Download ModRSsim2 – Modbus RTU/ASCII Slave Simulator for Windows

ModRSsim2 is a free, open-source Modbus slave simulator for Windows that allows engineers and developers to simulate one or more Modbus RTU or ASCII slave devices on a PC. It is an essential tool for testing Modbus master applications, SCADA systems, and PLC communication routines without requiring physical hardware.

The simulator supports serial port (RS-232/RS-485) communication and can expose multiple slave device addresses simultaneously, each with configurable coil, discrete input, input register, and holding register data banks. Register values can be set manually or modified in real time while communication is active.

ModRSsim2 is widely used in industrial automation, building management systems (BMS), and energy monitoring projects where Modbus RTU is a common protocol. Its simple interface and zero-cost licensing make it a go-to simulator for automation engineers during development and commissioning.

Key Features

• Modbus RTU and ASCII support – Simulate slave devices using both RTU (binary) and ASCII transmission modes over serial ports.
• Multiple slave addresses – Configure and simulate multiple Modbus slave IDs on a single serial port simultaneously.
• All register types – Supports coils (0x), discrete inputs (1x), input registers (3x), and holding registers (4x).
• Real-time register editing – Modify register values on the fly while the simulator is actively responding to master requests.
• Serial port configuration – Configurable baud rate, data bits, stop bits, and parity to match your target hardware.
• Activity logging – Built-in communication log showing all received and transmitted Modbus frames for debugging.

How to Install

1. Download the ModRSsim2 package from the link below.
2. Extract the ZIP archive to any folder — no installation is required, it runs as a portable application.
3. Launch ModRSsim2.exe and select the serial port (COM port) to simulate on.
4. Configure the baud rate and serial parameters to match your Modbus master device.
5. Set the desired slave address(es) and configure register values, then click Start to begin responding to Modbus requests.