This article explains how the IEC 61131 PLC environments and Juliet & Romeo® relate to each other, outlining their similarities, differences, and how to decide which to use for specific tasks. When comparing Juliet & Romeo® and the IEC 61131 PLC environments, the question isn’t which one replaces the other; it’s how they complement each other.
IEC 61131 is a mature, stable international standard for programmable logic controllers (PLCs). It works well for traditional industrial automation, discrete logic, safety, etc.In particular, IEC 61131-3 defines multiple programming languages: graphical (Ladder Diagram (LD), Function Block Diagram (FBD)), textual (Structured Text (ST)), Sequential Function Chart (SFC), etc. With CODESYS as the leading manufacturer-independent IEC 61131-3 Software Suite, users and developers have access to well established tools for development of periodically executed application programs.
Juliet & Romeo is designed specifically for modern automation and motion programming, also for flexible muti system applications. For this, real-time guarantees and safe, deterministic behaviors are a must. At the same time, to be able to write all sorts of components (sensor data processing, communication protocols, coordinated motion programs, process logic, AI, etc.), it comes with modern software concepts, an expressive language (Juliet) and libraries for code modeling and meta programming. This together with event driven execution, simplifies implementation and maintenance of more complex applications. Juliet & Romeo has functionality to emulate a PLC runtime, with libraries allowing quick implementation of periodically executed tasks. But it can just as well run in parallel to CODESYS and integrate through libraries that allow Juliet programs to exchange data with the CODESYS runtime.
Using an IEC 61131 language is an excellent choice for sequential logic and simple periodic tasks. Applications implemented in one of the IEC 61131 languages, can easily be extended with new functionality or logic written in Juliet. This protects previous investments without compromising adaptability. Applications written in Juliet are mostly easier to maintain and keep track of due to the unified language that even higher-level code modeling and advanced algorithms can be efficiently expressed in. All while keeping low latency for instant reactiveness. With Juliet & Romeo, adaptations do not need to be costly headaches.
Juliet & Romeo
Juliet is an expressive robotics & automation programming language: real-time, multitasking, with robustness features and automatic memory management.
Romeo is a real-time virtual machine/runtime that executes Juliet (and any bytecode conforming to its format), designed for deterministic behavior, low latency, responsive to events, sensor feedback, etc.
The goal of Juliet & Romeo is to unify motion control, process logic, sensor handling, AI, UI, etc. in one expressive language/runtime stack; to reduce development overhead, improve consistency, help scale automation systems and make them easier to evolve.
IEC 61131
An international standard for programmable logic controllers (PLCs). In particular, IEC 61131-3 defines programming languages and software architecture for PLCs.
Specifies multiple programming languages: graphical (Ladder Diagram (LD), Function Block Diagram (FBD)), textual (Structured Text (ST)), Sequential Function Chart (SFC), etc. The 2025 edition has updates.
Also covers concepts such as program organization units (POUs), safety, communications, and requirements for hardware, among others.
From the description above, it should be easy to understand that there is no competition between the two technologies. IEC 61131 is a standard, and Juliet & Romeo are a real-time development platform. Most IEC 61131 functionality is or can be supported in Juliet, but Juliet & Romeo also offers great integration possibilities with CODESYS runtime, making Co-existence the obvious choice to extend previous investments with new functionality. For new robotics-heavy automation projects, Juliet & Romeo offer richer functionality; for traditional PLC tasks, IEC 61131 remains very strong.
Here are the key dimensions along which they differ, overlap, or complement each other
For deeper technical insights, the following articles explore how Juliet & Romeo® relates to key automation ecosystems and standards:
Juliet & Romeo® and ROS 2 (link): How Cognibotics’ real-time platform complements the open-source robotics framework.
Juliet & Romeo® and IEC 61131 (link): How modern deterministic automation extends traditional PLC programming environments.
Juliet & Romeo® and SRCI (link): Understanding how standardized PLC-to-robot interfaces align with Cognibotics’ real-time approach.
Julliet & Romeo® Coexisting with Robotics and Automation Ecosystem (link): By coexisting with IEC 61131 PLCs, SRCI, and ROS, it supports modernization where ROI is clear, without disrupting what already works.
