Program organization units

Within IEC 61131-3, the programs, function blocks, and functions are called program organization units. IEC 61131-3 includes defined standard functions instances, ADD, ABS, SQRT, SIN, and COS. Or, designers can create custom function blocks and reuse those. Function blocks (software objects with increased levels of detailed control) can contain data as well as algorithms. As software objects, these blocks have well-defined interfaces and hidden internals. This creates a clear line between the different program levels — a characteristic that reflects a best practice of object-oriented programming principles.

Function blocks can be written in any of the IEC languages — in most cases, even in C. Programs can also be written using the any of the above-mentioned basic building blocks. Here, sequential function charts control the sequential behavior of a control program and support synchronization and concurrency.

Programming languages

Within IEC 61131-3, the syntax and semantics are defined for five standard programming languages, leaving no room for dialects. This isn't a limitation, because once they're learned, the syntax and semantics can be used on a wide variety of systems based on the IEC 61131-3 standard. Designers are free to choose the programming language based on their knowledge, the problem at hand, external components, interfaces, or even personal preference. Also, all the languages are linked and provided a common suite to provide a universal communication tool. Because of this structure, built-on functions, and function blocks, users can adopt either a top-down or bottom-up strategy to develop their own programs.

What is CoDeSys?

CoDeSys, short for Controller Development System, is one of the most widely used IEC 61131-3 programming tools for controllers. Developed by Smart Software Solutions GmbH, or 3S, Kempten, Germany, CoDeSys supports all five programming languages of the standard to combine the power of advanced programming languages such as C or Pascal with the handling and operational functions of PLC programming systems.

Unlike other tools, CoDeSys produces native machine code for many common processors. Native machine code is inherently faster and more reliable than interpreted solutions. Other benefits:

Fast customization

Complete test adaptation (including online functionality) can be done on any standard processor hardware within two days, and CoDeSys has ready backends for all current processors. To minimize customization time and resulting expenses, its code generation and run-time and programming systems are coordinated.

Easy to use

Functions such as Autodeclare, Autoformat, and a context-sensitive input assistance simplify the use of CoDeSys. All functions are accessible by keyboard. The tool is efficient because it requires few resources.

High performance

Native code generators for all common processors optimize control-system usage. Intelligent algorithms such as incremental compile assemble large projects with thousands of global variables and hundreds of components quickly. Almost all data types specified in the IEC 61131-3 are accommodated; other features include offline simulation and online breakpoints, single stepping, power flow, sampling traces, and online changes.

For more information on using Freescale processors with embedded open IEC 61131 control software, visit www.rtaautomation.com or call John Rinaldi at (414) 453-5100.

Cutting down on traffic

Using a free, open source, designers can now program Banner SureCross wireless gateways to manipulate data like a PLC.

Real Time Automation recently created the solution for Banner Engineering Corp., Minneapolis, and their wireless product development partner, Sensonix Inc., Plymouth Minn. using CoDeSys 1131-3 open control software. Through a customizable browser-based HMI interface, users can access and manipulate data from multiple wireless sensors.

Placing PLC functionality on the gateway reduces network traffic and can eliminate the need for a PLC in some applications. This reduces the footprint and cost of automating applications. In addition, the browser-based functionality allows users the ability to access data from any internet connection.