PPI to Ethernet Module Configuration for Siemens PLC and HMI

In modern food production facilities, reliable and fast communication between PLCs and HMIs is critical for maintaining product quality and minimizing downtime. A common challenge arises when using legacy Siemens S7-200 SMART PLCs that lack an integrated Ethernet port. This article presents a practical configuration case using a PPI to Ethernet module to connect a Siemens S7-200 SMART CPU SR40 with a TP900 Comfort HMI, enabling high-speed data exchange and multi-master access.

Project Background and Challenges

A bakery production line with two continuous 24-hour baking lines, each producing 120,000 bags of bread daily, relied on 12 Siemens S7-200 SMART CPU SR40 controllers. These PLCs managed six key stages: ingredient dosing, dough mixing, fermentation, baking, cooling, and packaging. The plant planned to integrate Siemens TP900 Comfort HMIs for local operation and connect to an MES for real-time monitoring of temperature, pressure, and flow data. However, the SR40’s lack of a native Ethernet port forced an initial RS-485 solution, which introduced three major issues:

• Slow communication: At 187.5 kbps, HMI refresh rates exceeded 200 ms, causing curve display lag.
• Single master limitation: RS-485 supports only one master, preventing simultaneous connection of HMI and SCADA.
• Production downtime: Frequent recipe changes required stopping the line to connect programming cables, causing an average of 15 minutes downtime per change, totaling approximately 180,000 CNY annual loss per line.

To overcome these limitations, the team adopted a simple topology: a PPI to Ethernet module connected directly to the PLC’s 9-pin port, with the module’s RJ45 port linked to the HMI. This eliminated the need for additional power supplies and complex wiring.

Equipment List

Hardware Installation Steps

1. Power off: Follow safety protocols by locking out the 24 VDC feeder and verifying the PLC is de-energized.
2. Disconnect existing cables: Remove the old MPI cable from the HMI, labeling wires to avoid confusion.
3. Mount the module: Plug the ETH-S7200-JM02 directly into the PLC’s 9-pin PPI port until it clicks. The module draws power from the PLC port (5 V/80 mA), eliminating external power supplies.
4. Connect Ethernet: Use a shielded CAT5e cable to connect the module’s RJ45 port to the TP900 HMI. For multi-point monitoring, connect through a SCALANCE switch.
5. Grounding: Ensure the module’s metal housing is grounded via the DIN rail to the cabinet’s PE bar, meeting ESD requirements for food environments.
6. Power up: Apply 24 VDC first, then 220 VAC. Check module LEDs: PWR steady green (power OK), LINK steady yellow (Ethernet link up), RX/TX flashing green (data exchange).

Software Configuration

Module Configuration via JM-Tools

1. Launch JM-Tools; it automatically discovers all ETH-S7200-JM02 modules (default IP starts at 192.168.1.200).
2. Modify parameters for each module:
   • IP address: 192.168.0.10 to 192.168.0.21 (matching plant network)
   • Subnet mask: 255.255.255.0
   • Gateway: 192.168.0.1
   • PLC type: S7-200 SMART
   • Serial baud rate: 187.5 kbps (auto-detected, no change needed)
   • Modbus TCP mapping: Holding registers 40001-40064 mapped to VW100-VW226
3. Click “Download” and restart the module to apply settings.

HMI Configuration in WinCC Advanced

1. Create a new connection using the “S7-1200/1500” driver, set the IP to the module’s address (e.g., 192.168.0.10), port 102.
2. Map variables directly to PLC addresses, for example:
   • Fermentation temperature: VW100 → %MW0
   • Baking time: VW102 → %MW1
3. Compile and download to the KTP900. Screen switching time improved from 2 seconds to 200 ms.

PLC Programming

No additional code is needed; the module provides transparent transmission. For remote maintenance, set the remote IP in STEP 7-MicroWIN SMART to the module’s address to enable online monitoring, forcing variables, and firmware updates over Ethernet.

Functional Verification

1. Single-point test: From the control room, ping 192.168.0.10 with latency <1 ms. Write VW100=123 via status table; HMI updates synchronously, confirming zero packet loss.
2. Multi-master test: Simultaneously run WinCC, MES client, and HMI reading VW100-VW120. The module handles queuing without conflicts.
3. 24-hour burn-in: After 3 days of continuous baking, module case temperature stabilized at 45°C with no communication dropouts. During sanitation checks with high-pressure water jets, the module’s IP30 rating and sealing proved adequate.

Key Takeaways and Best Practices

• Ensure the 9-pin connector is fully seated; a loose connection often causes the LINK LED to remain off.
• Use industrial-grade switches (like SCALANCE) to avoid broadcast storms from low-end consumer switches.
• In high-humidity food environments, always use shielded Ethernet cables and protective boots on RJ45 connectors to prevent oxidation.
• For future ERP integration, the module’s MQTT firmware can publish data in JSON format to the cloud, enabling remote recipe push.

Conclusion: By deploying a PPI to Ethernet module, the bakery achieved reliable, high-speed communication between legacy Siemens PLCs and modern HMIs, significantly reducing downtime and enabling seamless integration with higher-level systems. This approach is a cost-effective retrofit for any facility looking to upgrade its automation infrastructure without replacing existing controllers.