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ModRSsim2 Modbus Slave/Server RTU/TCP and DF1 Simulator
If you are looking for a Modbus RTU/TCP Slave/Server simulator software under Windows, have a look at
- FREE software
- Simulate up to 255 Modbus slaves
- Open source
- Supports ALL Modbus data types
- Diagnostic view that shows you the traffic
- Supports scripting for simulation
If any .dll files are missing when launching ModRSsim2, please install Visual Studio 2010
You will find many links on the Internet concerning this software, but some of them are old or are paid versions!

For a Modbus RTU/TCP Master, take a look at the ModbusDoctor – a great Modbus Master Windows Software (Use the keyboard 1 or 0 for change Bit values)