Modbus RTU over TCP: question

General Discussion
1

Hello All:
Ignition provides two Modbus drivers: Modbus TCP and Modbus RTU over TCP. I’m familiar with Modbus RTU and Modbus TCP. What is Modbus RTU over TCP? How can we connect to RTU devices using this driver? Could any one give some ideas please?

Thanks,
Shwetha.

2

This is only useful when you have a dumb TCP-to-Serial device in front of a Modbus RTU device.

This protocol is worst case scenario because you are now on TCP but there’s no header or sequence numbers to match up requests/responses, and if your converter device allows multiple connections you can end up with multiple masters writing to the same serial line out of turn…

If you have an older Modbus RTU device it’s ALWAYS preferable to put a dedicated Modbus TCP gateway in front of it instead.

2 Likes
3


How to connect a serial Modbus-RTU to Modbus-TCP (Query/Response) using Anybus Communicator.

4

I am attempting to do something similar. Can you recommend a good Modbus TCP Gateway. I’m just concerned about compatibility.

Thanks

5

Moxa MGate gateways have been a popular and reliable choice.

6

Good Afternoon Kevin,

Do you know of anyone that has used the Moxa Mgate? I have a MB3180 but havent been able to get a Modbus RTU connection. It is trying but just goes from connecting to disconnected. I have tried with a direct connection and a switch(moxa switch as well). I can connect using the moxa Mgate Manager and i can ping the device.

Any Ideas?

Eric

7

Many people use the MGate.

You should be making a Modbus TCP connection to it, not RTU or RTU over TCP.

1 Like
8

Thanks Kevin,

I got it working. For some reason in the manager software it wasn’t switching to slave mode. It connects now after going into the Mgate webserver and making the changes there.