A standard C99-based middleware designed on the ANSYS SCADE Display platform, enabling HMI screens to communicate with field-level HIMA HiMatrix F35 safety PLCs via Modbus TCP/IP.

Scope: An integration application operating on the zero-copy principle, developed to establish data exchange between SCADE’s closed-loop structure and the control layer.

Project Portfolio

Current Situation and Problem

Context: The necessity to migrate the interlocking simulation system (4 tracks, 6 signals, 1 switch) at the ITU Railway Systems Laboratory to a SCADE Display-supported HMI architecture compliant with industrial and certifiable standards. Critical Issues: The absence of a native Modbus interface within SCADE Display and the platform’s closed-network design. The inability of the HMI interface to communicate directly with actual field controllers (HIMA HiMatrix F35), and the lack of dynamic field configuration for IP/port maps.

Solution Architecture and Execution

Architectural Approach

Architectural Constraint Assessment: The generated SCADE application used in this setup provided no native Modbus interface. An external C middleware layer was therefore developed to exchange data with the HIMA controller while keeping the HMI logic separate from the communication layer. This is consistent with EN 50128 practice for separating application logic from communication.

A C99 middleware wrapper layer was designed between SCADE’s generated code and the libmodbus library:

Communication Flow

Applied Methodology

• Zero-Copy Integration: Copy overhead was eliminated by hooking directly into the SCADE main loop.
• Dynamic Configuration: A 3-region INI file was used to prevent recompilation requirements during field deployment.

Fallback behaviour: If the configuration file is missing or invalid, the PoC writes a local default configuration for laboratory use. A production implementation should fail safely or require explicit operator confirmation.

• Auto-Reconnection: Connection drops in industrial environments are inevitable; an autonomous auto-reconnect cycle was activated.
• Change Detection: A batch read and selective write strategy was implemented to optimize network traffic.

Architectural Decision: Since HMI hardware’s capability for simultaneous physical command processing is limited, outputs are evaluated in a sequential loop. This structural preference prevents unnecessary fieldbus traffic (network flooding).

• Thread-Safe Logging: Every event in critical systems must be logged securely.

Interlocking Scope

Example route: RT01: SN01E → TC01 → TC04 → TC02 → SN02E (Switch: Normal)

Safety Rule: Based on critical design principles, all signals not explicitly demanded by the system are configured to default to a restrictive state (red).

Results and Operational Takeaways

Quantitative Gain: (Potential values obtained during laboratory PoC tests)

Project Visuals

Related Links

 Source Code: Github/ansys-scade-modbus-integration-middleware 
Download TOK 2025 Paper: SCADE Modbus Paper Turkish (PDF)

Authors: Dora Demir¹, İbrahim Can Kolotoğlu², Muhammet Işık², Serhat Boynukalın³, Mehmet Turan Söylemez²
¹ ITU Electronics and Communication Eng. | ² ITU Control and Automation Eng. | ³ ITU Graduate School

This work was conducted at the ITU EEF Railway Systems Laboratory and published at the Turkish Automatic Control 2025 (TOK 2025) conference.