03 00 00
OK

2024-03-06 15:02:26 Session with the device [1] Gen1
Request element group "FactEscG1"
Send (12): 00 4B 00 00 00 06 01 03 C3 50 00 03
Receive (7/7): 00 4B 00 00 00 09 01
Receive (8/8): 03 06 13 92 00 03 00 00
OK

2024-03-06 15:02:27 Session with the device [1] Gen1
Request element group "FactEscG1"
Send (12): 00 4C 00 00 00 06 01 03 C3 50 00 03
Receive (7/7): 00 4C 00 00 00 09 01
Receive (8/8): 03 06 13 92 00 03 00 00
OK

2024-03-06 15:02:27 Session with the device [1] Gen1
Request element group "FactEscG1"
Send (12): 00 4D 00 00 00 06 01 03 C3 50 00 03
Receive (0/7): 
Error: communication failed
Request element group "FactEscG1"
Send (12): 00 4E 00 00 00 06 01 03 C3 50 00 03
Receive (0/7): 
Error: communication failed</strong></blockquote>

++++++++ END  LINE LOG +++++++++++++++++++++++++

When applying restart line it again correctly does the first 76 queries and then communication fails.
The TCP server used works well with other scada software.
Please indicate steps to follow to solve the problem.

[Mikhail]

Hi,
In case of communication error, the driver should reconnect. What messages do you get after the error in the log?

Also consider increasing the timeout and delay parameters in the device properties in Communicator.

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