WinCC S7-1200 S7-200SMART Wireless Modbus TCP Configuration

ByHANI_AUTOMATION HANI

In many industrial environments, running cables between control rooms and field PLCs is costly or impractical. This article presents a proven method for establishing wireless Modbus TCP communication between a WinCC SCADA system and Siemens S7-1200 and S7-200SMART PLCs. The solution uses dedicated wireless Ethernet terminals that require no changes to the existing PLC program, making it a drop-in upgrade for existing installations.

System Overview and Hardware Requirements

The test setup consists of one master station (WinCC) and two slave PLCs: an S7-1200 and an S7-200SMART. Three wireless communication terminals act as transparent bridges, converting wired Ethernet to a robust wireless link. The key hardware parameters are:

Component Specification
Master PLC Siemens S7-1200 (1 unit)
Slave PLC Siemens S7-200SMART (1 unit)
SCADA WinCC V7.4
Wireless Terminals 3 units, RJ45 interface, 12-24VDC power
Protocol Modbus TCP/IP
Wireless Range Up to 1 km (line-of-sight)

The wireless terminals operate in pairs or groups, creating a transparent wireless Ethernet network. They support Modbus TCP/IP natively, so the PLCs and WinCC communicate exactly as they would over a wired LAN. This approach eliminates the need for complex routing or protocol conversion.

Wiring and Physical Connections

Connecting the devices is straightforward. Each wireless terminal has a standard RJ45 port. Use shielded CAT5e or CAT6 Ethernet cables for best noise immunity.

  • WinCC PC to Wireless Terminal: Connect one end of the Ethernet cable to the PC’s network port and the other to the wireless terminal assigned to the master station.
  • S7-1200 to Wireless Terminal: Plug the cable into the PLC’s PROFINET port and the corresponding wireless terminal.
  • S7-200SMART to Wireless Terminal: Similarly, connect the PLC’s Ethernet port to its dedicated wireless terminal.

Power each wireless terminal with 12-24VDC. Ensure all devices are on the same IP subnet (e.g., 192.168.2.x) to allow seamless communication. The wireless terminals do not require any IP configuration; they simply forward Ethernet frames.

Configuring WinCC for Modbus TCP Communication

WinCC uses the Modbus TCP/IP channel for communication. Follow these steps to set up the connection to both PLCs:

  1. Open the WinCC project and navigate to Tag Management.
  2. Add a new driver: right-click on Tag Management, select Add New Driver, and choose Modbus TCP/IP.
  3. Under the new driver, create two connections (one for each PLC). Right-click on the driver unit and select New Connection.
  4. For each connection, set the PLC’s IP address. For example, set the S7-1200 to 192.168.2.11 and the S7-200SMART to 192.168.2.12. The IP addresses must be unique and within the same subnet.
  5. Create tags (variables) for each data point you want to monitor or control. Specify the Modbus address (e.g., holding register 40001 for Q0.0, discrete input 10001 for I0.0). Ensure the data types match the PLC program.

Design the graphical interface by adding buttons and indicators. Link each button to a tag (e.g., a start button writes to a coil, a stop button writes to another coil). Use I/O fields to display analog values from holding registers.

PLC Program and IP Settings

The PLCs must be configured as Modbus TCP servers (slaves). In TIA Portal for the S7-1200, enable the Modbus TCP server function in the device configuration. For the S7-200SMART, use the Modbus TCP library in STEP 7-Micro/WIN SMART.

A simple start/stop logic can be implemented using coils Q0.2 and Q0.3. The PLC program should map these coils to Modbus addresses. For example:


Network 1: LD I0.0 // Start button
              O Q0.2
              AN I0.1 // Stop button
              = Q0.2
Network 2: LD I0.2
              O Q0.3
              AN I0.3
              = Q0.3

Set the IP address of each PLC in the device configuration. For the S7-1200, go to Device & Networks and assign a static IP. For the S7-200SMART, use the Communications dialog. Download the program to each PLC via Ethernet.

Testing and Commissioning

After configuration, verify the wireless communication with these tests:

Test Procedure Expected Result
Digital Output Control Use WinCC buttons to toggle Q0.2 and Q0.3 Corresponding PLC outputs turn on/off; status updates in WinCC
Digital Input Monitoring Apply 24V to PLC inputs I0.0, I0.1, etc. WinCC indicators reflect the input states in real time
Analog Value Read/Write Write a value to a holding register (e.g., MW10) from WinCC The value appears in the PLC and can be read back

Monitor the wireless link quality using diagnostic LEDs on the terminals. A solid link light indicates a stable connection. If communication is intermittent, check antenna placement, power supply stability, and potential sources of interference.

Benefits and Practical Considerations

This wireless Modbus TCP solution offers several advantages for industrial automation:

  • Cost Savings: Eliminates expensive cable trenches, conduits, and labor for long-distance runs.
  • Flexibility: Easily relocate PLCs or add new nodes without rewiring.
  • Reliability: Modern wireless terminals use frequency-hopping and error correction to maintain robust links even in noisy industrial environments.
  • Transparency: No changes to the PLC program or SCADA configuration are needed beyond IP addressing.
  • Scalability: The same architecture can support multiple PLCs by adding more wireless terminals.

When deploying such a system, ensure that the wireless terminals are approved for your region (FCC, CE, etc.) and that the operating frequency does not conflict with existing wireless infrastructure. For critical applications, consider redundant wireless paths or a hybrid wired/wireless design.

Note: Always perform a site survey to assess RF conditions before final installation. Metal structures, large motors, and variable frequency drives can affect wireless performance. Proper antenna placement and grounding are essential for reliable operation.

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