IEC 61131-3 under RTOS-UH


PLC programming according to the world standard IEC 61131-3 with

  • transparent multitasking, fully preemptive from operating system core to IEC 61131 tasking
  • in combination with CREST-C and PEARL90

offers the Controller Development System CODESYS with the realtime system RTOS-UH.

CODESYS is a complete PLC development environment with a Windows interface. The program development takes place on a PC under Windows.

RTOS-UH provides a stable and proven runtime environment for the soft PLC. The connection to the development system is made conventionally via a serial interface or via a TCP/IP network. Even remote maintenance of target systems via the Internet is seamlessly integrated into the system concept.


All IEC 61131-3 programming languages are supported:

  • IL – Instruction list - as common, elementary language of all IEC 61131-3 compatible controllers
  • CP – coupling plan - for a clear, graphical representation of the elementary links
  • FBD – function block diagram - for visual support during procedural programming
  • ST – structured text - is the new high-level language of the PLC with close relationship to conventional programming languages such as PEARL90 or ANSI-C
  • S/SFC – Sequential Function Chart - expands the programming concept by a clear representation of the program states and state transitions

Program Development

Program development can take place online or offline. A complete offline simulation facilitates the development of critical program parts. Test runs can be carried out stand-alone on the development computer and do not require any system downtime.

Efficiency and comfort during development are our highest priorities for the development system.
The program editors of CODESYS provide:

  • Automatic formatting of program sources
  • Syntactic coloring for marking language elements
  • Seamless integration into the operating concept of the development operating system

Process Control

The integrated debug tools provide complete control and an overview of the program flow even during active operation of the controller:

  • Monitoring allows monitoring of all inputs/outputs as well as internal variables.
  • Forcing, one-time or permanent setting of variables, offers complete system control and enables complete program verification by simulating a wide range of operating conditions.
  • Online program changes allow the modification of the control program without stopping the system.

Program Test

Test runs with direct intervention in the program sequence can be carried out online or offline. The common tools such as

  • Single cycles with control stop after each cycle
  • Breakpoints, control stop when reaching a certain program step
  • Single stepping, i.e. stop of the controller after each program step
  • Sequence control with animation of line states and continuous program tracking
  • Variable watch with storage of previous cycles

provide excellent assistance in evaluating the program flow. In combination with the debug tools an extremely efficient program development is given.

Runtime Support

CODESYS can also be used as an operating, visualization and archiving system. Integrated are

  • Variable trace for tracking and archiving plant data over time
  • Recipe management for setting different operating states of a system
  • graphical visualization for intuitively recognizable representation of the plant status

Finished programs can run as pure runtime systems without CODESYSdevelopment environment independently on the controller. The support of the proven real-time system RTOS-UH remains fully available even in this case.

The combination of a soft PLC with a proven real-time system combines the advantages of both systems:

  • simple and clear programming of the Soft-PLC, combined with the reliable backup of deadlines via the real-time system.
  • fully preemptive tasking – tasks, whether implemented in IEC  61131-3, ANSI-C or PEARL, are processed fully preemptively. Reactivity impairments due to uninterruptible cycle operation or so-called "cooperative" multitasking are avoided.
  • Programming in the state space (AS) ensures the logical transparency of the program flow; the openness of the real-time system ensures compliance with it.

The free choice of the optimal programming tool is given by the seamless integration of IEC 61131-3, ANSI-C and PEARL.
The variety of programming tools makes it possible to choose the most efficient solution for each problem and offers the greatest possible future security in the event of changes in requirements by simple transition to other implementation methods.


CODESYS is available for all RTOS-UH-Targets from embedded MC68k controller to multiprocessor PowerPC. The performance and thus the costs of the controller can be optimally adapted to the requirements.

Connections to all common fieldbus systems are available.

Complete systems in all performance classes are available. IEP offers both standard solutions with guaranteed long-term market availability and customer-specific, optimally cost-oriented implementations.



CoDeSys Brochure



CoDeSys Manual