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1.3  Simulate Modbus RTU Device

This will explain how to setup SimServe to act as a single Modbus RTU slave device with default settings. In just a few minutes, SimServe will be ready to simulate a modbus slave device for any Modbus master like a SCADA system or PLC. To setup the simulation, follow the steps below.

  1. Launch the SimServe web interface, and click on "New Network Item" in the network tree.

  2. Fill out the "New Network Item" form as described below and click save.


    Enter any preferred name

    Network Item Type

    Select "Device"


    Select "MBRTU"

    RS Protocol

    Enter the RS protocol that’s used by the real device. Most common is RS232 or RS485.

    COM Port

    Enter the name of the COM port that exists on the computer running SimServe.
    To find the name of available com ports on the computer, launch device manager and look under "Ports (COM & LPT)". The com port should be named something like "COM2". Enter "COM2" exactly as shown in the form.

    Baud Rate

    Enter baud rate that’s used by the real device.
    Most devices use 9600 by default.

    Data Bits

    Enter data bits that’s used by the real device.
    Most devices use 8 by default.

    Stop Bits

    Enter stop bits that’s used by the real device.
    Most devices use 1 by default.


    Enter parity that’s used by the real device.
    Most devices use none by default.

    Slave Address

    Enter the slave address that’s used by the real device.

    Remaining Fields

    Leave as default.


  3. The Modbus slave device will appear under the network tree. Double click the device to access it’s memory.

  4. By default, the device is configured with every possible modbus register and it’s value can be modified by simply typing a new number in the value field. The value of each binary bit for the register is displayed as well, and clicking on the bit toggle’s it’s value.
  5. SimServe is now actively simulating the modbus device and will respond to requests from a Modbus master. Configure your Modbus master with the appropriate communication settings to connect with the device. For most Modbus masters, you’ll need to enter the RS protocol, baud rate, data bits, stop bits, parity, and slave address that you assigned to the slave device in step 2. You may poll the Modbus slave device for any valid Modbus register.