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
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
/*
***************************************************************************/
function clear()
{
/* Write to a Holding register at address 1 zero value */
Server.writeHolding(1, 0);
}
/* init function */
function init()
{
/* Set the server address base starts from one (1-based) */
Server.addressBase = AddressBase.Base1;
clear();
/* Runs when Hodling register value at address 1 was changed */
Server.onChange(Register.Holding, 1, (value)=>
{
if(value === 1)
{
/* Runs after 3 seconds and increase Holding register value at address 10
* Then stop script execution
*/
Script.setTimeout(function()
{
Server.writeHolding(10, Server.readHolding(10) + 1);
Script.stop();
}, 3000);
}
});
}
/* Runs once when script started */
Script.onInit(init);Now building is available via cmake (with installed Qt version 5.15 and above) or Qt Creator. Supports both OS Microsoft Windows and Linux.
The following minimum operating system versions are supported for OpenModSim:
- Microsoft Windows 7
- Debian Linux 11
- Ubuntu Linux 22.04
- Mint Linux 22
- Fedora Linux 41
- OpenSuse Linux 15.6
- Alt Linux 11
- Astra Linux 1.7
- RedOS 8
Below are the methods for installing the OpenModSim for different OS
Run the installer:
- For 32-bit Windows:
qt5-omodsim_1.9.0-1_x86.exe - For 64-bit Windows:
qt5-omodsim_1.9.0-1_amd64.exeorqt6-omodsim_1.9.0-1_amd64.exe
Install the DEB package from the command line:
sudo apt install -f ./qt6-omodsim_1.9.0-1_amd64.debor if you want to use Qt5 libraries:
sudo apt install -f ./qt5-omodsim_1.9.0-1_amd64.debTo remove the DEB package run:
sudo apt remove qt6-omodsimor for Qt5 package:
sudo apt remove qt5-omodsimInstall the RPM package from the command line:
sudo dnf install ./qt6-omodsim_1.9.0-1.x86_64.rpmTo remove the RPM package run:
sudo dnf remove qt6-omodsimInstall the RPM package from the command line as root user:
apt-get install ./qt6-omodsim_1.9.0-1.x86_64.rpmTo remove the RPM package run as root user:
apt-get remove qt6-omodsimImport qt6-omodsim.rpm.pubkey to rpm repository:
sudo rpm --import qt6-omodsim.rpm.pubkeyInstall the RPM package using Zypper:
sudo zypper install ./qt6-omodsim_1.9.0-1.x86_64.rpmTo remove the RPM package run:
sudo zypper remove qt6-omodsimCopyright 2025 Alexandr Ananev [mail@ananev.org]
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
