ModRSsim2 hasn't been updated in years and struggles on modern Windows systems. ModbusSimulator is the modern replacement — actively maintained, native Windows 10/11 support, TCP + RTU + ASCII, Master and Slave modes.
No credit card · No registration · Windows 10/11 (64-bit)
ModRSsim2 was built for Windows XP-era DPI (96 DPI). On modern high-DPI monitors, the interface appears blurry or elements are misaligned. ModbusSimulator is built for Windows 10/11 with proper DPI awareness.
ModRSsim2's last meaningful update was years ago. Bug reports go unfixed. Compatibility issues with newer USB-to-serial adapters (FTDI, CH340, CP2102) are common. ModbusSimulator was last updated April 2026.
ModRSsim2 primarily supports Modbus RTU. Its TCP support is basic and often problematic with modern network configurations. ModbusSimulator has full Modbus TCP, RTU, ASCII, and UDP support.
ModRSsim2 only simulates a Modbus slave. If you need to also run as a Modbus master to poll real or simulated devices, you need a separate tool. ModbusSimulator includes both Master and Slave modes.
ModRSsim2 cannot simulate Modbus exception responses. You can't test how your master handles errors. ModbusSimulator supports configurable exception injection (01–11).
ModRSsim2 always responds immediately. Real-world devices have response latency. ModbusSimulator lets you configure response delays in milliseconds to test timeout and retry handling.
| Feature | ModRSsim2 | ModbusSimulator |
|---|---|---|
| Windows 10/11 native support | DPI scaling issues | ✓ Full support |
| Last updated | ~2015 (no active maintenance) | April 2026 |
| Modbus RTU (serial) | ✓ | ✓ |
| Modbus TCP | Limited/buggy | ✓ Full support |
| Modbus ASCII | ✗ | ✓ |
| Modbus UDP | ✗ | ✓ |
| Slave (server) simulation | ✓ | ✓ |
| Master (client) mode | ✗ | ✓ |
| Exception response injection | ✗ | ✓ |
| Response delay simulation | ✗ | ✓ |
| Live request log | Basic | ✓ Full with timestamps |
| CSV register import/export | ✗ | ✓ |
| Multiple slave instances | Single | ✓ Up to 8 simultaneously |
| USB-to-serial (FTDI, CH340) | Driver issues | ✓ Compatible |
| Price | Free (open source) | Free 30-day trial / $59 one-time |
Built natively for modern Windows with proper DPI scaling. Works on 4K monitors, laptops, and Surface tablets without blurry text or misaligned controls.
No more needing two applications. Run as a Modbus slave to accept master connections, or as a master to poll real and simulated devices — simultaneously.
All four Modbus protocol variants in one license. Switch between them without reinstalling or changing your test setup configuration.
Configure the slave to return exception responses (01–11) for specific register ranges. Test how your master handles errors — something ModRSsim2 can't do.
Add configurable delays (1ms to 30,000ms) to simulate real-world device latency. Verify your master's timeout and retry logic under realistic conditions.
Import register maps from CSV files to quickly load a full device register configuration. Export current values for documentation or team sharing.
ModRSsim2 is a free Modbus slave simulator popular in the mid-2000s. Engineers are moving away from it because it hasn't been maintained in many years, has DPI scaling issues on Windows 10/11, lacks proper Modbus TCP support, has no Master mode, and cannot simulate exception responses or response delays.
Yes — ModbusSimulator is built and tested for Windows 10 and Windows 11, including 64-bit environments, high-DPI displays, and modern USB-to-serial adapters (FTDI FT232, CH340, CP2102). ModRSsim2 often has compatibility problems on these modern systems.
ModbusSimulator costs $59 as a one-time license. However, it includes a full-featured 30-day free trial with no credit card and no feature restrictions. Try it completely free before buying. ModRSsim2 is open-source and free but comes with the maintenance and compatibility tradeoffs described above.
Yes, and more. Both can simulate Modbus slave devices with configurable Coils, Discrete Inputs, Holding Registers, and Input Registers. ModbusSimulator additionally supports exception injection, response delays, multiple simultaneous slave instances (up to 8), auto-updating register values, and CSV register import.
Download ModbusSimulator — the modern, actively maintained Modbus simulator that works on Windows 10/11 with full TCP, RTU, ASCII, and UDP support.