Poll any Modbus TCP or RTU slave device. Read and write registers, monitor real-time responses, and debug communication issues — all in one Windows application.
No registration · No credit card · Master + Slave included · Windows 10/11
In Modbus protocol, the master (or client in TCP terminology) is the device that initiates all communication. It sends requests — "read holding registers 40001–40010 from device ID 3" — and the slave responds with data. There is always exactly one master per Modbus RTU bus; TCP allows multiple concurrent masters.
Engineers use a Modbus master simulator to test real slave devices — PLCs, energy meters, VFD drives, temperature controllers — during commissioning, integration, and troubleshooting. Instead of writing custom code, you open the simulator, point it at the device, and read/write registers in minutes.
Connect to any Modbus TCP slave by IP address and port. Multiple simultaneous TCP connections. Configurable timeout and retry count. Works over LAN, VPN, or localhost.
Connect to RTU slaves over physical COM ports or virtual COM port pairs. Configurable baud rate (1200–115200), parity, data bits, stop bits. Supports all standard RS-485 topologies.
Continuously poll Holding Registers, Coils, Input Registers, and Discrete Inputs. Configurable scan interval (100ms to 60s). Color-coded display — values update in real time.
Write single register (FC06), multiple registers (FC16), single coil (FC05), multiple coils (FC15). Enter values as decimal, hex, float, or binary. Write on demand or on a timer.
View 32-bit values spanning two registers. Choose byte order per register block: Big Endian (ABCD), Little Endian (DCBA), Mid-Big (BADC), Mid-Little (CDAB). Essential for energy meters and drives.
See every request and response: function code, register address, raw bytes, response time, error codes. Export log to CSV. Timestamps in milliseconds. Invaluable for debugging timeout and framing issues.
Save your master connection settings, register scan ranges, and data type mappings to a file. Reload instantly for the next session. Share with your team so everyone uses the same configuration.
| FC | Name | Register Type | Read/Write | Max Count |
|---|---|---|---|---|
| 01 | Read Coils | Coils (0x) | Read | 2,000 bits |
| 02 | Read Discrete Inputs | Discrete Inputs (1x) | Read | 2,000 bits |
| 03 | Read Holding Registers | Holding Registers (4x) | Read | 125 registers |
| 04 | Read Input Registers | Input Registers (3x) | Read | 125 registers |
| 05 | Write Single Coil | Coils (0x) | Write | 1 coil |
| 06 | Write Single Register | Holding Registers (4x) | Write | 1 register |
| 15 | Write Multiple Coils | Coils (0x) | Write | 1,968 bits |
| 16 | Write Multiple Registers | Holding Registers (4x) | Write | 123 registers |
Modbus Poll (master only) costs $65. Modbus Slave costs another $65. That's $130 for separate tools. ModbusSimulator.com gives you Master and Slave in one $59 license — and they share the same UI so you can run a master scan while simultaneously running a slave server.
The master initiates all communication — it sends requests for data. The slave responds to those requests with register values. A real PLC, energy meter, or VFD is usually the slave. You use a master simulator to talk to those devices. ModbusSimulator.com can act as both master (to test a real slave) and slave (to test a real master, like a SCADA system).
Yes. Use FC06 to write a single holding register or FC16 to write multiple registers in one request. Enter the target register address, value, and data type (INT16, UINT16, FLOAT32, etc.). The PLC must have its Modbus slave configured to accept writes on those addresses.
Select Modbus TCP mode, enter the device's IP address and port (default: 502), and set the Unit ID (slave address, usually 1 or 255 for TCP). Click Connect. The master will immediately show the connection status and you can start scanning registers.
ModbusSimulator.com supports poll intervals from 100ms to 60,000ms (1 minute). The practical minimum is limited by the device's response time — most Modbus devices respond within 50–200ms. Setting interval too low causes timeouts if the device can't keep up.
Master + Slave · TCP + RTU + ASCII · Windows 10/11 · One-time $59