Setting up Modbus RTU over TCP simulation

To debug software on a PLC, it was necessary to set up a simulation of a device that is polled via the Modbus RTU protocol. All the programs and actions listed below were performed in Windows OS.

For the simulation I used a combination of the following programs:

• Modbus Poll as a Modbus client

• ModRSsim2 for Modbus server simulation

• VESPE (Virtual Serial Ports Emulator (64 bit)),

I had some ancient version of VESPE – 1.0.5.443

The first thing you need to do is set up a virtual COM port. Launch VESPE and create a connector:

The PC where I installed the simulator already had some kind of COM port, so the example will be COM2:

After that, to connect to it via TCP, you need to create a TCP server that will open a port for communication over TCP:

We select the previously created COM port and assign the TCP port through which we will access the MOdbus client to read registers:

Next, we launch MODRSSIM (I installed it from the ModbusOPCServer demo trial package from MPSSoft (this is the one that MasterScada produces) and configure it to MOdbus RS-232, and also connect to COM2:

Let's fill in the holding registers:

Connect to ModbusPoll:

There is a connection, requests are coming, answers are coming:

I decided to write this article for myself as a cheat sheet. I believe that there are many such examples on the Internet. I would be grateful if you share your experience in simulating Modbus RTU, Modbus TCP devices based on Linux in the comments.