Design technology of a PLC industrial control system in 2026: architecture, logi

Detail

Our 2024 post on the design technology of a PLC industrial control system is still a correct introduction for a junior engineer: the three-block structure of input / CPU / output, the ladder-logic programming model, and the Ethernet / Modbus / Profibus protocol choice are all real. What has changed between 2024 and 2026 is the inside of each block. Ladder has been joined by structured text and continuous function chart on every greenfield project, the CPU module is now a multicore SoC with an isolated security core, deterministic Ethernet (PROFINET, EtherNet/IP, CC-Link IE TSN) has displaced PROFIBUS and DeviceNet at the field-bus layer, and cybersecurity has become a first-class design column. This Engineering Note restates the design technology of a PLC industrial control system against a 2026 reference, with a delta against the 2024 version and a sourcing block at the end.

In 2026 a PLC industrial control system still has the three blocks described in 2024: input module, CPU, output module. Inside each block the implementation has changed.

The CPU is now a multicore SoC with a real-time core, an application / gateway core, and an isolated security core. The runtime partition is part of the design statement.

Programming is no longer ladder only. A 2026 design statement should call out ladder, structured text, continuous function chart, and the motion / safety language used for the application.

Communication protocol choice has collapsed to PROFINET, EtherNet/IP, CC-Link IE TSN for greenfield, with Modbus TCP for legacy hand-off. PROFIBUS and DeviceNet are maintenance-only.

Safety and cybersecurity now share the same Ethernet network and an IEC standard family (IEC 61508 / 62061 / 62443-4-2). They are designed together, not as separate deliverables.

The 2024 article described a PLC industrial control system as three blocks: the input module, the central processing unit (CPU), and the output module. The three blocks are still the right way to draw a system on a whiteboard, but the inside of each block has changed.