Open ModSim is a free implimentation of modbus slave (server) utility for modbus-tcp and modbus-rtu protocols.
The following Modbus functions are available:
- Discrete Coils/Flags
0x01 - Read Coils
0x02 - Read Discrete Inputs
0x05 - Write Single Coil
0x0F - Write Multiple Coils
- Registers
0x03 - Read Holding Registers
0x04 - Read Input Registers
0x06 - Write Single Register
0x10 - Write Multiple Registers
0x16 - Mask Write Register
The following simulations are available:
- Discrete Coils/Flags
Random - simulate flag randomly
Toggle - simulate flag on/off periodicaly
- Registers
Random - simulate register randomly
Increment - simulate register from Low Limit to High Limit with a given Step
Decrement - simulate register from High Limit to Low Limit with a given Step
- Modbus Message Parser
- Modbus Definitions
- Error Simualtions
From version 1.2.0 Open ModSim supports scripting. Qt runtime implements the ECMAScript Language Specification standard, so Javascript is used to write code.
Scripts can be launched in two modes: Once or Periodically. If you run script in Once mode the script will stop after it finishes executing. In Periodically mode, the script will start after a certain period of time until the user stops it or the method is called
Script.stop();Here is an example of using the script in the Periodically mode
/**************************************************************************/
/*
/* Example script that store value after 3 seconds
/*
***************************************************************************/
/* Set the server address base starts from one (1-based) */
Server.addressBase = AddressBase.Base1;
let deviceId = 1;
let address1 = 1;
let address10 = 10;
function reset()
{
/* Write to a Holding register at address1 zero value */
Server.writeHolding(address1, 0, deviceId);
}
/* init function */
function init()
{
reset();
/* Print server error if occured and stop script execution */
Server.onError(deviceId, (error)=> {
console.error(error);
Script.stop();
});
/* Runs when Hodling register value at address1 was changed */
Server.onChange(deviceId, Register.Holding, address1, (value)=>
{
if(value === 1)
{
/* Runs after 3 seconds and increase Holding register value at address10
* Then reset register value at address1 and stop script execution
*/
Script.setTimeout(function()
{
Server.writeHolding(address10, Server.readHolding(address10, deviceId) + 1, deviceId);
reset();
Script.stop();
}, 3000);
}
});
}
/* Runs once when script started */
Script.onInit(init);The following minimum operating system versions are supported for OpenModSim:
Microsoft Windows 7
macOS 15 (Sequoia)
Debian Linux 11
Ubuntu Linux 22.04
Mint Linux 22
Zorin OS 18
Fedora Linux 41
Rocky Linux 9.7
OpenSuse Linux 15.6
Alt Linux 11
Astra Linux 1.7
RedOS 8
Arch (manual building only)
Building is available via cmake (with installed Qt version 5.15 and above) or Qt Creator. Supports both OS Microsoft Windows and Linux.
Note
Building from source requires CMake version 3.28.4 or newer.
The minimum supported version of Microsoft Windows for building OpenModSim from sources is Windows 10.
- Install latest git version
- Run Windows PowerShell terminal as an Administrator
- Clone OpenModSim sources from github repository
git clone https://github.com/sanny32/OpenModSim.git- Go to OpenModSim folder
cd OpenModSim- Allow script execution in PowerShell terminal
Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass- Run the build script
.\build.ps1If you need to specify Qt framework major version (5 or 6), you can do it in the parameters
.\build.ps1 -qt5or.\build.ps1 -qt6
To enable the experimental Qlementine application style (requires Qt6 >= 6.8):
.\build.ps1 -qlementine
The build script supports building the application only for 64-bit architecture.
- Install git for your Linux distribution
- Run the following commands from the console:
git clone https://github.com/sanny32/OpenModSim.gitcd OpenModSim./build.shIf you need to specify Qt framework major version (5 or 6), you can do it in the parameters
./build.sh -qt5or./build.sh -qt6
To enable the experimental Qlementine application style (requires Qt6 >= 6.8):
./build.sh -qlementine
The minimum supported version of macOS for building OpenModSim from sources is macOS 11 (Big Sur).
- Install Homebrew if not already installed
- Install required dependencies:
brew install qt@6 cmake ninja- Clone OpenModSim sources from github repository:
git clone https://github.com/sanny32/OpenModSim.git- Go to OpenModSim folder:
cd OpenModSim- Run the build script:
./build-macos.shNote
On macOS, OpenModSim uses Qlementine style and Qlementine Icons by default when building with Qt6 >= 6.8. These dependencies are fetched automatically during CMake configure and improve icon/theme consistency on macOS. If you build with Qt5 or Qt6 < 6.8, OpenModSim falls back to the standard built-in style.
The build script generates a macOS application bundle (omodsim.app). To run the application:
open build-omodsim-Qt_*/omodsim.appInstall from binary distributions
Below are the methods for installing the OpenModSim for different OS
Run the installer:
- For 32-bit Windows:
qt5-omodsim2-2.0.0-beta1_x86.exe - For 64-bit Windows:
qt5-omodsim2-2.0.0-beta1_x64.exeorqt6-omodsim2-2.0.0-beta1_x64.exe
Open the DMG package:
open qt6-omodsim2-2.0.0-beta1_arm64.dmgThen drag Open ModSim 2.app to the Applications folder.
Before the first launch, allow the application to run in System Settings > Privacy & Security, or remove the quarantine attribute from the command line:
xattr -dr com.apple.quarantine "/Applications/Open ModSim 2.app"Run the application:
open "/Applications/Open ModSim 2.app"To remove the application, move it to Trash or run:
rm -rf "/Applications/Open ModSim 2.app"Install the DEB package from the command line:
sudo apt install ./qt6-omodsim2_2.0.0-beta1-1_amd64.debor if you want to use Qt5 libraries:
sudo apt install ./qt5-omodsim2_2.0.0-beta1-1_amd64.debTo remove the DEB package run:
sudo apt remove qt6-omodsim2or for Qt5 package:
sudo apt remove qt5-omodsim2
Install the RPM package from the command line:
sudo dnf install ./qt6-omodsim2-2.0.0-beta1-1.x86_64.rpmTo remove the RPM package run:
sudo dnf remove qt6-omodsim2Install the RPM package from the command line as root user:
apt-get install ./qt6-omodsim2-2.0.0-beta1-1.x86_64.rpmTo remove the RPM package run as root user:
apt-get remove qt6-omodsim2
Import qt6-omodsim2.rpm.pubkey to rpm repository:
sudo rpm --import qt6-omodsim2.rpm.pubkeyInstall the RPM package using Zypper:
sudo zypper install ./qt6-omodsim2-2.0.0-beta1-1.x86_64.rpmTo remove the RPM package run:
sudo zypper remove qt6-omodsim2Windows binaries for this project are signed thanks to SignPath Foundation.
- 🔐 Free code signing service: SignPath.io
- 📜 Certificate provider: SignPath Foundation
Copyright 2023-2026 Alexandr Ananev [mail@ananev.org]
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