Simulator workflow
Get started with an RTU simulation
A simple first run is: create or open a project, add a simulated device, define its data, configure the COM port and start the bus. A separate Modbus master is needed to send requests to the simulator.
1. Create or open a project
On first launch, the simulator workspace is empty. Choose Add first device to create a test device. Load example devices loads bundled profile examples into the current project. Use Open project to import a JSON project file. The application also keeps the active project in local application storage.
2. Add a device and choose its unit address
Choose a bundled profile or a generic RTU device. Give every enabled simulated unit a distinct address from 1 to 247. Address 0 is reserved for broadcast requests; it is not an address for an individually responding unit. The device settings include a name, description, response delay and response drop percentage.
3. Define the register map
Select a device and open the appropriate data bank: Coils, Discrete Inputs, Input Registers or Holding Registers. Add rows and edit their names and values. The table's Offset is the raw 16-bit PDU address, from 0 through 65535. Coils and discrete inputs represent bits; input and holding register rows store 16-bit values. The simulator marks each row as read-only or writable according to the bank and profile.
Reference labels such as 40001 are not sent directly in a Modbus frame. Use the device map's convention to translate that reference to a PDU offset; see register addressing.
4. Match serial settings
Open Port & RTU, select the COM port and match baud rate, data bits, parity and stop bits to the external master. The dialog also exposes RTS direction, DTR and local-echo handling. Use the timing note in that dialog when checking RTU frame boundaries.
A physical test requires a compatible COM port or USB-to-RS-485 adapter and a separate master such as a PLC, HMI or test program. The adapter provides a physical connection; it does not itself generate Modbus requests.
5. Start the bus and verify traffic
Choose Start bus. The top status shows whether the bus is stopped, starting or running. If opening the COM port fails, check whether another program has it open and verify the port name and adapter driver. The status and error message remain in the application.
Have the external master send a request to one configured unit. Requests, responses and errors appear in the Bus traffic panel with a timestamp and raw bytes. A quiet log means no frame has reached the app; an exception response means the request reached a device but its function or data request needs review.
Save and reuse the project
Use Save project to export the current configuration as JSON. Open project imports a JSON project. New project clears the current simulator setup after a confirmation prompt. Stop simulation before opening a different project.
Optional: scan an existing bus
Scan devices offers Quick, Standard and Thorough modes. The scan sends read-only identification or register requests; it does not write registers. Stop or disconnect every other master before scanning because two masters on one RS-485 bus can collide. Review the result and add detected units deliberately.