Development overview and development direction of programmable controller PLC
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How have PLCs developed, and where are they heading?
Four tracks tell the story. Hardware: from the first relay-replacement controller in the late 1960s, through microprocessor-based units in the 1980s, to today's multi-core controllers that can also host edge applications. Software: from ladder-only, through the IEC 61131-3 standardisation of the 1990s, to version-controlled, multi-language engineering. Communication: from proprietary serial networks, through industrial Ethernet, to OPC UA and MQTT. Integration: from standalone cabinets to IIoT-connected edge nodes. The direction continues along the same lines: more edge computing now, growing AI assistance in engineering and analytics, and digital-twin workflows maturing over the next few years.
An earlier version of this page carried an attributed engineer quote and forecast timelines stated as fact. The quote could not be verified and has been removed; the forward-looking sections below are framed as directions, not dates.
The development timeline
| Era | Character |
|---|---|
| Late 1960s-1970s | Relay replacement. The first programmable controllers answered the automotive industry's need to change control logic without rewiring; memory was scarce and logic was simple. |
| 1980s-1990s | Microprocessors and networks. Processors moved in, capacities grew, and proprietary serial networks connected controllers to supervisory systems. |
| 2000s-2010s | Standardisation and Ethernet. The IEC 61131-3 languages spread, industrial Ethernet displaced proprietary fieldbus in new builds, and HMI integration became routine. |
| 2020s | IIoT and edge. Cloud integration, standardised data exchange (OPC UA, MQTT), edge computing on the controller, and security standards reshaping procurement. |
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Future directions
| Direction | Status |
|---|---|
| Edge computing on the controller | Here now: current mid-range and flagship CPUs host analytics and pre-processing alongside control |
| AI assistance in engineering and analytics | Arriving: code-assist features in engineering tools, anomaly detection moving onto controllers |
| Digital-twin workflows | Maturing: simulation-coupled commissioning is established at the high end and spreading downward |
| 5G and wireless convergence | Exploratory to early adoption for specific mobile and flexible-factory use cases |
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Every one of these directions builds on the same foundation rather than replacing it. The controller stays deterministic; the new capabilities attach around it. That is also why each era's predictions of the PLC's demise have been wrong: the deterministic, rugged control layer is the part that does not go away.
What skills hold up
The durable skills are the old ones: logic, timing, I/O, networking fundamentals and disciplined documentation. The additions layer on top: industrial network security practice, data-exchange conventions (OPC UA information models, MQTT payloads), and enough IT literacy to work alongside plant IT rather than around it. Engineers who learn the fundamentals properly find each new wave cheaper to absorb; engineers who chase features over fundamentals re-learn every cycle.
Example: the same relay-replacement logic, three eras
A motor start-stop with interlock was the bread-and-butter program of the 1970s relay panel, the first ladder exercise of the 1990s PLC course, and still the first exercise on a current controller with its edge runtime in the background. The wrapper changed three times; the logic and the discipline behind it never did. Learn the fundamentals well and the future directions are upgrades, not restarts.
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