Acquire Modbus Slave data over Modbus TCP

1. Objective

Simulate a Modbus TCP slave with Modbus Slave. Acquire its data using Modbus Client (Master), process it, and display results in real time.

2. Simulator, device, and plugins

• Simulator

Modbus Slave simulates slave devices, receiving master command packets and returning data packets.

Connection and point settings:

key	name
Protocol (Connection)	Modbus TCP/IP
IP address	0.0.0.0
Port	502
Slave ID	1
Register type	Holding Registers
Data type	Unsigned

• Device

  RSB-3720

• Plugins

  Modbus Client (Master), Data Processing, and MQTT Upload

3. Rules

(1) Simulate three points in Modbus Slave.

- Protocol: Modbus TCP.
- Register type: Holding Register.
- Data type: uint16.
- Byte order: big-endian (AB).
- Point addresses: 0, 1, and 2.

(2) Acquire three Modbus points over TCP as X, Y, and Z, using formulas {X}/10, {Y}**3, and {Z}*3.1412, respectively.

(3) The resulting connection scheme is:

4. Key steps

(1) Configure Modbus Slave.

1). Select Modbus Slave → File → New to create an Mbslave.

• No Connection: no connected device.
• ID=1: slave ID 1, configurable.
• F=3: Function 03 Holding Registers (4x), matching the acquisition plugin’s register type.
• Numbers 0–7 on the left are data addresses.

2). Select Connection → Connect…, enter parameters, and select OK.

• Connection: Modbus TCP/IP.
• IP Address: simulated device IP, default 0.0.0.0. In the acquisition plugin, use the actual IP of the PC running the simulator.
• Port: simulated device port, default 502.

3). Select SetUp → Slave Definition…, enter parameters, and select OK.

• Slave ID: slave address ID, default 1.
• Function: 03 Holding Register (4x).
• Address: 0.
• Quantity: 3 registers.

4). Select the three points, then Display → Unsigned.

5). Double-click the first row, enter value 88, and select OK.

6). Set the second and third points to 12 and 35.

(2) Configure acquisition in Modbus Client (Master).

1). Connection settings. Scheme name is required.

Match the simulator parameters:

• Scheme name: Slave acquisition
• Protocol: Modbus TCP
• Synchronous acquisition: Yes
• Acquisition interval (ms): 1000
• Timeout: 500
• Data freshness (ms): 500

2). Add a group.

Select Add group, enter these values, and select Finish:

• Group name: Group 1
• Slave ID: 1
• IP: 172.21.78.157
• Port: 502

Note: IP, port, and Slave ID must match the simulator; the IP is the address of the computer running it.

3). Add points.

Select Add data, enter these values, and confirm:

• Data alias: X
• Address: 0
• Register type: Holding Registers
• Data type: uint16
• Register count: 1
• Byte order: AB
• Read/write mode: r
• Calculation: {X}/10

5. Results

(1) Select Deploy under Device Connectivity and wait for success.

(2) Switch to Digital Twin, hover over Modbus Client (Master), select Slave acquisition, and view acquired real-time data.

(3) Hover over Data Processing, select Slave acquisition, and view processed real-time data.