Modbus Simulator Guide

About

The Modbus Simulator is a Modbus Server that can be used as an endpoint for testing communication with the Modbus Device Service Component.

Running

Environment Variables

As the simulator can run in either TCP or RTU modes, an environment variable, RUN_MODE must be set to specify which mode to run in.

Option	Expected Values	Description
RUN_MODE	TCP / RTU	Controls whether the simulator will run as a TCP or RTU device

Note

If this is not set, the device will default to TCP

Downloading the Simulator

docker pull iotechsys/modbus-sim:1.0

Running the simulator

To run the TCP simulator:

docker run --rm --name modbus-sim iotechsys/modbus-sim:1.0

Alternatively, if you want to run the RTU variant in a dockerized format, use the following command instead:

docker run --rm --name modbus-sim -e RUN_MODE=RTU iotechsys/modbus-sim:1.0

Stopping the simulator

docker stop modbus-sim

Networking Configuration

TCP

If the TCP version of the simulator is being run on a separate host from the Modbus device service, the following flag must be included in the docker run command:

--network=host

If the TCP version simulator is running on the same host as the Modbus device service, run the simulator as instructed. Once running find the IP of the docker container with the following command:

docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' modbus-sim

Using this IP, set the device address in the relevant device file.

RTU

To connect to the RTU version of the simulator on the same host as the Modbus device service, run the simulator as instructed. Once running find the IP of the docker container with the following command:

MODBUS_SIM_ADDRESS=$(docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' modbus-sim)

With socat, create a serial connection to the container using its IP and set the port to /tmp/virtualport

(socat pty,link=/tmp/virtualport,raw,echo=0 tcp:${MODBUS_SIM_ADDRESS}:50103) &

In the device file, set the address of the device to /tmp/virtualport to make it reachable in conjunction with the above socat command.