Siemens S7-200 to S7-1200 Multi-PLC Logistics Control System Guide

Industry Pain Points and Solutions

In traditional warehouse logistics systems, equipment using Siemens S7-200 PLCs (such as CPU SR20, SR30) often faces three major communication challenges. First, they cannot directly connect to Ethernet networks, forcing multi-PLC data exchange through complex serial cascades with slow response and poor stability. Second, host monitoring systems require dedicated programming cables or serial servers to collect data, adding latency and failure points. Third, connecting different brands of HMIs to the PLC requires custom drivers, leading to compatibility issues and high maintenance costs.

To address these pain points, a large e-commerce warehouse center implemented an automation upgrade using an Ethernet communication processor that connects directly to the S7-200’s PPI port via a 9-pin interface. This module converts serial signals to Ethernet, preserving the original PPI protocol while also supporting Modbus TCP/IP, enabling seamless integration of old and new systems.

Project Background and System Architecture

The e-commerce warehouse covers approximately 5,000 square meters, handling storage and sorting of small to medium-sized items. Before the upgrade, the system consisted of:

• Inbound conveyor line: controlled by Siemens S7-200 CPU SR30, responsible for barcode scanning, weighing, and buffering.
• Automatic sorter: controlled by Siemens S7-1200 CPU 1214C DC/DC/DC, sorting items by destination.
• Outbound conveyor system: controlled by Siemens S7-200 CPU SR20, handling pre-packing transport.
• Monitoring system: developed with KingView 7.5, collecting device data via serial servers.
• Operator terminals: Weinview MT8102iE HMI (inbound area) and Kunlun Tongtai TPC1061Ti HMI (outbound area).

The core requirement was to achieve coordinated control across three zones: when the inbound line detects item information, it must transmit data to the sorter PLC in real time for dynamic sorting strategy adjustment; the outbound system must start corresponding conveyors based on sorting completion signals. Since the original S7-200 PLCs could not communicate directly with the S7-1200 via Ethernet, data exchange relied on manual scheduling, limiting daily throughput to about 8,000 items—far below business growth needs.

After the upgrade, three Ethernet communication modules were installed in the S7-200 control cabinets. These modules connect to the S7-200’s PPI port via a 9-pin D-sub interface and link to the local network through RJ45, enabling:

1. Real-time data exchange between S7-200 and S7-1200 PLCs.
2. Direct Ethernet access for the host PC to all PLC operational data.
3. Continued HMI communication through the module’s 9-pin expansion port without driver changes.

Hardware Configuration and Connection Details

Main Equipment List

Connection Details

S7-200 to Communication Module: The module’s 9-pin female connector links to the S7-200’s PPI port using a standard Siemens PPI cable (6ES7901-3CB30-0XA0). Both devices share a 24V DC power supply to ensure common potential.

Ethernet Network Architecture: All modules’ RJ45 ports connect to the industrial switch via Cat5e cables. The S7-1200’s PROFINET port also connects to the same switch, forming a star topology. The switch links to the IPC via fiber optic transceivers for stable data transmission.

HMI Connection: The Weinview HMI connects to the module’s 9-pin expansion port (the module supports dual serial ports) using an additional PPI cable. The Kunlun Tongtai HMI uses the same method. No driver modifications are needed, preserving original configurations.

Software Configuration and Communication Setup

Module Parameter Configuration

The Ethernet communication processor is configured via a web interface:

1. Log in to the default IP (192.168.1.100), set static IPs (inbound: 192.168.0.10; outbound: 192.168.0.11), subnet mask 255.255.255.0, gateway 192.168.0.1.
2. Set PPI parameters: baud rate 9600 bps, 8 data bits, 1 stop bit, no parity (matching S7-200 defaults).
3. Select “Siemens PPI to Modbus TCP” mode, assign Modbus slave addresses (inbound PLC = 1, outbound PLC = 2).

S7-1200 PLC Programming

Using TIA Portal V16, the S7-1200 program uses the Modbus TCP client function block to communicate with the modules:

1. Call the “MB_CLIENT” block, set server IPs pointing to the two modules.
2. Configure data areas:
   • Read S7-200 I0.0-I0.7 (inbound detection signals) mapped to Modbus addresses 00001-00008.
   • Read S7-200 Q0.0-Q0.7 (device status) mapped to 01001-01008.
   • Write control commands to S7-200 V memory, mapped to holding registers 40001-40010.
3. Implement logic: when inbound detects an item, trigger sorter channel preparation.

S7-200 PLC Program Adjustments

Using STEP 7-Micro/WIN SMART V2.5, modify the original program:

1. Allocate a dedicated data block in V memory (V100.0-V199.9) for data exchange with S7-1200.
2. Add communication status monitoring: if the module link fails, trigger a local alarm (Q1.0 output).
3. Retain original HMI communication logic, using SM0.5 pulse for data refresh.

Host Monitoring System Configuration

In KingView 7.5, add two Modbus TCP devices:

1. Device 1: connect to inbound module (IP 192.168.0.10), read I/Q areas, write commands.
2. Device 2: connect to outbound module (IP 192.168.0.11), same configuration.
3. Create new data screens showing real-time status, faults, and production counts for all three zones.
4. Develop trend charts for hourly throughput, equipment utilization, and other KPIs.

System Commissioning and Performance Results

Key Debugging Steps

1. Communication link test: use the module’s built-in test tool to verify PPI communication, and ping to check Ethernet connectivity.
2. Data read/write test: force output commands in S7-1200 and observe S7-200 response; simulate input signals in S7-200 and confirm S7-1200 reception.
3. HMI compatibility test: operate both Weinview and Kunlun Tongtai HMIs to verify parameter changes and manual controls.
4. Load test: simulate peak conditions (1,500 items per hour) for 8 continuous hours; monitor communication delay (average <50 ms) and packet loss (0%).

Performance Improvements

Summary and Broader Applications

The Ethernet communication module demonstrated three core advantages in this project: it perfectly solved the S7-200’s Ethernet connectivity issue without hardware replacement; its unique dual-serial port design ensured seamless compatibility with existing HMIs, drastically reducing retrofit costs; and its support for both PPI and Modbus protocols provided flexibility for multi-vendor device interconnection.

This solution is not limited to logistics. It can be applied in food processing, packaging machinery, water treatment, and other industrial scenarios using S7-200 series PLCs. Future expansions could include adding cloud gateway modules to upload device data to MES or ERP systems, enabling advanced analytics and remote maintenance, laying the groundwork for Industry 4.0 upgrades.

In industrial automation upgrades, leveraging new technologies to modernize existing assets while protecting prior investments is a common challenge. This case demonstrates how a targeted communication solution can achieve collaboration between old and new systems with minimal modification cost, offering a practical reference for similar projects.