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OpenPLC Integration

Overview

OpenPLC is an open-source Programmable Logic Controller (PLC) that serves as the control system in the CybICS testbed. It reads sensor data from the physical process (real or simulated) and controls actuators based on the programmed control logic. The OpenPLC provides a web-based interface for programming, monitoring, and debugging the control system.

Purpose

In the CybICS testbed, OpenPLC serves several critical functions:

  1. Process Control: Implements the automatic control logic for the gas pressure system
  2. Manual Override: Allows operators to manually control valves and compressors
  3. Training Platform: Provides a realistic ICS environment for cybersecurity training
  4. Protocol Support: Supports multiple industrial protocols (Modbus TCP, DNP3, EtherNet/IP, S7)
  5. Vulnerability Target: Serves as a target for security testing and penetration exercises

Architecture

Communication Protocols

OpenPLC in CybICS is configured to support multiple industrial protocols:

  • Modbus TCP (Port 502): Primary communication protocol
  • DNP3 (Port 20000): Distributed Network Protocol for SCADA
  • EtherNet/IP (Port 44818): Industrial Ethernet protocol
  • S7comm (Port 102): Siemens S7 protocol
  • HTTP (Port 8080): Web interface for programming and monitoring

Default Configuration

Web Interface Access

  • URL: http://<device-ip>:8080
  • Default Credentials:

Pre-installed Program

The CybICS OpenPLC comes with a pre-installed control program (cybICS.st) that implements:

  • Automatic Control Mode: Maintains GST between 60-240 bar and HPT between 60-90 bar
  • Manual Control Mode: Allows operator to manually control compressor and valves
  • Safety Interlocks: Prevents compressor operation when GST is too low
  • Heartbeat: Visual indicator that the PLC is running
  • Emergency Stop: System stop functionality

I/O Mapping

Input Registers (Sensors)

Address Variable Description Range
%MW100 gst Gas Storage Tank pressure 0-255 bar
%MW102 hpt High Pressure Tank pressure 0-255 bar
%MW104 stop Emergency stop flag 0=run, 1=stop
%MW106 manual Manual mode flag 0=auto, 1=manual
%MW108 systemSen System sensor state Boolean
%MW110 boSen Blowout sensor state Boolean

Modbus Register Mapping:

  • Register 1124: GST pressure (written by hwio)
  • Register 1126: HPT pressure (written by hwio)

Output Coils (Actuators)

Address Variable Description Control
%QX0.0 heartbeat System alive indicator Auto (PLC)
%QX0.1 compressor Compressor control Auto/Manual
%QX0.2 systemValve System valve control Auto/Manual
%QX0.3 gstSig GST fill signal Auto/Manual

Usage

Accessing the Web Interface

  1. Open a web browser
  2. Navigate to http://<device-ip>:8080

Programming the PLC

Uploading a New Program

  1. Click "Programs" in the navigation menu
  2. Click "Upload Program"
  3. Select your .st (Structured Text) file
  4. Click "Upload"
  5. Click "Compile" to build the program
  6. Click "Start PLC" to run

Monitoring Values

  1. Click "Monitoring" in the navigation menu
  2. Select the location to monitor (e.g., %MW100 for GST)
  3. View real-time values and graphs

Troubleshooting

Cannot Access Web Interface

Symptom: Browser shows "Connection refused" or timeout

Solutions:

  1. Verify OpenPLC container is running: 
    docker ps | grep openplc
# or
sudo systemctl status openplc
  2. Check if port 8080 is accessible: 
    curl http://localhost:8080
  3. Verify firewall allows port 8080: 
    sudo iptables -L -n | grep 8080
  4. Check OpenPLC logs: 
    docker logs openplc
# or
sudo journalctl -u openplc -n 50

PLC Program Won't Compile

Symptom: Compilation errors when uploading program

Solutions:

  1. Check syntax of Structured Text program
  2. Verify all variable declarations are correct
  3. Review compilation logs in the web interface
  4. Ensure no special characters in variable names
  5. Try uploading a simple test program to verify compiler works

Modbus Connection Fails

Symptom: hwio cannot connect to OpenPLC via Modbus

Solutions:

  1. Verify Modbus TCP is enabled in Settings → Slave Devices
  2. Check port 502 is exposed: 
    netstat -tuln | grep 502
# or
ss -tuln | grep 502
  3. Test Modbus connection: 
    from pymodbus.client import ModbusTcpClient
c = ModbusTcpClient('localhost', 502)
c.connect()
print(c.connected)  # Should be True
  4. Review OpenPLC runtime logs
  5. Restart OpenPLC service

PLC Not Reading Sensor Values

Symptom: Input registers show 0 or don't update

Solutions:

  1. Verify hwio-raspberry or hwio-virtual is running and connected
  2. Check Modbus register mapping (1124 → %MW100, 1126 → %MW102)
  3. Use Modbus client to verify values are being written: 
    from pymodbus.client import ModbusTcpClient
c = ModbusTcpClient('localhost', 502)
c.connect()
print(c.read_holding_registers(1124, 2))  # Should show GST and HPT
  4. Verify PLC is in RUN mode (not STOP)
  5. Check for program logic errors

Actuators Not Responding

Symptom: Physical LEDs or simulated process doesn't respond to PLC outputs

Solutions:

  1. Verify PLC outputs are changing in Monitoring view
  2. Check hwio service is reading from OpenPLC coils
  3. Verify Modbus coil addresses are correct (512, 513, 514, 515)
  4. Test coil reading: 
    from pymodbus.client import ModbusTcpClient
c = ModbusTcpClient('localhost', 502)
c.connect()
print(c.read_coils(512, 4))  # Should show actuator states
  5. Review control logic in PLC program

Advanced Configuration

Changing Scan Cycle Time

Default: 100ms (10 Hz)

Modify in Settings → Hardware → Scan Cycle Time

For faster control: 50ms For less CPU usage: 200ms

Related Documentation